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Fix Non CF access to table in base64 decrypt

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Signed-off-by: Paul Elliott <paul.elliott@arm.com>
This commit is contained in:
Paul Elliott 2021-03-01 19:15:43 +00:00
parent 6e152fa362
commit 0544d49330
1 changed files with 17 additions and 4 deletions
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21
library/base64.c
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@ -66,9 +66,9 @@ static const unsigned char base64_dec_map[128] =
#define BASE64_SIZE_T_MAX ( (size_t) -1 ) /* SIZE_T_MAX is not standard */ #define BASE64_SIZE_T_MAX ( (size_t) -1 ) /* SIZE_T_MAX is not standard */
/* /*
* Constant flow conditional assignment * Constant flow conditional assignment to unsigned char
*/ */
static void mbedtls_base64_cond_assign(unsigned char * dest, const unsigned char * const src, static void mbedtls_base64_cond_assign_uchar(unsigned char * dest, const unsigned char * const src,
unsigned char condition) unsigned char condition)
{ {
/* make sure assign is 0 or 1 in a time-constant manner */ /* make sure assign is 0 or 1 in a time-constant manner */
@ -77,6 +77,19 @@ static void mbedtls_base64_cond_assign(unsigned char * dest, const unsigned char
*dest = ( *dest ) * ( 1 - condition ) + ( *src ) * condition; *dest = ( *dest ) * ( 1 - condition ) + ( *src ) * condition;
} }
/*
* Constant flow conditional assignment to uint_32
*/
static void mbedtls_base64_cond_assign_uint32(uint32_t * dest, const uint32_t src,
unsigned char condition)
{
/* make sure assign is 0 or 1 in a time-constant manner */
condition = (condition | (unsigned char)-condition) >> 7;
*dest = ( *dest ) * ( 1 - condition ) + ( src ) * condition;
}
/* /*
* Constant flow check for equality * Constant flow check for equality
*/ */
@ -114,7 +127,7 @@ static unsigned char mbedtls_base64_table_lookup(const unsigned char * const tab
for( i = 0; i < table_size; ++i ) for( i = 0; i < table_size; ++i )
{ {
mbedtls_base64_cond_assign(&result, &table[i], mbedtls_base64_eq(i, table_index)); mbedtls_base64_cond_assign_uchar(&result, &table[i], mbedtls_base64_eq(i, table_index));
} }
return result; return result;
@ -275,7 +288,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
dec_map_lookup = mbedtls_base64_table_lookup(base64_dec_map, sizeof( base64_dec_map ), *src ); dec_map_lookup = mbedtls_base64_table_lookup(base64_dec_map, sizeof( base64_dec_map ), *src );
j -= ( dec_map_lookup == 64 ); mbedtls_base64_cond_assign_uint32( &j, j - 1, mbedtls_base64_eq( dec_map_lookup, 64 ) );
x = ( x << 6 ) | ( dec_map_lookup & 0x3F ); x = ( x << 6 ) | ( dec_map_lookup & 0x3F );
if( ++n == 4 ) if( ++n == 4 )