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fw: Use byte readable UDS

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UDS is now byte readable (but not writable).

Use UDS and USS directly in a blake2s_update() instead of
concatenating them into fw_ram. UDS will still live for a short while
in fw_ram in the blake2s context buffer but will soon be overwritten.

Signed-off-by: Daniel Lublin <daniel@lublin.se>
This commit is contained in:
Michael Cardell Widerkrantz 2023-03-01 15:10:27 +01:00 committed by Daniel Lublin
parent b34fdbcd37
commit 65f100a3c0
No known key found for this signature in database
GPG Key ID: 75BD0FEB8D3E7830
1 changed files with 21 additions and 20 deletions
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41
hw/application_fpga/fw/tk1/main.c
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@ -95,13 +95,8 @@ static void print_digest(uint8_t *md)
static void compute_cdi(uint8_t digest[32], uint8_t use_uss, uint8_t uss[32])
{
uint32_t local_cdi[8];
int len;
// To protect UDS we use a special firmware-only RAM for both
// the in parameter to blake2s and the blake2s context.
// Prepare to sleep a random number of cycles before reading out UDS to
// FW RAM
// Prepare to sleep a random number of cycles before reading out UDS
*timer_prescaler = 1;
while ((*trng_status & (1 << TK1_MMIO_TRNG_STATUS_READY_BIT)) == 0) {
}
@ -113,27 +108,33 @@ static void compute_cdi(uint8_t digest[32], uint8_t use_uss, uint8_t uss[32])
while (*timer_status & (1 << TK1_MMIO_TIMER_STATUS_RUNNING_BIT)) {
}
// Only word aligned access to UDS
wordcpy_s((void *)fw_ram, TK1_MMIO_FW_RAM_SIZE, (void *)uds, 8);
memcpy_s((void *)&fw_ram[32], TK1_MMIO_FW_RAM_SIZE - 32, digest, 32);
// Use firmware-only RAM for BLAKE2s context instead of
// ordinary RAM
blake2s_ctx *secure_ctx = (blake2s_ctx *)fw_ram;
int blake2err = blake2s_init(secure_ctx, 32, NULL, 0);
assert(blake2err == 0);
// Update hash with UDS. This means UDS will live for a short
// while in secure_ctx->b which is in the special fw_ram.
blake2s_update(secure_ctx, (const void *)uds, 32);
// Update with TKey program digest
blake2s_update(secure_ctx, digest, 32);
// Possibly hash in the USS as well
if (use_uss != 0) {
memcpy_s((void *)&fw_ram[64], TK1_MMIO_FW_RAM_SIZE - 64, uss,
32);
len = 96;
} else {
len = 64;
blake2s_update(secure_ctx, uss, 32);
}
blake2s_ctx *secure_ctx = (blake2s_ctx *)(fw_ram + len);
blake2s((void *)local_cdi, 32, NULL, 0, (const void *)fw_ram, len,
secure_ctx);
// Write hashed result to Compound Device Identity (CDI)
blake2s_final(secure_ctx, local_cdi);
// Write over the firmware-only RAM
memset((void *)fw_ram, 0, TK1_MMIO_FW_RAM_SIZE);
// Only word aligned access to CDI
wordcpy_s((void *)cdi, 8, (void *)local_cdi, 8);
// CDI only word writable
wordcpy_s((void *)cdi, 8, local_cdi, 8);
}
enum state {