On Sat, Jan 14, 2012 at 11:08:45AM -0800, Linus Torvalds wrote: > On Sat, Jan 14, 2012 at 10:40 AM, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote: > > > > Line by line explanation: > > * BLEND_OP > > array is "circular" now, all indexes have to be modulo 16. > > Round number is positive, so remainder operation should be > > without surprises. > > Don't use "%" except on unsigned values. Even if it's positive, if > it's a signed number and the compiler doesn't *see* that it is > absolutely positive, division is nontrivial. Even when you divide by a > constant. > > For example, "% 16" on an 'int' on x86-64 will generate > > movl %edi, %edx > sarl $31, %edx > shrl $28, %edx > leal (%rdi,%rdx), %eax > andl $15, %eax > subl %edx, %eax > > in order to get the signed case right. The fact that the end result is > correct for unsigned numbers is irrelevant: it's still stupid and > slow. > > With an unsigned int, '% 16' will generate the obvious > > andl $15, %eax > > instead. > > Quite frankly, stop using division in the first place. Dividing by > powers-of-two and expecting the compiler to fix things up is just > stupid, *exactly* because of issues like these: you either have to > think about it carefully, or the compiler may end up creating crap > code. For the record, it generates "andl $15" here. > So just use "& 15" instead. That doesn't have these kinds of issues. > It is a *good* thing when the C code is close to the end result you > want to generate. It is *not* a good thing to write code that looks > nothing like the end result and just expect the compiler to do the > right thing. Even if the compiler does do the right thing, what was > the advantage? Here is updated patch which explicitly uses & (equally tested): --------------------------------------------------------------- For rounds 16--79, W[i] only depends on W[i - 2], W[i - 7], W[i - 15] and W[i - 16]. Consequently, keeping all W[80] array on stack is unnecessary, only 16 values are really needed. Using W[16] instead of W[80] greatly reduces stack usage (~750 bytes to ~340 bytes on x86_64). Line by line explanation: * BLEND_OP array is "circular" now, all indexes have to be modulo 16. * initial full message scheduling is trimmed to first 16 values which come from data block, the rest is calculated right before it's needed. * original loop body is unrolled version of new SHA512_0_15 and SHA512_16_79 macros, unrolling was done to not do explicit variable renaming. Otherwise it's the very same code after preprocessing. See sha1_transform() code which does the same trick. Patch survives in-tree crypto test and original bugreport test (ping flood with hmac(sha512). See FIPS 180-2 for SHA-512 definition http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- This is patch is for stable if 750 byte stack usage is not considered safe. crypto/sha512_generic.c | 58 ++++++++++++++++++++++++++++-------------------- 1 file changed, 34 insertions(+), 24 deletions(-) --- a/crypto/sha512_generic.c +++ b/crypto/sha512_generic.c @@ -78,7 +78,7 @@ static inline void LOAD_OP(int I, u64 *W, const u8 *input) static inline void BLEND_OP(int I, u64 *W) { - W[I] = s1(W[I-2]) + W[I-7] + s0(W[I-15]) + W[I-16]; + W[I & 15] += s1(W[(I-2) & 15]) + W[(I-7) & 15] + s0(W[(I-15) & 15]); } static void @@ -87,38 +87,48 @@ sha512_transform(u64 *state, const u8 *input) u64 a, b, c, d, e, f, g, h, t1, t2; int i; - u64 W[80]; + u64 W[16]; /* load the input */ for (i = 0; i < 16; i++) LOAD_OP(i, W, input); - for (i = 16; i < 80; i++) { - BLEND_OP(i, W); - } - /* load the state into our registers */ a=state[0]; b=state[1]; c=state[2]; d=state[3]; e=state[4]; f=state[5]; g=state[6]; h=state[7]; - /* now iterate */ - for (i=0; i<80; i+=8) { - t1 = h + e1(e) + Ch(e,f,g) + sha512_K[i ] + W[i ]; - t2 = e0(a) + Maj(a,b,c); d+=t1; h=t1+t2; - t1 = g + e1(d) + Ch(d,e,f) + sha512_K[i+1] + W[i+1]; - t2 = e0(h) + Maj(h,a,b); c+=t1; g=t1+t2; - t1 = f + e1(c) + Ch(c,d,e) + sha512_K[i+2] + W[i+2]; - t2 = e0(g) + Maj(g,h,a); b+=t1; f=t1+t2; - t1 = e + e1(b) + Ch(b,c,d) + sha512_K[i+3] + W[i+3]; - t2 = e0(f) + Maj(f,g,h); a+=t1; e=t1+t2; - t1 = d + e1(a) + Ch(a,b,c) + sha512_K[i+4] + W[i+4]; - t2 = e0(e) + Maj(e,f,g); h+=t1; d=t1+t2; - t1 = c + e1(h) + Ch(h,a,b) + sha512_K[i+5] + W[i+5]; - t2 = e0(d) + Maj(d,e,f); g+=t1; c=t1+t2; - t1 = b + e1(g) + Ch(g,h,a) + sha512_K[i+6] + W[i+6]; - t2 = e0(c) + Maj(c,d,e); f+=t1; b=t1+t2; - t1 = a + e1(f) + Ch(f,g,h) + sha512_K[i+7] + W[i+7]; - t2 = e0(b) + Maj(b,c,d); e+=t1; a=t1+t2; +#define SHA512_0_15(i, a, b, c, d, e, f, g, h) \ + t1 = h + e1(e) + Ch(e, f, g) + sha512_K[i] + W[i]; \ + t2 = e0(a) + Maj(a, b, c); \ + d += t1; \ + h = t1 + t2 + +#define SHA512_16_79(i, a, b, c, d, e, f, g, h) \ + BLEND_OP(i, W); \ + t1 = h + e1(e) + Ch(e, f, g) + sha512_K[i] + W[(i)&15]; \ + t2 = e0(a) + Maj(a, b, c); \ + d += t1; \ + h = t1 + t2 + + for (i = 0; i < 16; i += 8) { + SHA512_0_15(i, a, b, c, d, e, f, g, h); + SHA512_0_15(i + 1, h, a, b, c, d, e, f, g); + SHA512_0_15(i + 2, g, h, a, b, c, d, e, f); + SHA512_0_15(i + 3, f, g, h, a, b, c, d, e); + SHA512_0_15(i + 4, e, f, g, h, a, b, c, d); + SHA512_0_15(i + 5, d, e, f, g, h, a, b, c); + SHA512_0_15(i + 6, c, d, e, f, g, h, a, b); + SHA512_0_15(i + 7, b, c, d, e, f, g, h, a); + } + for (i = 16; i < 80; i += 8) { + SHA512_16_79(i, a, b, c, d, e, f, g, h); + SHA512_16_79(i + 1, h, a, b, c, d, e, f, g); + SHA512_16_79(i + 2, g, h, a, b, c, d, e, f); + SHA512_16_79(i + 3, f, g, h, a, b, c, d, e); + SHA512_16_79(i + 4, e, f, g, h, a, b, c, d); + SHA512_16_79(i + 5, d, e, f, g, h, a, b, c); + SHA512_16_79(i + 6, c, d, e, f, g, h, a, b); + SHA512_16_79(i + 7, b, c, d, e, f, g, h, a); } state[0] += a; state[1] += b; state[2] += c; state[3] += d; -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
