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| author | Anastasia Tishchenko <sv3iry@gmail.com> | 2026-05-13 13:57:40 +0300 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2026-05-22 20:25:29 +0800 |
| commit | 27b536a2ec8e2f85a0380c2d13c9ecbc7aaab406 (patch) | |
| tree | ad11c59e59430464ba82a95b3b0830e99a245b99 /crypto | |
| parent | 310bcf581dc57506160ef138ad6276e965b550cd (diff) | |
| download | linux-next-history-27b536a2ec8e2f85a0380c2d13c9ecbc7aaab406.tar.gz | |
crypto: ecc - Fix carry overflow in vli multiplication
The carry flag calculation fails when r01.m_high is saturated
(0xFFFFFFFFFFFFFFFF) and addition of lower bits overflows.
The condition (r01.m_high < product.m_high) doesn't handle the case
where r01.m_high == product.m_high and an additional carry exists
from lower-bit overflow.
When commit 3c4b23901a0c ("crypto: ecdh - Add ECDH software support")
introduced crypto/ecc.c, it split the muladd() function in the
micro-ecc library into separate mul_64_64() and add_128_128() helpers.
It seems the check got lost in translation.
Add proper handling for this boundary by accounting for the carry
from the lower addition.
Fixes: 3c4b23901a0c ("crypto: ecdh - Add ECDH software support")
Signed-off-by: Anastasia Tishchenko <sv3iry@gmail.com>
Cc: stable@vger.kernel.org # v4.8+
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto')
| -rw-r--r-- | crypto/ecc.c | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/crypto/ecc.c b/crypto/ecc.c index 43b0def3a225c..6eb4d97a5f0d3 100644 --- a/crypto/ecc.c +++ b/crypto/ecc.c @@ -393,14 +393,26 @@ static uint128_t mul_64_64(u64 left, u64 right) return result; } -static uint128_t add_128_128(uint128_t a, uint128_t b) +/* Calculate addition with overflow checking. Returns true on wrap-around, + * false otherwise. + */ +static bool check_add_128_128_overflow(uint128_t *result, uint128_t a, + uint128_t b) { - uint128_t result; + bool carry; - result.m_low = a.m_low + b.m_low; - result.m_high = a.m_high + b.m_high + (result.m_low < a.m_low); + result->m_low = a.m_low + b.m_low; + carry = (result->m_low < a.m_low); - return result; + result->m_high = a.m_high + b.m_high + carry; + + /* Using constant-time bitwise arithmetic to prevent timing + * side-channels. + */ + carry = (result->m_high < a.m_high) | + ((result->m_high == a.m_high) & carry); + + return carry; } static void vli_mult(u64 *result, const u64 *left, const u64 *right, @@ -425,9 +437,7 @@ static void vli_mult(u64 *result, const u64 *left, const u64 *right, uint128_t product; product = mul_64_64(left[i], right[k - i]); - - r01 = add_128_128(r01, product); - r2 += (r01.m_high < product.m_high); + r2 += check_add_128_128_overflow(&r01, r01, product); } result[k] = r01.m_low; @@ -450,7 +460,7 @@ static void vli_umult(u64 *result, const u64 *left, u32 right, uint128_t product; product = mul_64_64(left[k], right); - r01 = add_128_128(r01, product); + check_add_128_128_overflow(&r01, r01, product); /* no carry */ result[k] = r01.m_low; r01.m_low = r01.m_high; @@ -487,8 +497,7 @@ static void vli_square(u64 *result, const u64 *left, unsigned int ndigits) product.m_low <<= 1; } - r01 = add_128_128(r01, product); - r2 += (r01.m_high < product.m_high); + r2 += check_add_128_128_overflow(&r01, r01, product); } result[k] = r01.m_low; |