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Add x86 const-time assembly

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-05-13 12:32:09 +01:00
parent 664fea481c
commit 81673bba77
1 changed files with 47 additions and 0 deletions
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47
library/constant_time_impl.h
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@ -73,6 +73,8 @@
#define MBEDTLS_CT_AARCH64_ASM
#elif defined(__amd64__) || defined(__x86_64__)
#define MBEDTLS_CT_X86_64_ASM
#elif defined(__i386__)
#define MBEDTLS_CT_X86_ASM
#endif
#endif
@ -190,6 +192,19 @@ static inline mbedtls_ct_condition_t mbedtls_ct_bool(mbedtls_ct_uint_t x)
:
);
return (mbedtls_ct_condition_t) s;
#elif defined(MBEDTLS_CT_X86_ASM) && defined(MBEDTLS_CT_SIZE_32)
uint32_t s;
asm volatile ("mov %[x], %[s] \n\t"
"neg %[s] \n\t"
"or %[s], %[x] \n\t"
"sar $31, %[x] \n\t"
:
[s] "=&c" (s),
[x] "+&a" (x)
:
:
);
return (mbedtls_ct_condition_t) x;
#else
const mbedtls_ct_uint_t xo = mbedtls_ct_compiler_opaque(x);
#if defined(_MSC_VER)
@ -258,6 +273,19 @@ static inline mbedtls_ct_uint_t mbedtls_ct_if(mbedtls_ct_condition_t condition,
:
);
return if0;
#elif defined(MBEDTLS_CT_X86_ASM) && defined(MBEDTLS_CT_SIZE_32)
asm volatile ("and %[condition], %[if1] \n\t"
"not %[condition] \n\t"
"and %[if0], %[condition] \n\t"
"or %[condition], %[if1] \n\t"
:
[condition] "+&c" (condition),
[if1] "+&a" (if1)
:
[if0] "b" (if0)
:
);
return if1;
#else
mbedtls_ct_condition_t not_cond =
(mbedtls_ct_condition_t) (~mbedtls_ct_compiler_opaque(condition));
@ -321,6 +349,25 @@ static inline mbedtls_ct_condition_t mbedtls_ct_uint_lt(mbedtls_ct_uint_t x, mbe
:
);
return (mbedtls_ct_condition_t) mask;
#elif defined(MBEDTLS_CT_X86_ASM) && defined(MBEDTLS_CT_SIZE_32)
uint32_t s;
asm volatile ("mov %[x], %[s] \n\t"
"xor %[y], %[s] \n\t"
"sub %[y], %[x] \n\t"
"not %[s] \n\t"
"and %[s], %[x] \n\t"
"not %[s] \n\t"
"and %[y], %[s] \n\t"
"or %[s], %[x] \n\t"
"sar $31, %[x] \n\t"
:
[s] "=&b" (s),
[x] "+&a" (x)
:
[y] "c" (y)
:
);
return (mbedtls_ct_condition_t) x;
#else
/* Ensure that the compiler cannot optimise the following operations over x and y,
* even if it knows the value of x and y.