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Fix signed left-shifts in curve25519.c.

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Due to a language flaw in C, left-shifts on signed integers are
undefined for negative numbers. This makes them all but useless. Cast to
the unsigned type, left-shift, and cast back (casts are defined to wrap)
to silence UBSan.

Change-Id: I8fbe739aee1c99cf553462b675863e6d68c2b302
Reviewed-on: https://boringssl-review.googlesource.com/c/34446
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2019-01-21 07:40:33 +00:00 committed by Adam Langley
parent fc27a1919c
commit 9847cdd785
1 changed files with 121 additions and 115 deletions
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236
third_party/fiat/curve25519.c vendored
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@ -1046,6 +1046,12 @@ static void ge_double_scalarmult_vartime(ge_p2 *r, const uint8_t *a,
}
}
// int64_lshift21 returns |a << 21| but is defined when shifting bits into the
// sign bit. This works around a language flaw in C.
static inline int64_t int64_lshift21(int64_t a) {
return (int64_t)((uint64_t)a << 21);
}
// The set of scalars is \Z/l
// where l = 2^252 + 27742317777372353535851937790883648493.
@ -1149,38 +1155,38 @@ void x25519_sc_reduce(uint8_t s[64]) {
carry6 = (s6 + (1 << 20)) >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry8 = (s8 + (1 << 20)) >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry10 = (s10 + (1 << 20)) >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry12 = (s12 + (1 << 20)) >> 21;
s13 += carry12;
s12 -= carry12 << 21;
s12 -= int64_lshift21(carry12);
carry14 = (s14 + (1 << 20)) >> 21;
s15 += carry14;
s14 -= carry14 << 21;
s14 -= int64_lshift21(carry14);
carry16 = (s16 + (1 << 20)) >> 21;
s17 += carry16;
s16 -= carry16 << 21;
s16 -= int64_lshift21(carry16);
carry7 = (s7 + (1 << 20)) >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry9 = (s9 + (1 << 20)) >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry11 = (s11 + (1 << 20)) >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
carry13 = (s13 + (1 << 20)) >> 21;
s14 += carry13;
s13 -= carry13 << 21;
s13 -= int64_lshift21(carry13);
carry15 = (s15 + (1 << 20)) >> 21;
s16 += carry15;
s15 -= carry15 << 21;
s15 -= int64_lshift21(carry15);
s5 += s17 * 666643;
s6 += s17 * 470296;
@ -1232,41 +1238,41 @@ void x25519_sc_reduce(uint8_t s[64]) {
carry0 = (s0 + (1 << 20)) >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry2 = (s2 + (1 << 20)) >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry4 = (s4 + (1 << 20)) >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry6 = (s6 + (1 << 20)) >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry8 = (s8 + (1 << 20)) >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry10 = (s10 + (1 << 20)) >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry1 = (s1 + (1 << 20)) >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry3 = (s3 + (1 << 20)) >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry5 = (s5 + (1 << 20)) >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry7 = (s7 + (1 << 20)) >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry9 = (s9 + (1 << 20)) >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry11 = (s11 + (1 << 20)) >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
s0 += s12 * 666643;
s1 += s12 * 470296;
@ -1278,40 +1284,40 @@ void x25519_sc_reduce(uint8_t s[64]) {
carry0 = s0 >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry1 = s1 >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry2 = s2 >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry3 = s3 >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry4 = s4 >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry5 = s5 >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry6 = s6 >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry7 = s7 >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry8 = s8 >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry9 = s9 >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry10 = s10 >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry11 = s11 >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
s0 += s12 * 666643;
s1 += s12 * 470296;
@ -1323,37 +1329,37 @@ void x25519_sc_reduce(uint8_t s[64]) {
carry0 = s0 >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry1 = s1 >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry2 = s2 >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry3 = s3 >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry4 = s4 >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry5 = s5 >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry6 = s6 >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry7 = s7 >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry8 = s8 >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry9 = s9 >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry10 = s10 >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
s[0] = s0 >> 0;
s[1] = s0 >> 8;
@ -1519,74 +1525,74 @@ static void sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
carry0 = (s0 + (1 << 20)) >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry2 = (s2 + (1 << 20)) >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry4 = (s4 + (1 << 20)) >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry6 = (s6 + (1 << 20)) >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry8 = (s8 + (1 << 20)) >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry10 = (s10 + (1 << 20)) >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry12 = (s12 + (1 << 20)) >> 21;
s13 += carry12;
s12 -= carry12 << 21;
s12 -= int64_lshift21(carry12);
carry14 = (s14 + (1 << 20)) >> 21;
s15 += carry14;
s14 -= carry14 << 21;
s14 -= int64_lshift21(carry14);
carry16 = (s16 + (1 << 20)) >> 21;
s17 += carry16;
s16 -= carry16 << 21;
s16 -= int64_lshift21(carry16);
carry18 = (s18 + (1 << 20)) >> 21;
s19 += carry18;
s18 -= carry18 << 21;
s18 -= int64_lshift21(carry18);
carry20 = (s20 + (1 << 20)) >> 21;
s21 += carry20;
s20 -= carry20 << 21;
s20 -= int64_lshift21(carry20);
carry22 = (s22 + (1 << 20)) >> 21;
s23 += carry22;
s22 -= carry22 << 21;
s22 -= int64_lshift21(carry22);
carry1 = (s1 + (1 << 20)) >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry3 = (s3 + (1 << 20)) >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry5 = (s5 + (1 << 20)) >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry7 = (s7 + (1 << 20)) >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry9 = (s9 + (1 << 20)) >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry11 = (s11 + (1 << 20)) >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
carry13 = (s13 + (1 << 20)) >> 21;
s14 += carry13;
s13 -= carry13 << 21;
s13 -= int64_lshift21(carry13);
carry15 = (s15 + (1 << 20)) >> 21;
s16 += carry15;
s15 -= carry15 << 21;
s15 -= int64_lshift21(carry15);
carry17 = (s17 + (1 << 20)) >> 21;
s18 += carry17;
s17 -= carry17 << 21;
s17 -= int64_lshift21(carry17);
carry19 = (s19 + (1 << 20)) >> 21;
s20 += carry19;
s19 -= carry19 << 21;
s19 -= int64_lshift21(carry19);
carry21 = (s21 + (1 << 20)) >> 21;
s22 += carry21;
s21 -= carry21 << 21;
s21 -= int64_lshift21(carry21);
s11 += s23 * 666643;
s12 += s23 * 470296;
@ -1638,38 +1644,38 @@ static void sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
carry6 = (s6 + (1 << 20)) >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry8 = (s8 + (1 << 20)) >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry10 = (s10 + (1 << 20)) >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry12 = (s12 + (1 << 20)) >> 21;
s13 += carry12;
s12 -= carry12 << 21;
s12 -= int64_lshift21(carry12);
carry14 = (s14 + (1 << 20)) >> 21;
s15 += carry14;
s14 -= carry14 << 21;
s14 -= int64_lshift21(carry14);
carry16 = (s16 + (1 << 20)) >> 21;
s17 += carry16;
s16 -= carry16 << 21;
s16 -= int64_lshift21(carry16);
carry7 = (s7 + (1 << 20)) >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry9 = (s9 + (1 << 20)) >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry11 = (s11 + (1 << 20)) >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
carry13 = (s13 + (1 << 20)) >> 21;
s14 += carry13;
s13 -= carry13 << 21;
s13 -= int64_lshift21(carry13);
carry15 = (s15 + (1 << 20)) >> 21;
s16 += carry15;
s15 -= carry15 << 21;
s15 -= int64_lshift21(carry15);
s5 += s17 * 666643;
s6 += s17 * 470296;
@ -1721,41 +1727,41 @@ static void sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
carry0 = (s0 + (1 << 20)) >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry2 = (s2 + (1 << 20)) >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry4 = (s4 + (1 << 20)) >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry6 = (s6 + (1 << 20)) >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry8 = (s8 + (1 << 20)) >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry10 = (s10 + (1 << 20)) >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry1 = (s1 + (1 << 20)) >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry3 = (s3 + (1 << 20)) >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry5 = (s5 + (1 << 20)) >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry7 = (s7 + (1 << 20)) >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry9 = (s9 + (1 << 20)) >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry11 = (s11 + (1 << 20)) >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
s0 += s12 * 666643;
s1 += s12 * 470296;
@ -1767,40 +1773,40 @@ static void sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
carry0 = s0 >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry1 = s1 >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry2 = s2 >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry3 = s3 >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry4 = s4 >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry5 = s5 >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry6 = s6 >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry7 = s7 >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry8 = s8 >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry9 = s9 >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry10 = s10 >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
carry11 = s11 >> 21;
s12 += carry11;
s11 -= carry11 << 21;
s11 -= int64_lshift21(carry11);
s0 += s12 * 666643;
s1 += s12 * 470296;
@ -1812,37 +1818,37 @@ static void sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
carry0 = s0 >> 21;
s1 += carry0;
s0 -= carry0 << 21;
s0 -= int64_lshift21(carry0);
carry1 = s1 >> 21;
s2 += carry1;
s1 -= carry1 << 21;
s1 -= int64_lshift21(carry1);
carry2 = s2 >> 21;
s3 += carry2;
s2 -= carry2 << 21;
s2 -= int64_lshift21(carry2);
carry3 = s3 >> 21;
s4 += carry3;
s3 -= carry3 << 21;
s3 -= int64_lshift21(carry3);
carry4 = s4 >> 21;
s5 += carry4;
s4 -= carry4 << 21;
s4 -= int64_lshift21(carry4);
carry5 = s5 >> 21;
s6 += carry5;
s5 -= carry5 << 21;
s5 -= int64_lshift21(carry5);
carry6 = s6 >> 21;
s7 += carry6;
s6 -= carry6 << 21;
s6 -= int64_lshift21(carry6);
carry7 = s7 >> 21;
s8 += carry7;
s7 -= carry7 << 21;
s7 -= int64_lshift21(carry7);
carry8 = s8 >> 21;
s9 += carry8;
s8 -= carry8 << 21;
s8 -= int64_lshift21(carry8);
carry9 = s9 >> 21;
s10 += carry9;
s9 -= carry9 << 21;
s9 -= int64_lshift21(carry9);
carry10 = s10 >> 21;
s11 += carry10;
s10 -= carry10 << 21;
s10 -= int64_lshift21(carry10);
s[0] = s0 >> 0;
s[1] = s0 >> 8;