From 919925673d6c9cfed3c1085497f5dfbbed5fc431 Mon Sep 17 00:00:00 2001
From: Alex Chernyakhovsky <achernya@google.com>
Date: Thu, 16 Jun 2022 12:00:22 +1000
Subject: [PATCH] Fix AES OCB encrypt/decrypt for x86 AES-NI
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aesni_ocb_encrypt and aesni_ocb_decrypt operate by having a fast-path
that performs operations on 6 16-byte blocks concurrently (the
"grandloop") and then proceeds to handle the "short" tail (which can
be anywhere from 0 to 5 blocks) that remain.

As part of initialization, the assembly initializes $len to the true
length, less 96 bytes and converts it to a pointer so that the $inp
can be compared to it. Each iteration of "grandloop" checks to see if
there's a full 96-byte chunk to process, and if so, continues. Once
this has been exhausted, it falls through to "short", which handles
the remaining zero to five blocks.

Unfortunately, the jump at the end of "grandloop" had a fencepost
error, doing a `jb` ("jump below") rather than `jbe` (jump below or
equal). This should be `jbe`, as $inp is pointing to the *end* of the
chunk currently being handled. If $inp == $len, that means that
there's a whole 96-byte chunk waiting to be handled. If $inp > $len,
then there's 5 or fewer 16-byte blocks left to be handled, and the
fall-through is intended.

The net effect of `jb` instead of `jbe` is that the last 16-byte block
of the last 96-byte chunk was completely omitted. The contents of
`out` in this position were never written to. Additionally, since
those bytes were never processed, the authentication tag generated is
also incorrect.

The same fencepost error, and identical logic, exists in both
aesni_ocb_encrypt and aesni_ocb_decrypt.

This addresses CVE-2022-2097.

Co-authored-by: Alejandro Sedeño <asedeno@google.com>
Co-authored-by: David Benjamin <davidben@google.com>

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
---
 crypto/aes/asm/aesni-x86.pl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crypto/aes/asm/aesni-x86.pl b/crypto/aes/asm/aesni-x86.pl
index fe2b265..812758e 100644
--- a/crypto/aes/asm/aesni-x86.pl
+++ b/crypto/aes/asm/aesni-x86.pl
@@ -2027,7 +2027,7 @@ my ($l_,$block,$i1,$i3,$i5) = ($rounds_,$key_,$rounds,$len,$out);
 	&movdqu		(&QWP(-16*2,$out,$inp),$inout4);
 	&movdqu		(&QWP(-16*1,$out,$inp),$inout5);
 	&cmp		($inp,$len);			# done yet?
-	&jb		(&label("grandloop"));
+	&jbe		(&label("grandloop"));
 
 &set_label("short");
 	&add		($len,16*6);
@@ -2453,7 +2453,7 @@ my ($l_,$block,$i1,$i3,$i5) = ($rounds_,$key_,$rounds,$len,$out);
 	&pxor		($rndkey1,$inout5);
 	&movdqu		(&QWP(-16*1,$out,$inp),$inout5);
 	&cmp		($inp,$len);			# done yet?
-	&jb		(&label("grandloop"));
+	&jbe		(&label("grandloop"));
 
 &set_label("short");
 	&add		($len,16*6);
-- 
1.8.3.1