bn/asm/x86_64-mont5.pl: fix carry bug in bn_sqrx8x_internal.
Credit to OSS-Fuzz for finding this.
CVE-2017-3736
@@ -3206,11 +3206,19 @@ $code.=<<___;
.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
