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Use alignment-safe writes in ML-KEM mlkem_vec_compress_10_c

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The little-endian large-code path of mlkem_vec_compress_10_c cast the
output byte buffer to word32* and issued five 32-bit stores through it.
That buffer is the caller-supplied ML-KEM ciphertext, which has no
alignment guarantee, so on strict-alignment targets the store bus-faults
and the cast violates strict aliasing. Write each word with
writeUnalignedWord32, which does an alignment-safe byte copy, matching
mldsa_encode_w1_88_c and the neighboring ML-KEM sampling code.

Fixes F-6782.
This commit is contained in:
Tobias Frauenschläger
2026-07-21 15:26:51 +02:00
parent ca449b1263
commit 097ddc19d8
1 changed files with 15 additions and 11 deletions
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wolfcrypt/src/wc_mlkem_poly.c
+15 -11
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@@ -5864,18 +5864,22 @@ static void mlkem_vec_compress_10_c(byte* r, sword16* v, unsigned int k)
sword16 t14 = TO_COMP_WORD_10(v, i, j, 14);
sword16 t15 = TO_COMP_WORD_10(v, i, j, 15);
word32* r32 = (word32*)r;
/* Pack sixteen 10-bit values into byte array. */
r32[0] = (word32)t0 | ((word32)t1 << 10) |
((word32)t2 << 20) | ((word32)t3 << 30);
r32[1] = ((word32)t3 >> 2) | ((word32)t4 << 8) |
((word32)t5 << 18) | ((word32)t6 << 28);
r32[2] = ((word32)t6 >> 4) | ((word32)t7 << 6) |
((word32)t8 << 16) | ((word32)t9 << 26);
r32[3] = ((word32)t9 >> 6) | ((word32)t10 << 4) |
((word32)t11 << 14) | ((word32)t12 << 24);
r32[4] = ((word32)t12 >> 8) | ((word32)t13 << 2) |
((word32)t14 << 12) | ((word32)t15 << 22);
writeUnalignedWord32(r + 0,
(word32)t0 | ((word32)t1 << 10) |
((word32)t2 << 20) | ((word32)t3 << 30));
writeUnalignedWord32(r + 4,
((word32)t3 >> 2) | ((word32)t4 << 8) |
((word32)t5 << 18) | ((word32)t6 << 28));
writeUnalignedWord32(r + 8,
((word32)t6 >> 4) | ((word32)t7 << 6) |
((word32)t8 << 16) | ((word32)t9 << 26));
writeUnalignedWord32(r + 12,
((word32)t9 >> 6) | ((word32)t10 << 4) |
((word32)t11 << 14) | ((word32)t12 << 24));
writeUnalignedWord32(r + 16,
((word32)t12 >> 8) | ((word32)t13 << 2) |
((word32)t14 << 12) | ((word32)t15 << 22));
/* Move over set bytes. */
r += 20;