[PATCH AUTOSEL 4.20 032/304] crypto: aes_ti - disable interrupts while accessing S-box

[PATCH AUTOSEL 4.20 032/304] crypto: aes_ti - disable interrupts while accessing S-box

[Sasha Levin]

From: Eric Biggers <ebiggers@google.com>

[ Upstream commit 0a6a40c2a8c184a2fb467efacfb1cd338d719e0b ]

In the "aes-fixed-time" AES implementation, disable interrupts while
accessing the S-box, in order to make cache-timing attacks more
difficult.  Previously it was possible for the CPU to be interrupted
while the S-box was loaded into L1 cache, potentially evicting the
cachelines and causing later table lookups to be time-variant.

In tests I did on x86 and ARM, this doesn't affect performance
significantly.  Responsiveness is potentially a concern, but interrupts
are only disabled for a single AES block.

Note that even after this change, the implementation still isn't
necessarily guaranteed to be constant-time; see
https://cr.yp.to/antiforgery/cachetiming-20050414.pdf for a discussion
of the many difficulties involved in writing truly constant-time AES
software.  But it's valuable to make such attacks more difficult.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 crypto/Kconfig  |  3 ++-
 crypto/aes_ti.c | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 05c91eb10ca1..4f24acac3d48 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1006,7 +1006,8 @@ config CRYPTO_AES_TI
 	  8 for decryption), this implementation only uses just two S-boxes of
 	  256 bytes each, and attempts to eliminate data dependent latencies by
 	  prefetching the entire table into the cache at the start of each
-	  block.
+	  block. Interrupts are also disabled to avoid races where cachelines
+	  are evicted when the CPU is interrupted to do something else.
 
 config CRYPTO_AES_586
 	tristate "AES cipher algorithms (i586)"
diff --git a/crypto/aes_ti.c b/crypto/aes_ti.c
index 03023b2290e8..1ff9785b30f5 100644
--- a/crypto/aes_ti.c
+++ b/crypto/aes_ti.c
@@ -269,6 +269,7 @@ static void aesti_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	const u32 *rkp = ctx->key_enc + 4;
 	int rounds = 6 + ctx->key_length / 4;
 	u32 st0[4], st1[4];
+	unsigned long flags;
 	int round;
 
 	st0[0] = ctx->key_enc[0] ^ get_unaligned_le32(in);
@@ -276,6 +277,12 @@ static void aesti_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	st0[2] = ctx->key_enc[2] ^ get_unaligned_le32(in + 8);
 	st0[3] = ctx->key_enc[3] ^ get_unaligned_le32(in + 12);
 
+	/*
+	 * Temporarily disable interrupts to avoid races where cachelines are
+	 * evicted when the CPU is interrupted to do something else.
+	 */
+	local_irq_save(flags);
+
 	st0[0] ^= __aesti_sbox[ 0] ^ __aesti_sbox[128];
 	st0[1] ^= __aesti_sbox[32] ^ __aesti_sbox[160];
 	st0[2] ^= __aesti_sbox[64] ^ __aesti_sbox[192];
@@ -300,6 +307,8 @@ static void aesti_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	put_unaligned_le32(subshift(st1, 1) ^ rkp[5], out + 4);
 	put_unaligned_le32(subshift(st1, 2) ^ rkp[6], out + 8);
 	put_unaligned_le32(subshift(st1, 3) ^ rkp[7], out + 12);
+
+	local_irq_restore(flags);
 }
 
 static void aesti_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
@@ -308,6 +317,7 @@ static void aesti_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	const u32 *rkp = ctx->key_dec + 4;
 	int rounds = 6 + ctx->key_length / 4;
 	u32 st0[4], st1[4];
+	unsigned long flags;
 	int round;
 
 	st0[0] = ctx->key_dec[0] ^ get_unaligned_le32(in);
@@ -315,6 +325,12 @@ static void aesti_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	st0[2] = ctx->key_dec[2] ^ get_unaligned_le32(in + 8);
 	st0[3] = ctx->key_dec[3] ^ get_unaligned_le32(in + 12);
 
+	/*
+	 * Temporarily disable interrupts to avoid races where cachelines are
+	 * evicted when the CPU is interrupted to do something else.
+	 */
+	local_irq_save(flags);
+
 	st0[0] ^= __aesti_inv_sbox[ 0] ^ __aesti_inv_sbox[128];
 	st0[1] ^= __aesti_inv_sbox[32] ^ __aesti_inv_sbox[160];
 	st0[2] ^= __aesti_inv_sbox[64] ^ __aesti_inv_sbox[192];
@@ -339,6 +355,8 @@ static void aesti_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 	put_unaligned_le32(inv_subshift(st1, 1) ^ rkp[5], out + 4);
 	put_unaligned_le32(inv_subshift(st1, 2) ^ rkp[6], out + 8);
 	put_unaligned_le32(inv_subshift(st1, 3) ^ rkp[7], out + 12);
+
+	local_irq_restore(flags);
 }
 
 static struct crypto_alg aes_alg = {
-- 
2.19.1

[PATCH AUTOSEL 4.20 266/304] crypto: ux500 - Use proper enum in cryp_set_dma_transfer

[Sasha Levin]

From: Nathan Chancellor <natechancellor@gmail.com>

[ Upstream commit 9d880c5945c748d8edcac30965f3349a602158c4 ]

Clang warns when one enumerated type is implicitly converted to another:

drivers/crypto/ux500/cryp/cryp_core.c:559:5: warning: implicit
conversion from enumeration type 'enum dma_data_direction' to different
enumeration type 'enum dma_transfer_direction' [-Wenum-conversion]
                                direction, DMA_CTRL_ACK);
                                ^~~~~~~~~
drivers/crypto/ux500/cryp/cryp_core.c:583:5: warning: implicit
conversion from enumeration type 'enum dma_data_direction' to different
enumeration type 'enum dma_transfer_direction' [-Wenum-conversion]
                                direction,
                                ^~~~~~~~~
2 warnings generated.

dmaengine_prep_slave_sg expects an enum from dma_transfer_direction.
Because we know the value of the dma_data_direction enum from the
switch statement, we can just use the proper value from
dma_transfer_direction so there is no more conversion.

DMA_TO_DEVICE = DMA_MEM_TO_DEV = 1
DMA_FROM_DEVICE = DMA_DEV_TO_MEM = 2

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/crypto/ux500/cryp/cryp_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/ux500/cryp/cryp_core.c b/drivers/crypto/ux500/cryp/cryp_core.c
index d2663a4e1f5e..a92a66b1ff46 100644
--- a/drivers/crypto/ux500/cryp/cryp_core.c
+++ b/drivers/crypto/ux500/cryp/cryp_core.c
@@ -556,7 +556,7 @@ static int cryp_set_dma_transfer(struct cryp_ctx *ctx,
 		desc = dmaengine_prep_slave_sg(channel,
 				ctx->device->dma.sg_src,
 				ctx->device->dma.sg_src_len,
-				direction, DMA_CTRL_ACK);
+				DMA_MEM_TO_DEV, DMA_CTRL_ACK);
 		break;
 
 	case DMA_FROM_DEVICE:
@@ -580,7 +580,7 @@ static int cryp_set_dma_transfer(struct cryp_ctx *ctx,
 		desc = dmaengine_prep_slave_sg(channel,
 				ctx->device->dma.sg_dst,
 				ctx->device->dma.sg_dst_len,
-				direction,
+				DMA_DEV_TO_MEM,
 				DMA_CTRL_ACK |
 				DMA_PREP_INTERRUPT);
 
-- 
2.19.1

[PATCH AUTOSEL 4.20 267/304] crypto: ux500 - Use proper enum in hash_set_dma_transfer

[Sasha Levin]

From: Nathan Chancellor <natechancellor@gmail.com>

[ Upstream commit 5ac93f808338f4dd465402e91869702eb87db241 ]

Clang warns when one enumerated type is implicitly converted to another:

drivers/crypto/ux500/hash/hash_core.c:169:4: warning: implicit
conversion from enumeration type 'enum dma_data_direction' to different
enumeration type 'enum dma_transfer_direction' [-Wenum-conversion]
                        direction, DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
                        ^~~~~~~~~
1 warning generated.

dmaengine_prep_slave_sg expects an enum from dma_transfer_direction.
We know that the only direction supported by this function is
DMA_TO_DEVICE because of the check at the top of this function so we can
just use the equivalent value from dma_transfer_direction.

DMA_TO_DEVICE = DMA_MEM_TO_DEV = 1

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/crypto/ux500/hash/hash_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/crypto/ux500/hash/hash_core.c b/drivers/crypto/ux500/hash/hash_core.c
index 633321a8dd03..a0bb8a6eec3f 100644
--- a/drivers/crypto/ux500/hash/hash_core.c
+++ b/drivers/crypto/ux500/hash/hash_core.c
@@ -166,7 +166,7 @@ static int hash_set_dma_transfer(struct hash_ctx *ctx, struct scatterlist *sg,
 		__func__);
 	desc = dmaengine_prep_slave_sg(channel,
 			ctx->device->dma.sg, ctx->device->dma.sg_len,
-			direction, DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
+			DMA_MEM_TO_DEV, DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
 	if (!desc) {
 		dev_err(ctx->device->dev,
 			"%s: dmaengine_prep_slave_sg() failed!\n", __func__);
-- 
2.19.1