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fw: Protect zeroisation against compiler optimisation.

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The memset() responsible for the zeroisation of the secure_ctx under
the compute_cdi() function in FW's main.c, was optimised away by the
compiler. Instead of using memset(), secure_wipe() is introduced
which uses a volatile keyword to prevent the compiler to try to
optimise it. Secure_wipe() is now used on all locations handling
removal of sensitive data.
This commit is contained in:
dehanj 2024-02-02 14:20:21 +01:00
parent c85b5311cd
commit 3a6a60ff26
No known key found for this signature in database
GPG Key ID: 3707A9DBF4BB8F1A
3 changed files with 10 additions and 3 deletions
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7
hw/application_fpga/fw/tk1/lib.c
View File

@ -155,3 +155,10 @@ int memeq(void *dest, const void *src, size_t n)
return res; return res;
} }
void secure_wipe(void *v, size_t n)
{
volatile uint8_t *p = (volatile uint8_t *)v;
while (n--)
*p++ = 0;
}

2
hw/application_fpga/fw/tk1/lib.h
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@ -28,5 +28,5 @@ void *memset(void *dest, int c, unsigned n);
void memcpy_s(void *dest, size_t destsize, const void *src, size_t n); void memcpy_s(void *dest, size_t destsize, const void *src, size_t n);
void wordcpy_s(void *dest, size_t destsize, const void *src, size_t n); void wordcpy_s(void *dest, size_t destsize, const void *src, size_t n);
int memeq(void *dest, const void *src, size_t n); int memeq(void *dest, const void *src, size_t n);
void secure_wipe(void *v, size_t n);
#endif #endif

4
hw/application_fpga/fw/tk1/main.c
View File

@ -115,7 +115,7 @@ static void compute_cdi(const uint8_t *digest, const uint8_t use_uss,
// while on the firmware stack which is in the special fw_ram. // while on the firmware stack which is in the special fw_ram.
wordcpy_s(local_uds, 8, (void *)uds, 8); wordcpy_s(local_uds, 8, (void *)uds, 8);
blake2s_update(&secure_ctx, (const void *)local_uds, 32); blake2s_update(&secure_ctx, (const void *)local_uds, 32);
(void)memset(local_uds, 0, 32); (void)secure_wipe(local_uds, sizeof(local_uds));
// Update with TKey program digest // Update with TKey program digest
blake2s_update(&secure_ctx, digest, 32); blake2s_update(&secure_ctx, digest, 32);
@ -130,7 +130,7 @@ static void compute_cdi(const uint8_t *digest, const uint8_t use_uss,
// Clear secure_ctx of any residue of UDS. Don't want to keep // Clear secure_ctx of any residue of UDS. Don't want to keep
// that for long even though fw_ram is cleared later. // that for long even though fw_ram is cleared later.
(void)memset(&secure_ctx, 0, sizeof(secure_ctx)); (void)secure_wipe(&secure_ctx, sizeof(secure_ctx));
// CDI only word writable // CDI only word writable
wordcpy_s((void *)cdi, 8, &local_cdi, 8); wordcpy_s((void *)cdi, 8, &local_cdi, 8);