crypto: aesni - fix counter overflow handling in "by8" variant

The "by8" CTR AVX implementation fails to propperly handle counter
overflows. That was the reason it got disabled in commit 7da4b29d496b
("crypto: aesni - disable "by8" AVX CTR optimization").

Fix the overflow handling by incrementing the counter block as a double
quad word, i.e. a 128 bit, and testing for overflows afterwards. We need
to use VPTEST to do so as VPADD* does not set the flags itself and
silently drops the carry bit.

As this change adds branches to the hot path, minor performance
regressions  might be a side effect. But, OTOH, we now have a conforming
implementation -- the preferable goal.

A tcrypt test on a SandyBridge system (i7-2620M) showed almost identical
numbers for the old and this version with differences within the noise
range. A dm-crypt test with the fixed version gave even slightly better
results for this version. So the performance impact might not be as big
as expected.

Tested-by: Romain Francoise <romain@orebokech.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Chandramouli Narayanan <mouli@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 15 insertions, 2 deletions

diff --git a/arch/x86/crypto/aes_ctrby8_avx-x86_64.S b/arch/x86/crypto/aes_ctrby8_avx-x86_64.S
index f091f122ed24..a029bc744244 100644
--- a/arch/x86/crypto/aes_ctrby8_avx-x86_64.S
+++ b/arch/x86/crypto/aes_ctrby8_avx-x86_64.S
@@ -108,6 +108,10 @@
 
 byteswap_const:
         .octa 0x000102030405060708090A0B0C0D0E0F
+ddq_low_msk:
+        .octa 0x0000000000000000FFFFFFFFFFFFFFFF
+ddq_high_add_1:
+        .octa 0x00000000000000010000000000000000
 ddq_add_1:
         .octa 0x00000000000000000000000000000001
 ddq_add_2:
@@ -169,7 +173,12 @@ ddq_add_8:
         .rept (by - 1)
                 club DDQ_DATA, i
                 club XDATA, i
-                vpaddd  var_ddq_add(%rip), xcounter, var_xdata
+                vpaddq  var_ddq_add(%rip), xcounter, var_xdata
+                vptest  ddq_low_msk(%rip), var_xdata
+                jnz 1f
+                vpaddq  ddq_high_add_1(%rip), var_xdata, var_xdata
+                vpaddq  ddq_high_add_1(%rip), xcounter, xcounter
+                1:
                 vpshufb xbyteswap, var_xdata, var_xdata
                 .set i, (i +1)
         .endr
@@ -178,7 +187,11 @@ ddq_add_8:
 
         vpxor   xkey0, xdata0, xdata0
         club DDQ_DATA, by
-        vpaddd  var_ddq_add(%rip), xcounter, xcounter
+        vpaddq  var_ddq_add(%rip), xcounter, xcounter
+        vptest  ddq_low_msk(%rip), xcounter
+        jnz     1f
+        vpaddq  ddq_high_add_1(%rip), xcounter, xcounter
+        1:
 
         .set i, 1
         .rept (by - 1)