- TF-A - lists.trustedfirmware.org

by Varun Wadekar

Hello, While reviewing all the compiler flags used by TF-A, we couldn't find information for the following options in the GCC manual [1] * --fatal-warnings (https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/…) * -fno-stack-protector (https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/…) Can someone please help me understand if these options are still valid? Thanks. [1] https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Option-Index.html#Option-Index ----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -----------------------------------------------------------------------------------

5 years, 1 month

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Re: [TF-A] Project Maintenance Proposal for tf.org Projects

by Sandrine Bailleux

Hi all, On 5/5/20 9:04 AM, Sandrine Bailleux via TF-A wrote: > I've received very little feedback on version 2 of the proposal, which > hints that we are reaching an agreement. Thus, I plan to finalize the > proposal this week. This can then become part of our development flow > for all trustedfirmware.org projects. > > Thanks again for all the inputs! The project maintenance process is now live. The document has been moved here (with a few minor edits to turn it from a proposal to an effective process): https://developer.trustedfirmware.org/w/collaboration/project-maintenance-p… Thanks! Regards, Sandrine

5 years, 1 month

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New Defects reported by Coverity Scan for ARM-software/arm-trusted-firmware

by scan-admin＠coverity.com

Hi, Please find the latest report on new defect(s) introduced to ARM-software/arm-trusted-firmware found with Coverity Scan. 1 new defect(s) introduced to ARM-software/arm-trusted-firmware found with Coverity Scan. New defect(s) Reported-by: Coverity Scan Showing 1 of 1 defect(s) ** CID 358027: Insecure data handling (TAINTED_SCALAR) ________________________________________________________________________________________________________ *** CID 358027: Insecure data handling (TAINTED_SCALAR) /common/fdt_wrappers.c: 295 in fdt_get_reg_props_by_name() 289 290 index = fdt_stringlist_search(dtb, node, "reg-names", name); 291 if (index < 0) { 292 return index; 293 } 294 >>> CID 358027: Insecure data handling (TAINTED_SCALAR) >>> Passing tainted variable "index" to a tainted sink. 295 return fdt_get_reg_props_by_index(dtb, node, index, base, size); 296 } 297 298 /******************************************************************************* 299 * This function gets the stdout path node. 300 * It reads the value indicated inside the device tree. ________________________________________________________________________________________________________ To view the defects in Coverity Scan visit, https://u2389337.ct.sendgrid.net/ls/click?upn=nJaKvJSIH-2FPAfmty-2BK5tYpPkl…

5 years, 1 month

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Re: [TF-A] Proposal for Measured Boot Implementation

by Vivek Prasad

Hello Stuart, Alexei, Chiming-in here on Ampere's behalf... We analysed this proposal internally. And we see a number issues with this, some of which was already raised by Raghu in the previous threads. Here is a summary of the main issues that we see. * Only supporting mbedtls, and this is fixed config at compile time. * We propose that there should be a variable for the algorithm to be used, which can be setup at initialization time. * This solution relies on taking the hash directly from the digest as the measurement, instead of the computed hash. This is not safe, especially considering measured boot may use a different hash bank, so digest hash may not be correct/valid. * Only measuring the BL2 image, per the ARM SBSG we must be measuring and logging *all* images/boot phases * BL31 * BL32 (all secure partitions) * BL33 (UEFI or any other non-secure boot loader) * Once we ERET into BL33, the measure boot flow continues and is owned by that boot loader * Only see support for PCR0, any/all unsigned config data must be logged to PCR1. * Passing PCRs to non-secure software before logging is not compliant with TCG Static-Root-of-Trust Measurement (SRTM) requirements * It was discussed before in separate conversations… especially in systems where you are talked about two different signing domains where BL33 is a different trust/signing domain. * BL33 should only do hash-log-extend… there is no need for BL33 to be aware of the current PCR value (beyond what is provided in the boot event log). * Based on comments on the mail thread, there seem to be bad assumptions/expectations around TPM accessibility from non-secure world. * Expecting SPI/I2C TPMs to be directly accessed from non-secure world instead of abstracting hardware details via the TCG CRB interface (which has been already standardized as the defacto mechanism for ARM on past mobile, client, and server solutions). * CRB will "just work" for Aptio/EDK2/Linux/Windows/Hyper-V/VMWare * NOTE: This goes back to what is a “productizable” TPM solution. We want it to be turn-key solution for customers without having to support/develop proprietary drivers. -Vivek/Harb

5 years, 1 month

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TF-A Tech Forum Agenda @ Thr 7th May 2020 17:00-1800 BST

by Joanna Farley

Hi All, The next TF-A Tech Forum is scheduled for Thu 7th May 2020 17:00 - 18:00 (BST). A reoccurring meeting invite has been sent out to the subscribers of this TF-A mailing list. If you don’t have this please let me know. This meeting will be chaired by Bipin Ravi. Agenda: * Overview of a new TF-A Build System based on Cmake by Javier Almansa Sobrino * Optional TF-A Mailing List Topic Discussions Thanks Joanna

5 years, 1 month

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Re: [TF-A] Need input on Errata implementation

by Soby Mathew

> -----Original Message----- > From: TF-A <tf-a-bounces(a)lists.trustedfirmware.org> On Behalf Of Raghu > Krishnamurthy via TF-A > Sent: 30 April 2020 02:33 > To: Manish Badarkhe <Manish.Badarkhe(a)arm.com>; tf- > a(a)lists.trustedfirmware.org > Cc: nd <nd(a)arm.com> > Subject: Re: [TF-A] Need input on Errata implementation > > Hi Manish, > > Really appreciate you for taking time to respond to my concerns/questions. > > What about this situation? NS-EL2 makes an SMC call to EL3 to get some basic > information like GET_SOC_INFORMATION. This is a simple SMC and there is no > call to context save or context restore. During the SMC call, if there is a > speculative AT instruction on a lower EL(say NS-EL2), there could be a bad > cached translation. Do you not need to apply the errata in this situation ? If > not, why? > > >>We can't simply apply this errata on reset and just leave the system. > > [RK]Totally agree. See CPU_E_HANDLER_FUNC. It is not necessary that > cpu_ops are only called during reset and power down. > CPU_E_HANDLER_FUNC is called at runtime due EA's. > > >>We thought of taking different approach for this errata > implementation >>where anybody disable this workaround using macro as > this errata is >>applicable for most of the CPUs (by default enabled) and can't > be >>placed in cpu_ops. > > [RK]This is a poor approach in my view. Most CPU's is not all CPU's. The reason > the errata framework exists is to apply CPU specific erratas by checking for > them dynamically. Different stepping's of the same CPU's may or may not have > the errata and typically you check the MIDR to know if the errata applies or > not. Linux does not apply the errata to all CPU's since "most" CPU's have the > issue. They check for its existence at runtime and only then apply it. TF-A > should not hold itself to a lower standard. Hi Raghu I guess this depends on what the errata workaround involves. Since this workaround applies bit setting on an out of context register, it was not expected to affect the EL3 execution performance (or the lower level EL because the bits are restored on return). Also it was thought that the act of searching through the list of compiled CPUs and checking if the workaround is applicable might be more detrimental than the unilateral application of the workaround for this case (assuming no extra barriers are added since the code path it is inserted in have them already later in the sequence). But I agree it is more elegant to have this coupled into CPU_OPS framework. I think Manish has some ideas for this. Best Regards Soby Mathew > > -Raghu > > On 4/29/20 1:35 AM, Manish Badarkhe wrote: > > Hi Raghu > > > > Just to add/correct one more thing from my previous emails that this errata > workaround proposed is > > applied to both normal and secure world switches to EL3. > > > > Thanks > > Manish Badarkhe > > > > On 29/04/2020, 12:25, "TF-A on behalf of Manish Badarkhe via TF-A" <tf-a- > bounces(a)lists.trustedfirmware.org on behalf of tf-a(a)lists.trustedfirmware.org> > wrote: > > > > Hi Raghu > > > > On 29/04/2020, 02:00, "Raghu K" <raghu.ncstate(a)icloud.com> wrote: > > > > Hi Manish, > > > > Thanks. > > > > >> we don’t have any AT instances in minimum execution window after > context switching from S-EL(1/2) > > >> to EL3 and before updating TCR register. > > > > 1) What is the minimum execution window? Does that not change based > on micro-architecture? > > Not sure about exact minimum execution window. IMO, it really depend > upon when "context_save" gets called after > > entering into EL3 from S-EL1/2. It may changed upon micro-architecture. > Need some experts comment here. > > > > 2) Do we know that the "execution window" is exactly the same for all > the CPU's this errata applies to? > > It may be but we should not worry on that if we don’t have any AT > instruction execution in that window. > > > > Also, it appears we are only talking about switching from S-EL1/2 to EL3. > The same issue can happen when you go from NS-EL1/EL2 to EL3 as well. There > also seems to be an assumption in the patch you submitted that this errata > happens only during a so called context-switch. From my reading, the cortex- > Ax errata notices don't limit the errata to occur only during "context-switches" > in the "conditions" section and can occur while executing ANY code, although > the work around section does muddy the waters a bit. > > > > In Linux, at NS-EL2 this workaround is already in place. Hence we just > thought of considering cases from Secure EL side to put this workaround. > > Yes, errata should not limit to particular conditional section but this > particular errata is not straight-forward like another errata placed in the code > currently. We can't simply apply this errata on reset and just leave the system. > > > > Back to problem, AT instruction speculative execution using out-of- > context regime that results in page table walk and generate the incorrect > > translation which are cached in TLB. To avoid this issue we thought of > disabling PTW for that particular EL. > > for e.g. If AT instruction execution for EL1 present in EL3 then we have to > make sure speculative behaviour of this AT should not result in incorrect > translation cached in TLB. If system is always in EL3 (if we loop-in in EL3 always > without going back and forth to/from lower EL) then in that case > > there is no need of this workaround. > > Hence we thought to put this workaround over boundary context of > context switches. When "context save" (close to EL3 entry) happened we > meticulously save all EL system registers (S-EL1/S-EL2) with PTW disabled and > continue EL3 execution with PTW disabled ensuring we should not cache any > incorrect translation for (S-EL1/S-EL2) and during "context restore" (i.e. close > to EL3 exit) again we disabled PTW, restore all system registers for EL (S-EL1/S- > EL2) except TCR and then restore TCR. > > > > 3) Has there been any work done to actually reproduce this issue and > also to see that this actually fixes the issue? > > No this issue is hard to reproduce. > > > > 4) Has the CPU errata framework(cpu_ops etc.) been considered to > possibly implement the errata? Sprinkling erratas through common framework > code does not seem like a good idea. > > We thought of taking different approach for this errata implementation > where anybody disable this workaround using macro as this errata is > applicable for most of the CPUs (by default enabled) and can't be placed in > cpu_ops. > > > > Thanks > > Raghu > > > > Thanks > > Manish Badarkhe > > > > On 4/28/20 1:44 AM, Manish Badarkhe wrote: > > > Hi Raghu > > > > > > Please see my replies inline. > > > > > > Regards > > > Manish Badarkhe > > > > > > On 28/04/2020, 11:29, "Raghu Krishnamurthy" > <raghu.ncstate(a)icloud.com> wrote: > > > > > > Hi Manish, > > > > > > Understood. > > > > > > >>Hence before entering in EL3, we ensured that PTW is disabled > (at > > > context save) > > > > > > The context save and restore functions are executed in EL3. So how > are > > > you disabling PTW before entering EL3 ? > > > > > > Yes, I put it wrongly. We thought "context_save/restore" is best place > to disable PTW without much affecting the > > > code because we don’t have any AT instances in minimum execution > window after context switching from S-EL(1/2) > > > to EL3 and before updating TCR register. > > > > > > -Raghu > > > > > > Thanks > > > Manish Badarkhe > > > > > > On 4/27/20 10:53 PM, Manish Badarkhe wrote: > > > > Hi Raghu > > > > > > > > This workaround is specifically need for speculative AT instruction > behaviour in out of context regime. > > > > That means executing AT instruction for lower ELs (S-EL1/S-EL2) in > higher EL i.e. EL3. > > > > > > > > Behaviour of AT instruction is unaltered when it get executed in > same regime (when AT instruction executed for same EL > > > > where it is executing) and there is no possibility to execute AT > instruction for higher EL in lower EL. > > > > > > > > Hence before entering in EL3, we ensured that PTW is disabled (at > context save) and restore PTW back during > > > > exit of EL3. (at context restore). > > > > > > > > Thanks > > > > Manish Badarkhe > > > > > > > > On 28/04/2020, 01:23, "Raghu K" <raghu.ncstate(a)icloud.com> > wrote: > > > > > > > > Hi Manish, > > > > > > > > >>Hence proposed solution will work as it is > > > > > > > > [RK]If you are sure go ahead. I'm not convinced, but that may > be because > > > > i don't understand the errata fully/correctly. > > > > > > > > >>This workaround is very specific during context switching > > > > > > > > [RK] Context switching has many meanings depending on the > context(OS, > > > > hypervisor, TF-A world switch etc). The errata document i saw > does not > > > > elaborate on this. Perhaps clarifying this will help understand > why the > > > > solution you proposed will work. > > > > > > > > The solution below in points 2 and 3 have the same problem on > entry and > > > > exit, mentioned in my first email. Before you call > > > > el1_sysregs_context_save, an AT instruction could have > speculatively > > > > executed through speculation of branches that occur BEFORE > you call this > > > > function, when TCR still has the enable bit set. The fact that you > don't > > > > have an AT instruction in the context save routine or any > routine for > > > > that matter, does not guarantee that the hardware did not > speculate > > > > through some other means to reach an AT instruction. The > same applies to > > > > the context_restore routines. There is no guarantee right after > you > > > > finish the restore routing(and hence TCR has the enable bit set), > that > > > > the CPU cannot speculate to an AT instruction. > > > > So i'm not clear how you can say for certain that there was no > > > > speculative AT instruction with the proposal below. > > > > > > > > Thanks > > > > Raghu > > > > > > > > On 4/27/20 10:08 AM, Manish Badarkhe wrote: > > > > > Hi All, > > > > > > > > > > Just update/correct details. > > > > > > > > > > Thanks > > > > > Manish Badarkhe > > > > > > > > > > On 27/04/2020, 22:13, "TF-A on behalf of Manish Badarkhe > via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf- > a(a)lists.trustedfirmware.org> wrote: > > > > > > > > > > Hi Raghu > > > > > > > > > > Please ignore my answer on question 2. > > > > > > > > > > With internal discussion came to below conclusion: > > > > > 1. This workaround is very specific during context > switching. > > > > > 2 . If you check in context save routine > (el1_sysregs_context_save or el2_sysregs_context_save), > > > > > As per proposed solution, First step performed is to > disable page table walk and we don’t have > > > > > any AT instruction execution in context save routine. > > > > > This ensures that there will be no possibility of > speculative AT instruction execution without TCR update. > > > > > 3. If you check in context restore routine > (el1_sysregs_context_restore or el2_sysregs_context_restore), > > > > > As per proposed solution, first step performed is to > disable page table walk and we don’t have any > > > > > AT instruction execution in context restore routine. > > > > > This ensures that there will be no possibility of > speculative AT instruction execution without TCR update. > > > > > > > > > > Hence proposed solution will work as it is ensuring no > caching of translations in TLB while speculative AT instruction execution. > > > > > > > > > > Thanks > > > > > Manish Badarkhe > > > > > > > > > > On 27/04/2020, 13:38, "TF-A on behalf of Manish Badarkhe > via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf- > a(a)lists.trustedfirmware.org> wrote: > > > > > > > > > > Hi Raghu > > > > > > > > > > Please see my answers inline > > > > > > > > > > On 25/04/2020, 06:38, "TF-A on behalf of Raghu K via TF- > A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf- > a(a)lists.trustedfirmware.org> wrote: > > > > > > > > > > Hi Manish, > > > > > > > > > > Before I agree or disagree with the suggested fix, the > following would > > > > > be interesting to know/discuss. Please feel free to > correct me if i've > > > > > misunderstood something. > > > > > > > > > > 1) Are "speculative" AT instructions subject to TCR_ELx > control bits for > > > > > all the listed CPU's? I imagine the answer is yes but > would be good to > > > > > get confirmation. I could not find any evidence in the > instruction > > > > > description or psuedocode in the ARMv8 ARM. It is > possible to play many > > > > > tricks on speculative execution of instructions such as > skipping checks > > > > > and doing them only when the CPU knows the > instruction will be > > > > > committed. If this is the case, changing TCR_ELx bits > may not work. The > > > > > errata document is vague about how to fix it. > > > > > > > > > > The speculative AT instruction may behave as you > mentioned. We need more > > > > > opinion on this. > > > > > Proposed fix I mentioned by referring linux workaround > for the same errata. > > > > > Linux workaround is available in mainline kernel as > below: > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?… > v5.7-rc3&id=bd227553ad5077f21ddb382dcd910ba46181805a > > > > > > > > > > 2) Assuming the answer to question 1 is yes, your > proposal may not work > > > > > as is. In the worst case, as soon as you enter EL3, the > very first thing > > > > > that may happen, before you ever operate/write to > TCR_ELx, is a > > > > > speculative AT instruction that caches a bad translation > in the TLB's. > > > > > The same thing can happen on the exit path. As soon as > you restore the > > > > > TCR_ELx register, the first thing that can happen is a > speculative AT > > > > > that caches a bad translation. However, the el3_exit > path does have DSB > > > > > before ERET, so we will not speculate to an AT > instruction if there are > > > > > no branches between the instruction that sets TCR_ELx > and the ERET. > > > > > Somewhere in between, it looks like we will need a > TLBI NSH to be > > > > > certain there are no bad translation cached. This > obviously has a > > > > > potential performance cost on the lower EL's. Every > entry into EL3 > > > > > flushes the TLB for lower EL's. > > > > > > > > > > Yes, this seems to be valid case during entry and exit path. > > > > > I am not quite sure in that case where we need to avoid > PTW. > > > > > Also "TLBI NSH" works but it may cause performance > issue. > > > > > Need some more opinion/thoughts on this. > > > > > > > > > > Just thinking, can sequence mentioned for context save > does not ensure that > > > > > PTW is disabled? > > > > > Something as below as last step in ELx(1/2) context save > (elaborated more): > > > > > > ·Save TCR register with PTW enable (EPD=0). (Just to > enable PTW during > > > > > > restore context). Do not operate TCR_EL1x register > here just save its value to restore. > > > > > > This ensures that during entry in EL3 there will be no > chance of PTW > > > > > >. while executing AT instruction. > > > > > > > > > > Thanks > > > > > > > > > > Raghu > > > > > > > > > > Thanks > > > > > Manish Badarkhe > > > > > > > > > > On 4/24/20 2:56 AM, Manish Badarkhe via TF-A wrote: > > > > > > > > > > > > Hi All > > > > > > > > > > > > We are trying to implement errata which is applicable > for below CPUs: > > > > > > > > > > > > <CPUs> : <Errata No.> > > > > > > > > > > > > Cortex-A53: 1530924 > > > > > > > > > > > > Cortex-A76: 1165522 > > > > > > Cortex-A72: 1319367 > > > > > > Cortex-A57: 1319537 > > > > > > Cortex-A55: 1530923 > > > > > > > > > > > > *Errata Description:* > > > > > > > > > > > > A speculative Address Translation (AT) instruction > translates using > > > > > > registers that are associated with an out-of-context > translation > > > > > > regime and caches the resulting translation in the TLB. > A subsequent > > > > > > translation request that is generated when the out- > of-context > > > > > > translation regime is current uses the previous cached > TLB entry > > > > > > producing an incorrect virtual to physical mapping. > > > > > > > > > > > > *Probable solution is to implement below fix in > context.S file:* > > > > > > > > > > > > *During ELx (1 or 2) context save:* > > > > > > > > > > > > ·Operate TCR_ELx(1/2) to disable page table walk by > operating EPD bits > > > > > > > > > > > > oThis will avoid any page table walk for S-EL1 or S-EL2. > This will > > > > > > help in avoiding caching of translations in TLB > > > > > > > > > > > > for S-EL1/S-EL2 in EL3. > > > > > > > > > > > > ·Save all system registers (which is already available) > except TCR > > > > > > > > > > > > ·Clear EPD bits of TCR and then save. (Just to enable > PTW during > > > > > > restore context). > > > > > > > > > > > > *During ELx (1 or 2) context restore:* > > > > > > > > > > > > * Operate TCR_ELx(1/2) to disable page table walk > by operating EPD bits > > > > > > * Restore all system registers (which are saved > during context save) > > > > > > except TCR register. > > > > > > * Restore TCR_ELx(1/2) register (which enable back > PTW). > > > > > > > > > > > > With above we ensured that there will be no page > table walk for S-EL1 > > > > > > and S-EL2 in EL3. > > > > > > > > > > > > is this proper other way to fix this problem? Need > some suggestion/use > > > > > > cases where and all we need this workaround in TF-A > code. > > > > > > > > > > > > Thanks > > > > > > > > > > > > Manish Badarkhe > > > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and > any attachments are > > > > > > confidential and may also be privileged. If you are not > the intended > > > > > > recipient, please notify the sender immediately and > do not disclose > > > > > > the contents to any other person, use it for any > purpose, or store or > > > > > > copy the information in any medium. Thank you. > > > > > > > > > > > > > > > > -- > > > > > TF-A mailing list > > > > > TF-A(a)lists.trustedfirmware.org > > > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and any > attachments are confidential and may also be privileged. If you are not the > intended recipient, please notify the sender immediately and do not disclose > the contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > > > > -- > > > > > TF-A mailing list > > > > > TF-A(a)lists.trustedfirmware.org > > > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and any > attachments are confidential and may also be privileged. If you are not the > intended recipient, please notify the sender immediately and do not disclose > the contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > > > > -- > > > > > TF-A mailing list > > > > > TF-A(a)lists.trustedfirmware.org > > > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and any > attachments are confidential and may also be privileged. If you are not the > intended recipient, please notify the sender immediately and do not disclose > the contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and any > attachments are confidential and may also be privileged. If you are not the > intended recipient, please notify the sender immediately and do not disclose > the contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > > > > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments > are confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > > > > > -- > > TF-A mailing list > > TF-A(a)lists.trustedfirmware.org > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > -- > TF-A mailing list > TF-A(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/tf-a

5 years, 1 month

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Re: [TF-A] Project Maintenance Proposal for tf.org Projects

by Sandrine Bailleux

Hi all, I've received very little feedback on version 2 of the proposal, which hints that we are reaching an agreement. Thus, I plan to finalize the proposal this week. This can then become part of our development flow for all trustedfirmware.org projects. Thanks again for all the inputs! Regards, Sandrine Bailleux

5 years, 1 month

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Re: [TF-A] [RFC] isolation between runtime BL33 services and OS

by Achin Gupta

Hi Francois, On Mon, Apr 20, 2020 at 11:45:02AM +0000, François Ozog via TF-A wrote: > Hi, > > I am trying to identify a mechanism to enforce a form of two-way > isolation between BL33 runtime services in OS, for instance: > - a pair of 2MB areas that could be RO by one entity and RW by the other > - an execute only BL33 2MB area? Stupid Q! Are you referring to isolation between EFI runtime services and the OS? It is not clear what you mean by BL33 runtime services? cheers, Achin > > This is similar to hypervisor except it only deals with memory, no > vCPU, no GIC virtualization... > > Could EL3 or EL2 install protective mappings ? BL33 could ask either > EL2 hypervisor or SecureMonitor to actually install them. > > Cordially, > > FF > -- > TF-A mailing list > TF-A(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/tf-a IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 1 month

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Re: [TF-A] Need input on Errata implementation

by Manish Badarkhe

Hi Raghu Just to add/correct one more thing from my previous emails that this errata workaround proposed is applied to both normal and secure world switches to EL3. Thanks Manish Badarkhe On 29/04/2020, 12:25, "TF-A on behalf of Manish Badarkhe via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf-a(a)lists.trustedfirmware.org> wrote: Hi Raghu On 29/04/2020, 02:00, "Raghu K" <raghu.ncstate(a)icloud.com> wrote: Hi Manish, Thanks. >> we don’t have any AT instances in minimum execution window after context switching from S-EL(1/2) >> to EL3 and before updating TCR register. 1) What is the minimum execution window? Does that not change based on micro-architecture? Not sure about exact minimum execution window. IMO, it really depend upon when "context_save" gets called after entering into EL3 from S-EL1/2. It may changed upon micro-architecture. Need some experts comment here. 2) Do we know that the "execution window" is exactly the same for all the CPU's this errata applies to? It may be but we should not worry on that if we don’t have any AT instruction execution in that window. Also, it appears we are only talking about switching from S-EL1/2 to EL3. The same issue can happen when you go from NS-EL1/EL2 to EL3 as well. There also seems to be an assumption in the patch you submitted that this errata happens only during a so called context-switch. From my reading, the cortex-Ax errata notices don't limit the errata to occur only during "context-switches" in the "conditions" section and can occur while executing ANY code, although the work around section does muddy the waters a bit. In Linux, at NS-EL2 this workaround is already in place. Hence we just thought of considering cases from Secure EL side to put this workaround. Yes, errata should not limit to particular conditional section but this particular errata is not straight-forward like another errata placed in the code currently. We can't simply apply this errata on reset and just leave the system. Back to problem, AT instruction speculative execution using out-of-context regime that results in page table walk and generate the incorrect translation which are cached in TLB. To avoid this issue we thought of disabling PTW for that particular EL. for e.g. If AT instruction execution for EL1 present in EL3 then we have to make sure speculative behaviour of this AT should not result in incorrect translation cached in TLB. If system is always in EL3 (if we loop-in in EL3 always without going back and forth to/from lower EL) then in that case there is no need of this workaround. Hence we thought to put this workaround over boundary context of context switches. When "context save" (close to EL3 entry) happened we meticulously save all EL system registers (S-EL1/S-EL2) with PTW disabled and continue EL3 execution with PTW disabled ensuring we should not cache any incorrect translation for (S-EL1/S-EL2) and during "context restore" (i.e. close to EL3 exit) again we disabled PTW, restore all system registers for EL (S-EL1/S-EL2) except TCR and then restore TCR. 3) Has there been any work done to actually reproduce this issue and also to see that this actually fixes the issue? No this issue is hard to reproduce. 4) Has the CPU errata framework(cpu_ops etc.) been considered to possibly implement the errata? Sprinkling erratas through common framework code does not seem like a good idea. We thought of taking different approach for this errata implementation where anybody disable this workaround using macro as this errata is applicable for most of the CPUs (by default enabled) and can't be placed in cpu_ops. Thanks Raghu Thanks Manish Badarkhe On 4/28/20 1:44 AM, Manish Badarkhe wrote: > Hi Raghu > > Please see my replies inline. > > Regards > Manish Badarkhe > > On 28/04/2020, 11:29, "Raghu Krishnamurthy" <raghu.ncstate(a)icloud.com> wrote: > > Hi Manish, > > Understood. > > >>Hence before entering in EL3, we ensured that PTW is disabled (at > context save) > > The context save and restore functions are executed in EL3. So how are > you disabling PTW before entering EL3 ? > > Yes, I put it wrongly. We thought "context_save/restore" is best place to disable PTW without much affecting the > code because we don’t have any AT instances in minimum execution window after context switching from S-EL(1/2) > to EL3 and before updating TCR register. > > -Raghu > > Thanks > Manish Badarkhe > > On 4/27/20 10:53 PM, Manish Badarkhe wrote: > > Hi Raghu > > > > This workaround is specifically need for speculative AT instruction behaviour in out of context regime. > > That means executing AT instruction for lower ELs (S-EL1/S-EL2) in higher EL i.e. EL3. > > > > Behaviour of AT instruction is unaltered when it get executed in same regime (when AT instruction executed for same EL > > where it is executing) and there is no possibility to execute AT instruction for higher EL in lower EL. > > > > Hence before entering in EL3, we ensured that PTW is disabled (at context save) and restore PTW back during > > exit of EL3. (at context restore). > > > > Thanks > > Manish Badarkhe > > > > On 28/04/2020, 01:23, "Raghu K" <raghu.ncstate(a)icloud.com> wrote: > > > > Hi Manish, > > > > >>Hence proposed solution will work as it is > > > > [RK]If you are sure go ahead. I'm not convinced, but that may be because > > i don't understand the errata fully/correctly. > > > > >>This workaround is very specific during context switching > > > > [RK] Context switching has many meanings depending on the context(OS, > > hypervisor, TF-A world switch etc). The errata document i saw does not > > elaborate on this. Perhaps clarifying this will help understand why the > > solution you proposed will work. > > > > The solution below in points 2 and 3 have the same problem on entry and > > exit, mentioned in my first email. Before you call > > el1_sysregs_context_save, an AT instruction could have speculatively > > executed through speculation of branches that occur BEFORE you call this > > function, when TCR still has the enable bit set. The fact that you don't > > have an AT instruction in the context save routine or any routine for > > that matter, does not guarantee that the hardware did not speculate > > through some other means to reach an AT instruction. The same applies to > > the context_restore routines. There is no guarantee right after you > > finish the restore routing(and hence TCR has the enable bit set), that > > the CPU cannot speculate to an AT instruction. > > So i'm not clear how you can say for certain that there was no > > speculative AT instruction with the proposal below. > > > > Thanks > > Raghu > > > > On 4/27/20 10:08 AM, Manish Badarkhe wrote: > > > Hi All, > > > > > > Just update/correct details. > > > > > > Thanks > > > Manish Badarkhe > > > > > > On 27/04/2020, 22:13, "TF-A on behalf of Manish Badarkhe via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf-a(a)lists.trustedfirmware.org> wrote: > > > > > > Hi Raghu > > > > > > Please ignore my answer on question 2. > > > > > > With internal discussion came to below conclusion: > > > 1. This workaround is very specific during context switching. > > > 2 . If you check in context save routine (el1_sysregs_context_save or el2_sysregs_context_save), > > > As per proposed solution, First step performed is to disable page table walk and we don’t have > > > any AT instruction execution in context save routine. > > > This ensures that there will be no possibility of speculative AT instruction execution without TCR update. > > > 3. If you check in context restore routine (el1_sysregs_context_restore or el2_sysregs_context_restore), > > > As per proposed solution, first step performed is to disable page table walk and we don’t have any > > > AT instruction execution in context restore routine. > > > This ensures that there will be no possibility of speculative AT instruction execution without TCR update. > > > > > > Hence proposed solution will work as it is ensuring no caching of translations in TLB while speculative AT instruction execution. > > > > > > Thanks > > > Manish Badarkhe > > > > > > On 27/04/2020, 13:38, "TF-A on behalf of Manish Badarkhe via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf-a(a)lists.trustedfirmware.org> wrote: > > > > > > Hi Raghu > > > > > > Please see my answers inline > > > > > > On 25/04/2020, 06:38, "TF-A on behalf of Raghu K via TF-A" <tf-a-bounces(a)lists.trustedfirmware.org on behalf of tf-a(a)lists.trustedfirmware.org> wrote: > > > > > > Hi Manish, > > > > > > Before I agree or disagree with the suggested fix, the following would > > > be interesting to know/discuss. Please feel free to correct me if i've > > > misunderstood something. > > > > > > 1) Are "speculative" AT instructions subject to TCR_ELx control bits for > > > all the listed CPU's? I imagine the answer is yes but would be good to > > > get confirmation. I could not find any evidence in the instruction > > > description or psuedocode in the ARMv8 ARM. It is possible to play many > > > tricks on speculative execution of instructions such as skipping checks > > > and doing them only when the CPU knows the instruction will be > > > committed. If this is the case, changing TCR_ELx bits may not work. The > > > errata document is vague about how to fix it. > > > > > > The speculative AT instruction may behave as you mentioned. We need more > > > opinion on this. > > > Proposed fix I mentioned by referring linux workaround for the same errata. > > > Linux workaround is available in mainline kernel as below: > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?… > > > > > > 2) Assuming the answer to question 1 is yes, your proposal may not work > > > as is. In the worst case, as soon as you enter EL3, the very first thing > > > that may happen, before you ever operate/write to TCR_ELx, is a > > > speculative AT instruction that caches a bad translation in the TLB's. > > > The same thing can happen on the exit path. As soon as you restore the > > > TCR_ELx register, the first thing that can happen is a speculative AT > > > that caches a bad translation. However, the el3_exit path does have DSB > > > before ERET, so we will not speculate to an AT instruction if there are > > > no branches between the instruction that sets TCR_ELx and the ERET. > > > Somewhere in between, it looks like we will need a TLBI NSH to be > > > certain there are no bad translation cached. This obviously has a > > > potential performance cost on the lower EL's. Every entry into EL3 > > > flushes the TLB for lower EL's. > > > > > > Yes, this seems to be valid case during entry and exit path. > > > I am not quite sure in that case where we need to avoid PTW. > > > Also "TLBI NSH" works but it may cause performance issue. > > > Need some more opinion/thoughts on this. > > > > > > Just thinking, can sequence mentioned for context save does not ensure that > > > PTW is disabled? > > > Something as below as last step in ELx(1/2) context save (elaborated more): > > > > ·Save TCR register with PTW enable (EPD=0). (Just to enable PTW during > > > > restore context). Do not operate TCR_EL1x register here just save its value to restore. > > > > This ensures that during entry in EL3 there will be no chance of PTW > > > >. while executing AT instruction. > > > > > > Thanks > > > > > > Raghu > > > > > > Thanks > > > Manish Badarkhe > > > > > > On 4/24/20 2:56 AM, Manish Badarkhe via TF-A wrote: > > > > > > > > Hi All > > > > > > > > We are trying to implement errata which is applicable for below CPUs: > > > > > > > > <CPUs> : <Errata No.> > > > > > > > > Cortex-A53: 1530924 > > > > > > > > Cortex-A76: 1165522 > > > > Cortex-A72: 1319367 > > > > Cortex-A57: 1319537 > > > > Cortex-A55: 1530923 > > > > > > > > *Errata Description:* > > > > > > > > A speculative Address Translation (AT) instruction translates using > > > > registers that are associated with an out-of-context translation > > > > regime and caches the resulting translation in the TLB. A subsequent > > > > translation request that is generated when the out-of-context > > > > translation regime is current uses the previous cached TLB entry > > > > producing an incorrect virtual to physical mapping. > > > > > > > > *Probable solution is to implement below fix in context.S file:* > > > > > > > > *During ELx (1 or 2) context save:* > > > > > > > > ·Operate TCR_ELx(1/2) to disable page table walk by operating EPD bits > > > > > > > > oThis will avoid any page table walk for S-EL1 or S-EL2. This will > > > > help in avoiding caching of translations in TLB > > > > > > > > for S-EL1/S-EL2 in EL3. > > > > > > > > ·Save all system registers (which is already available) except TCR > > > > > > > > ·Clear EPD bits of TCR and then save. (Just to enable PTW during > > > > restore context). > > > > > > > > *During ELx (1 or 2) context restore:* > > > > > > > > * Operate TCR_ELx(1/2) to disable page table walk by operating EPD bits > > > > * Restore all system registers (which are saved during context save) > > > > except TCR register. > > > > * Restore TCR_ELx(1/2) register (which enable back PTW). > > > > > > > > With above we ensured that there will be no page table walk for S-EL1 > > > > and S-EL2 in EL3. > > > > > > > > is this proper other way to fix this problem? Need some suggestion/use > > > > cases where and all we need this workaround in TF-A code. > > > > > > > > Thanks > > > > > > > > Manish Badarkhe > > > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments are > > > > confidential and may also be privileged. If you are not the intended > > > > recipient, please notify the sender immediately and do not disclose > > > > the contents to any other person, use it for any purpose, or store or > > > > copy the information in any medium. Thank you. > > > > > > > > > > -- > > > TF-A mailing list > > > TF-A(a)lists.trustedfirmware.org > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. > > > -- > > > TF-A mailing list > > > TF-A(a)lists.trustedfirmware.org > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. > > > -- > > > TF-A mailing list > > > TF-A(a)lists.trustedfirmware.org > > > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. > > > > > > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. > > > > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. -- TF-A mailing list TF-A(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/tf-a

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