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[ot] hw/opentitan: ot_hmac: Restore correct msg_length with HMAC_EN #151

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Mar 20, 2025
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[ot] hw/opentitan: ot_hmac: Restore correct msg_length with HMAC_EN #151

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17 changes: 14 additions & 3 deletions hw/opentitan/ot_hmac.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
* QEMU OpenTitan HMAC device
*
* Copyright (c) 2022-2024 Rivos, Inc.
* Copyright (c) 2024 lowRISC contributors.
* Copyright (c) 2024-2025 lowRISC contributors.
*
* Author(s):
* Loïc Lefort <[email protected]>
Expand Down Expand Up @@ -443,10 +443,21 @@ static void ot_hmac_writeback_digest_state(OtHMACState *s)

static void ot_hmac_restore_context(OtHMACState *s)
{
/*
* When restoring context, if HMAC is enabled we must add the block size to
* the message length to keep our cryptographic library consistent with the
* SW interface. This is because the extra block containing the key XORed
* with the inner pad is not included in the SW-visible message length.
*/
unsigned msg_length = s->regs->msg_length;
if (s->regs->cfg & R_CFG_HMAC_EN_MASK) {
msg_length += ot_hmac_get_block_size_bytes(s) * 8u;
}

switch (s->ctx->digest_size_started) {
case HMAC_SHA2_256:
s->ctx->state.sha256.curlen = 0;
s->ctx->state.sha256.length = s->regs->msg_length;
s->ctx->state.sha256.length = msg_length;
for (unsigned idx = 0; idx < 8u; idx++) {
LOAD32H(s->ctx->state.sha256.state[idx], s->regs->digest + idx);
}
Expand All @@ -458,7 +469,7 @@ static void ot_hmac_restore_context(OtHMACState *s)
*/
case HMAC_SHA2_512:
s->ctx->state.sha512.curlen = 0;
s->ctx->state.sha512.length = s->regs->msg_length;
s->ctx->state.sha512.length = msg_length;
for (unsigned idx = 0; idx < 8u; idx++) {
LOAD64H(s->ctx->state.sha512.state[idx], s->regs->digest + 2 * idx);
}
Expand Down