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Add x86-64 const-time assembly

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-05-12 12:11:37 +01:00
parent d395590597
commit 664fea481c
1 changed files with 47 additions and 0 deletions
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47
library/constant_time_impl.h
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@ -71,6 +71,8 @@
#define MBEDTLS_CT_ARM_ASM
#elif defined(__aarch64__)
#define MBEDTLS_CT_AARCH64_ASM
#elif defined(__amd64__) || defined(__x86_64__)
#define MBEDTLS_CT_X86_64_ASM
#endif
#endif
@ -175,6 +177,19 @@ static inline mbedtls_ct_condition_t mbedtls_ct_bool(mbedtls_ct_uint_t x)
"cc" /* clobbers flag bits */
);
return (mbedtls_ct_condition_t) x;
#elif defined(MBEDTLS_CT_X86_64_ASM) && (defined(MBEDTLS_CT_SIZE_32) || defined(MBEDTLS_CT_SIZE_64))
uint64_t s;
asm volatile ("mov %[x], %[s] \n\t"
"neg %[s] \n\t"
"or %[x], %[s] \n\t"
"sar $63, %[s] \n\t"
:
[s] "=&a" (s)
:
[x] "D" (x)
:
);
return (mbedtls_ct_condition_t) s;
#else
const mbedtls_ct_uint_t xo = mbedtls_ct_compiler_opaque(x);
#if defined(_MSC_VER)
@ -230,6 +245,19 @@ static inline mbedtls_ct_uint_t mbedtls_ct_if(mbedtls_ct_condition_t condition,
"cc"
);
return (mbedtls_ct_uint_t) condition;
#elif defined(MBEDTLS_CT_X86_64_ASM) && (defined(MBEDTLS_CT_SIZE_32) || defined(MBEDTLS_CT_SIZE_64))
asm volatile ("and %[condition], %[if1] \n\t"
"not %[condition] \n\t"
"and %[condition], %[if0] \n\t"
"or %[if1], %[if0] \n\t"
:
[condition] "+&D" (condition),
[if1] "+&S" (if1),
[if0] "+&a" (if0)
:
:
);
return if0;
#else
mbedtls_ct_condition_t not_cond =
(mbedtls_ct_condition_t) (~mbedtls_ct_compiler_opaque(condition));
@ -274,6 +302,25 @@ static inline mbedtls_ct_condition_t mbedtls_ct_uint_lt(mbedtls_ct_uint_t x, mbe
"cc"
);
return (mbedtls_ct_condition_t) x;
#elif defined(MBEDTLS_CT_X86_64_ASM) && (defined(MBEDTLS_CT_SIZE_32) || defined(MBEDTLS_CT_SIZE_64))
uint64_t mask;
asm volatile ("mov %[x], %[mask] \n\t"
"xor %[y], %[mask] \n\t"
"sub %[y], %[x] \n\t"
"and %[mask], %[y] \n\t"
"not %[mask] \n\t"
"and %[mask], %[x] \n\t"
"or %[y], %[x] \n\t"
"mov %[x], %[mask] \n\t"
"sar $63, %[mask] \n\t"
:
[mask] "=&a" (mask),
[x] "+&S" (x),
[y] "+&D" (y)
:
:
);
return (mbedtls_ct_condition_t) mask;
#else
/* Ensure that the compiler cannot optimise the following operations over x and y,
* even if it knows the value of x and y.