[openssl/openssl] 1a8242: Add constant-time validation for CRYPTO_memcmp

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 1a824261ef16231ea036b7935613ea4b219e3a42
      https://github.com/openssl/openssl/commit/1a824261ef16231ea036b7935613ea4b219e3a42
  Author: David Foster <[email protected]>
  Date:   2026-06-11 (Thu, 11 Jun 2026)

  Changed paths:
    M .github/workflows/ct-validation-daily.yml
    M crypto/cpuid.c
    M test/build.info
    A test/crypto_memcmp_test.c
    A test/recipes/90-test_crypto_memcmp.t

  Log Message:
  -----------
  Add constant-time validation for CRYPTO_memcmp

Add test/crypto_memcmp_test.c which provides functional coverage for
CRYPTO_memcmp under regular builds and constant-time coverage under
enable-ct-validation builds.

The added constant-time coverage checks:
- there are no data dependent branches or memory accesses,
  on x86_64 and aarch64 architectures

The added constant-time coverage does NOT check:
- there are no data-dependent variable-time instructions, such as
  instructions NOT on the x86 Data Operand Independent Timing list
  or NOT on the ARM Data-Independent Timing list
- any architectures beyond x86_64 and aarch64

New CONSTTIME_SECRET annotations live only in the test rather than in
the generic C version of CRYPTO_memcmp so that both the C and
assembler versions of CRYPTO_memcmp are constant-time covered.

CRYPTO_memcmp directly backs CPython's secrets.compare_digest() and
hmac.compare_digest(), so a timing leak in it is high impact, yet it had
essentially no direct test coverage.

References #15076.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Reviewed-by: Milan Broz <[email protected]>
Reviewed-by: Bob Beck <[email protected]>
MergeDate: Thu Jun 11 16:11:58 2026
(Merged from https://github.com/openssl/openssl/pull/31398)



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