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mpi_exp_mod: fix out of bounds access

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The table size was set before the configured window size bound was
applied which lead to out of bounds access when the configured window
size bound is less.

Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2022-11-22 10:18:06 +00:00
parent 9c09326572
commit 060009518b
1 changed files with 2 additions and 1 deletions
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3
library/bignum.c
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@ -2005,13 +2005,14 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
window_bitsize = ( i > 671 ) ? 6 : ( i > 239 ) ? 5 : window_bitsize = ( i > 671 ) ? 6 : ( i > 239 ) ? 5 :
( i > 79 ) ? 4 : ( i > 23 ) ? 3 : 1; ( i > 79 ) ? 4 : ( i > 23 ) ? 3 : 1;
const size_t w_table_used_size = ( (size_t)1 << window_bitsize ) + 1;
#if( MBEDTLS_MPI_WINDOW_SIZE < 6 ) #if( MBEDTLS_MPI_WINDOW_SIZE < 6 )
if( window_bitsize > MBEDTLS_MPI_WINDOW_SIZE ) if( window_bitsize > MBEDTLS_MPI_WINDOW_SIZE )
window_bitsize = MBEDTLS_MPI_WINDOW_SIZE; window_bitsize = MBEDTLS_MPI_WINDOW_SIZE;
#endif #endif
const size_t w_table_used_size = ( (size_t) 1 << window_bitsize ) + 1;
/* /*
* This function is not constant-trace: its memory accesses depend on the * This function is not constant-trace: its memory accesses depend on the
* exponent value. To defend against timing attacks, callers (such as RSA * exponent value. To defend against timing attacks, callers (such as RSA