bn/asm/x86_64-mont5.pl: fix carry bug in bn_sqrx8x_internal.
authorAndy Polyakov <appro@openssl.org>
Thu, 17 Aug 2017 19:08:57 +0000 (21:08 +0200)
committerMatt Caswell <matt@openssl.org>
Thu, 2 Nov 2017 11:00:48 +0000 (11:00 +0000)
Credit to OSS-Fuzz for finding this.

CVE-2017-3736

Reviewed-by: Rich Salz <rsalz@openssl.org>
crypto/bn/asm/x86_64-mont5.pl

index 9c77642..1666fbd 100755 (executable)
@@ -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