[crypto] Wipe OTBN's DMEM in failure cases #27650
Open
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Always wipe the DMEM once the OTBN execution has been finished. Signed-off-by: Pascal Nasahl <nasahlpa@lowrisc.org>
nasahlpa
requested review from
alees24,
felixmiller,
vogelpi,
h-filali,
andrea-caforio,
moidx and
cfrantz
and removed request for
a team and
alees24
nasahlpa
added
the
CherryPick:earlgrey_1.0.0
johannheyszl
approved these changes
Jul 21, 2025
moidx
reviewed
Jul 23, 2025
sw/device/lib/crypto/impl/ecc/p256.c
Outdated
| @@ -215,10 +219,12 @@ status_t p256_ecdsa_sign_finalize(p256_ecdsa_signature_t *result) { | |||
| HARDENED_TRY(otbn_busy_wait_for_done()); | |||
There was a problem hiding this comment.
Should calls to otbn_busy_wait_for_done also result in WIPE DMEM?
There was a problem hiding this comment.
Thank you for your feedback!
Yes, this would make sense. I was initially against doing it as OTBN needs to be IDLE when calling otbn_dmem_sec_wipe() and otbn_busy_wait_for_done() can fail with leaving OTBN not IDLE. However otbn_busy_wait_for_done() can also fail with leaving OTBN IDLE (e.g., some error bits are set), then we should wipe it.
I've modified the code that now DMEM gets wiped when otbn_busy_wait_for_done() fails. When otbn_busy_wait_for_done() fails with leaving OTBN not IDLE, the DMEM will not be wiped though.
When an error occurs, HARDENED_TRY() immediately returns. As we also want to wipe the OTBN DMEM when an error happens, this commit adds HARDENED_TRY_WIPE_DMEM() which wipes DMEM on an error before returning. Signed-off-by: Pascal Nasahl <nasahlpa@lowrisc.org>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This commit:
otbn_dmem_sec_wipe()HARDENED_TRY_WIPE_DMEM()macro that wipes the DMEM before returningCloses #20050.