Hi
I've compiled a recent SNAP of OpenSSL 1.0.1 (from 18/12). I am pretty sure
that the assembly language code generated for the ghash function (in
ghash-x86.s) is incorrect.
The gcm_init_4bit() function generates a 16-entry table of 128-bit values, to
be used as a multiplication table. The first value is always zero, while the
others usually aren't.
The supposedly equivalent gcm_init_clmul() function does not touch indexes 2-16
of the table, and pushes two usually non-zero entries into the first two
entries of the table.
Notice how %edx holds a pointer to the Htable, while %eax holds a pointer to H.
The final two lines of the function put a value in the first ((%edx)) and
second (16(%edx)) positions of the table. Clearly, this is wrong.
.globl gcm_init_clmul
.type gcm_init_clmul,@function
.align 16
gcm_init_clmul:
.L_gcm_init_clmul_begin:
movl 4(%esp),%edx
movl 8(%esp),%eax
call .L010pic
.L010pic:
popl %ecx
leal .Lbswap-.L010pic(%ecx),%ecx
movdqu (%eax),%xmm2
pshufd $78,%xmm2,%xmm2
pshufd $255,%xmm2,%xmm4
movdqa %xmm2,%xmm3
psllq $1,%xmm2
pxor %xmm5,%xmm5
psrlq $63,%xmm3
pcmpgtd %xmm4,%xmm5
pslldq $8,%xmm3
por %xmm3,%xmm2
pand 16(%ecx),%xmm5
pxor %xmm5,%xmm2
movdqa %xmm2,%xmm0
movdqa %xmm0,%xmm1
pshufd $78,%xmm0,%xmm3
pshufd $78,%xmm2,%xmm4
pxor %xmm0,%xmm3
pxor %xmm2,%xmm4
.byte 102,15,58,68,194,0
.byte 102,15,58,68,202,17
.byte 102,15,58,68,220,0
xorps %xmm0,%xmm3
xorps %xmm1,%xmm3
movdqa %xmm3,%xmm4
psrldq $8,%xmm3
pslldq $8,%xmm4
pxor %xmm3,%xmm1
pxor %xmm4,%xmm0
movdqa %xmm0,%xmm3
psllq $1,%xmm0
pxor %xmm3,%xmm0
psllq $5,%xmm0
pxor %xmm3,%xmm0
psllq $57,%xmm0
movdqa %xmm0,%xmm4
pslldq $8,%xmm0
psrldq $8,%xmm4
pxor %xmm3,%xmm0
pxor %xmm4,%xmm1
movdqa %xmm0,%xmm4
psrlq $5,%xmm0
pxor %xmm4,%xmm0
psrlq $1,%xmm0
pxor %xmm4,%xmm0
pxor %xmm1,%xmm4
psrlq $1,%xmm0
pxor %xmm4,%xmm0
movdqu %xmm2,(%edx)
movdqu %xmm0,16(%edx)
ret
.size gcm_init_clmul,.-.L_gcm_init_clmul_begin
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