diff options
| -rw-r--r-- | lib/crypto/gf128mul.c | 58 |
1 files changed, 39 insertions, 19 deletions
diff --git a/lib/crypto/gf128mul.c b/lib/crypto/gf128mul.c index a69ae3e6c16c..8f8c45e0cdcf 100644 --- a/lib/crypto/gf128mul.c +++ b/lib/crypto/gf128mul.c @@ -146,6 +146,17 @@ static void gf128mul_x8_lle(be128 *x) x->a = cpu_to_be64((a >> 8) ^ (_tt << 48)); } +/* time invariant version of gf128mul_x8_lle */ +static void gf128mul_x8_lle_ti(be128 *x) +{ + u64 a = be64_to_cpu(x->a); + u64 b = be64_to_cpu(x->b); + u64 _tt = xda_le(b & 0xff); /* avoid table lookup */ + + x->b = cpu_to_be64((b >> 8) | (a << 56)); + x->a = cpu_to_be64((a >> 8) ^ (_tt << 48)); +} + static void gf128mul_x8_bbe(be128 *x) { u64 a = be64_to_cpu(x->a); @@ -169,38 +180,47 @@ EXPORT_SYMBOL(gf128mul_x8_ble); void gf128mul_lle(be128 *r, const be128 *b) { - be128 p[8]; + /* + * The p array should be aligned to twice the size of its element type, + * so that every even/odd pair is guaranteed to share a cacheline + * (assuming a cacheline size of 32 bytes or more, which is by far the + * most common). This ensures that each be128_xor() call in the loop + * takes the same amount of time regardless of the value of 'ch', which + * is derived from function parameter 'b', which is commonly used as a + * key, e.g., for GHASH. The odd array elements are all set to zero, + * making each be128_xor() a NOP if its associated bit in 'ch' is not + * set, and this is equivalent to calling be128_xor() conditionally. + * This approach aims to avoid leaking information about such keys + * through execution time variances. + * + * Unfortunately, __aligned(16) or higher does not work on x86 for + * variables on the stack so we need to perform the alignment by hand. + */ + be128 array[16 + 3] = {}; + be128 *p = PTR_ALIGN(&array[0], 2 * sizeof(be128)); int i; p[0] = *r; for (i = 0; i < 7; ++i) - gf128mul_x_lle(&p[i + 1], &p[i]); + gf128mul_x_lle(&p[2 * i + 2], &p[2 * i]); memset(r, 0, sizeof(*r)); for (i = 0;;) { u8 ch = ((u8 *)b)[15 - i]; - if (ch & 0x80) - be128_xor(r, r, &p[0]); - if (ch & 0x40) - be128_xor(r, r, &p[1]); - if (ch & 0x20) - be128_xor(r, r, &p[2]); - if (ch & 0x10) - be128_xor(r, r, &p[3]); - if (ch & 0x08) - be128_xor(r, r, &p[4]); - if (ch & 0x04) - be128_xor(r, r, &p[5]); - if (ch & 0x02) - be128_xor(r, r, &p[6]); - if (ch & 0x01) - be128_xor(r, r, &p[7]); + be128_xor(r, r, &p[ 0 + !(ch & 0x80)]); + be128_xor(r, r, &p[ 2 + !(ch & 0x40)]); + be128_xor(r, r, &p[ 4 + !(ch & 0x20)]); + be128_xor(r, r, &p[ 6 + !(ch & 0x10)]); + be128_xor(r, r, &p[ 8 + !(ch & 0x08)]); + be128_xor(r, r, &p[10 + !(ch & 0x04)]); + be128_xor(r, r, &p[12 + !(ch & 0x02)]); + be128_xor(r, r, &p[14 + !(ch & 0x01)]); if (++i >= 16) break; - gf128mul_x8_lle(r); + gf128mul_x8_lle_ti(r); /* use the time invariant version */ } } EXPORT_SYMBOL(gf128mul_lle); |