Hello
Gilles,
Thank
you for your reply. I can try submitting a patch, but I have
never worked with Github so far, so I first need to figure
out how that works
đ
After
digging a bit deeper, I have some concerns about the types
that can reasonably be used for
MBEDTLS_PLATFORM_TIME_TYPE_MACRO. Iâm hesitant to submit a
patch unless I understand its effects.
From
x509.c:
int
mbedtls_x509_time_gmtime(mbedtls_time_t tt,
mbedtls_x509_time *now)
{
struct tm tm;
if (mbedtls_platform_gmtime_r(&tt, &tm) == NULL) {
return -1;
}
now->year = tm.tm_year + 1900;
now->mon = tm.tm_mon + 1;
now->day = tm.tm_mday;
now->hour = tm.tm_hour;
now->min = tm.tm_min;
now->sec = tm.tm_sec;
return 0;
}
static
int x509_get_current_time(mbedtls_x509_time *now)
{
return mbedtls_x509_time_gmtime(mbedtls_time(NULL), now);
}
x509_get_current_time()
passes the output of the custom mbedtls_time() directly to
mbedtls_x509_time_gmtime(), where it is immediately passed
to mbedtls_platform_gmtime_r().
For
this particular piece of code,
MBEDTLS_PLATFORM_TIME_TYPE_MACRO could be anything (basic
type, structure, function pointer, etc.), as long as the
custom mbedtls_platform_gmtime_r() can process the return
value from the custom mbedtls_time().
However,
if the return value of mbedtls_time() is used somewhere in
Mbed TLS without
passing it through mbedtls_platform_gmtime_r(), then the
caller likely expects that mbedtls_time() behaves like the
time() function of <time.h>.
MBEDTLS_PLATFORM_TIME_TYPE_MACRO must then have the same
properties as time_t (as defined in the C standard), or at
least it must have those properties that
Mbed TLS relies
on.
To
add a compile-time check for suitable configurations of
MBEDTLS_PLATFORM_TIME_TYPE_MACRO, I would need to know what
properties
Mbed TLS expects
from it, and then somehow check if the custom
MBEDTLS_PLATFORM_TIME_TYPE_MACRO type has these properties.
We
only use a subset of
Mbed TLS in
our application. Using uint32_t for
MBEDTLS_PLATFORM_TIME_TYPE_MACRO might work for us, but
maybe there are other features in
Mbed TLS where
it would fail. I havenât searched through the whole
Mbed TLS code.
Is
it certain that the only thing that is ever done with the
return value of mbedtls_time(), is that it is being passed
to mbedtls_platform_gmtime_r()? I.e. the only purpose of
MBEDTLS_PLATFORM_TIME_TYPE_MACRO is to align the return type
of mbedtls_time() with the type of the first parameter of
mbedtls_platform_gmtime_r()?
Best
regards,
Ralf
KION Supply Chain Solutions
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Hello,
I agree that this looks like a mistake. The various platform
interfaces are subtly different, and I suspect that this was
inspired by a similar check for a different interface that
doesn't apply here. This is not tested (I think we have no
tests for custom platform types).
Can you please submit a patch?
--
Best regards,
Gilles Peskine
TF-PSA-Crypto and Mbed TLS developer
On 18/07/2026 15:15,
Huber, Ralf via mbed-tls wrote:
Dear
Mbed TLS contributors,
We
are using mbedtls v4 for X.509 certificate verification on
a 32 bit microcontroller. The device has an RTC chip and
we use its time for mbedtls by defining
MBEDTLS_PLATFORM_TIME_ALT. This is working so far.
The
compiler provides <time.h>, with time_t being a
signed 32 bit type. I would like to stop mbedtls from
using the date and time functions of <time.h> and
change mbedtls_time_t to unsigned 32 bit to avoid
the year 2038 problem (when signed 32 bit time_t will
overflow). To do this, I defined
#define
MBEDTLS_PLATFORM_TIME_TYPE_MACRO unsigned long
I
also changed the custom time function
(MBEDTLS_PLATFORM_TIME_ALT) to return unsigned values and
I defined MBEDTLS_PLATFORM_GMTIME_R_ALT and provided a
custom mbedtls_platform_gmtime_r() that accepts unsigned
values.
When
I build mbedtls with these settings, I get an error from
tf_psa_crypto_check_config.h:
#if
defined(MBEDTLS_PLATFORM_TIME_TYPE_MACRO) &&\
( defined(MBEDTLS_PLATFORM_STD_TIME) ||\
defined(MBEDTLS_PLATFORM_TIME_ALT) )
#error
"MBEDTLS_PLATFORM_TIME_TYPE_MACRO and
MBEDTLS_PLATFORM_STD_TIME/MBEDTLS_PLATFORM_TIME_ALT cannot
be defined simultaneously"
#endif
I
wonder if this check is actually necessary or maybe a
mistake? Actually, I expected the opposite, i.e.
#if
defined(MBEDTLS_PLATFORM_TIME_TYPE_MACRO) &&\
!( defined(MBEDTLS_PLATFORM_STD_TIME) ||\
defined(MBEDTLS_PLATFORM_TIME_ALT) )
#error
"Must provide alternate time() function compatible with
type defined by MBEDTLS_PLATFORM_TIME_TYPE_MACRO"
#endif
Could
somebody please explain why
MBEDTLS_PLATFORM_TIME_TYPE_MACRO canât be used with
MBEDTLS_PLATFORM_TIME_ALT? Can/Should I comment out the
#error? I tried that and the library compiles without
errors, and the software using the library also compiles
without errors, but I have not yet checked, if it actually
works.
Best
regards,
Ralf
Huber
KION
Supply Chain Solutions
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