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bn/asm/x86_64-mont5.pl: fix carry bug in bn_sqrx8x_internal.

Credit to OSS-Fuzz for finding this.

CVE-2017-3736

Reviewed-by: Rich Salz <rsalz@openssl.org>
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dot-asm authored and mattcaswell committed Aug 17, 2017
1 parent b701fa8 commit 4443cf7aa0099e5ce615c18cee249fff77fb0871
Showing with 10 additions and 2 deletions.
  1. +10 −2 crypto/bn/asm/x86_64-mont5.pl
@@ -3099,11 +3099,19 @@
.align 32
.Lsqrx8x_break:
sub 16+8(%rsp),%r8 # consume last carry
xor $zero,$zero
sub 16+8(%rsp),%rbx # mov 16(%rsp),%cf
adcx $zero,%r8
mov 24+8(%rsp),$carry # initial $tptr, borrow $carry
adcx $zero,%r9
mov 0*8($aptr),%rdx # a[8], modulo-scheduled
xor %ebp,%ebp # xor $zero,$zero
adc \$0,%r10
mov %r8,0*8($tptr)
adc \$0,%r11
adc \$0,%r12
adc \$0,%r13
adc \$0,%r14
adc \$0,%r15
cmp $carry,$tptr # cf=0, of=0
je .Lsqrx8x_outer_loop

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