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Merge pull request #1367 from gilles-peskine-arm/aesni_has_support-volatile-3.6

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Backport 3.6: Fix race condition in mbedtls_aesni_has_support
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Gilles Peskine
2025-06-13 23:20:28 +02:00
committed by GitHub
parent a79525239f 853cfbdced
commit 3c9ad42719
2 changed files with 30 additions and 2 deletions
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15
library/aesni.c
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@ -48,8 +48,19 @@
*/
int mbedtls_aesni_has_support(unsigned int what)
{
static int done = 0;
static unsigned int c = 0;
/* To avoid a race condition, tell the compiler that the assignment
* `done = 1` and the assignment to `c` may not be reordered.
* https://github.com/Mbed-TLS/mbedtls/issues/9840
*
* Note that we may also be worried about memory access reordering,
* but fortunately the x86 memory model is not too wild: stores
* from the same thread are observed consistently by other threads.
* (See example 8-1 in Sewell et al., "x86-TSO: A Rigorous and Usable
* Programmer’s Model for x86 Multiprocessors", CACM, 2010,
* https://www.cl.cam.ac.uk/~pes20/weakmemory/cacm.pdf)
*/
static volatile int done = 0;
static volatile unsigned int c = 0;
if (!done) {
#if MBEDTLS_AESNI_HAVE_CODE == 2