Re: [PATCH 2/2] crypto: arm/aes - don't use IV buffer to return final keystream block

[Herbert Xu]

On Thu, Feb 02, 2017 at 11:38:56AM +, Ard Biesheuvel wrote:
> The ARM bit sliced AES core code uses the IV buffer to pass the final
> keystream block back to the glue code if the input is not a multiple of
> the block size, so that the asm code does not have to deal with anything
> except 16 byte blocks. This is done under the assumption that the outgoing
> IV is meaningless anyway in this case, given that chaining is no longer
> possible under these circumstances.
> 
> However, as it turns out, the CCM driver does expect the IV to retain
> a value that is equal to the original IV except for the counter value,
> and even interprets byte zero as a length indicator, which may result
> in memory corruption if the IV is overwritten with something else.
> 
> So use a separate buffer to return the final keystream block.
> 
> Signed-off-by: Ard Biesheuvel 

Patch applied.  Thanks.
-- 
Email: Herbert Xu 
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

[PATCH 2/2] crypto: arm/aes - don't use IV buffer to return final keystream block

[Ard Biesheuvel]

The ARM bit sliced AES core code uses the IV buffer to pass the final
keystream block back to the glue code if the input is not a multiple of
the block size, so that the asm code does not have to deal with anything
except 16 byte blocks. This is done under the assumption that the outgoing
IV is meaningless anyway in this case, given that chaining is no longer
possible under these circumstances.

However, as it turns out, the CCM driver does expect the IV to retain
a value that is equal to the original IV except for the counter value,
and even interprets byte zero as a length indicator, which may result
in memory corruption if the IV is overwritten with something else.

So use a separate buffer to return the final keystream block.

Signed-off-by: Ard Biesheuvel 
---
 arch/arm/crypto/aes-neonbs-core.S | 16 +---
 arch/arm/crypto/aes-neonbs-glue.c |  9 +
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/arch/arm/crypto/aes-neonbs-core.S 
b/arch/arm/crypto/aes-neonbs-core.S
index c9477044fbba..2764edc56467 100644
--- a/arch/arm/crypto/aes-neonbs-core.S
+++ b/arch/arm/crypto/aes-neonbs-core.S
@@ -779,14 +779,15 @@ ENDPROC(aesbs_cbc_decrypt)
 
/*
 * aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
-*   int rounds, int blocks, u8 ctr[], bool final)
+*   int rounds, int blocks, u8 ctr[], u8 final[])
 */
 ENTRY(aesbs_ctr_encrypt)
mov ip, sp
push{r4-r10, lr}
 
ldm ip, {r5-r7} // load args 4-6
-   add r5, r5, r7  // one extra block if final == 1
+   teq r7, #0
+   addne   r5, r5, #1  // one extra block if final != 0
 
vld1.8  {q0}, [r6]  // load counter
vrev32.8q1, q0
@@ -865,19 +866,20 @@ ENTRY(aesbs_ctr_encrypt)
veorq2, q2, q14
vst1.8  {q2}, [r0]!
teq r4, #0  // skip last block if 'final'
-   W(bne)  4f
+   W(bne)  5f
 3: veorq5, q5, q15
vst1.8  {q5}, [r0]!
 
-   next_ctrq0
+4: next_ctrq0
 
subsr5, r5, #8
bgt 99b
 
-   vmovq5, q0
-
-4: vst1.8  {q5}, [r6]
+   vst1.8  {q0}, [r6]
pop {r4-r10, pc}
+
+5: vst1.8  {q5}, [r4]
+   b   4b
 ENDPROC(aesbs_ctr_encrypt)
 
.macro  next_tweak, out, in, const, tmp
diff --git a/arch/arm/crypto/aes-neonbs-glue.c 
b/arch/arm/crypto/aes-neonbs-glue.c
index e262f99a44d3..2920b96dbd36 100644
--- a/arch/arm/crypto/aes-neonbs-glue.c
+++ b/arch/arm/crypto/aes-neonbs-glue.c
@@ -35,7 +35,7 @@ asmlinkage void aesbs_cbc_decrypt(u8 out[], u8 const in[], u8 
const rk[],
  int rounds, int blocks, u8 iv[]);
 
 asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
- int rounds, int blocks, u8 ctr[], bool final);
+ int rounds, int blocks, u8 ctr[], u8 final[]);
 
 asmlinkage void aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[],
  int rounds, int blocks, u8 iv[]);
@@ -186,6 +186,7 @@ static int ctr_encrypt(struct skcipher_request *req)
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct aesbs_ctx *ctx = crypto_skcipher_ctx(tfm);
struct skcipher_walk walk;
+   u8 buf[AES_BLOCK_SIZE];
int err;
 
err = skcipher_walk_virt(, req, true);
@@ -193,12 +194,12 @@ static int ctr_encrypt(struct skcipher_request *req)
kernel_neon_begin();
while (walk.nbytes > 0) {
unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;
-   bool final = (walk.total % AES_BLOCK_SIZE) != 0;
+   u8 *final = (walk.total % AES_BLOCK_SIZE) ? buf : NULL;
 
if (walk.nbytes < walk.total) {
blocks = round_down(blocks,
walk.stride / AES_BLOCK_SIZE);
-   final = false;
+   final = NULL;
}
 
aesbs_ctr_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
@@ -210,7 +211,7 @@ static int ctr_encrypt(struct skcipher_request *req)
 
if (dst != src)
memcpy(dst, src, walk.total % AES_BLOCK_SIZE);
-   crypto_xor(dst, walk.iv, walk.total % AES_BLOCK_SIZE);
+   crypto_xor(dst, final, walk.total % AES_BLOCK_SIZE);
 
err = skcipher_walk_done(, 0);
break;
-- 
2.7.4