crypto: x86/chacha-sse3 - use unaligned loads for state array

PATCH In review Ard Biesheuvel 4 participants 4 messages Jul 8, 2020 – Jul 16, 2020

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x86 Crypto API

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Ard Biesheuvel

author

2020-07-08 09:11 UTC #0 lore raw

PATCH 1/1 crypto: x86/chacha-sse3 - use unaligned loads for state array

Due to the fact that the x86 port does not support allocating objects on the stack with an alignment that exceeds 8 bytes, we have a rather ugly hack in the x86 code for ChaCha to ensure that the state array is aligned to 16 bytes, allowing the SSE3 implementation of the algorithm to use aligned loads.

Given that the performance benefit of using of aligned loads appears to be limited (~0.25% for 1k blocks using tcrypt on a Corei7-8650U), and the fact that this hack has leaked into generic ChaCha code, let's just remove it.

Cc Martin Willi <[email protected]>

Cc Herbert Xu <[email protected]>

Cc Eric Biggers <[email protected]>

Signed-off-by Ard Biesheuvel <[email protected]>

---
 arch/x86/crypto/chacha-ssse3-x86_64.S | 16 ++++++++--------
 arch/x86/crypto/chacha_glue.c         | 17 ++---------------
 include/crypto/chacha.h               |  4 ----
 3 files changed, 10 insertions(+), 27 deletions(-)

arch/x86/crypto/chacha-ssse3-x86_64.S +8 -8

index a38ab2512a6f..ca1788bfee16 100644
@@ -120,10 +120,10 @@ SYM_FUNC_START(chacha_block_xor_ssse3)
 	FRAME_BEGIN
 
 	# x0..3 = s0..3
-	movdqa		0x00(%rdi),%xmm0
-	movdqa		0x10(%rdi),%xmm1
-	movdqa		0x20(%rdi),%xmm2
-	movdqa		0x30(%rdi),%xmm3
+	movdqu		0x00(%rdi),%xmm0
+	movdqu		0x10(%rdi),%xmm1
+	movdqu		0x20(%rdi),%xmm2
+	movdqu		0x30(%rdi),%xmm3
 	movdqa		%xmm0,%xmm8
 	movdqa		%xmm1,%xmm9
 	movdqa		%xmm2,%xmm10

@@ -205,10 +205,10 @@ SYM_FUNC_START(hchacha_block_ssse3)
 	# %edx: nrounds
 	FRAME_BEGIN
 
-	movdqa		0x00(%rdi),%xmm0
-	movdqa		0x10(%rdi),%xmm1
-	movdqa		0x20(%rdi),%xmm2
-	movdqa		0x30(%rdi),%xmm3
+	movdqu		0x00(%rdi),%xmm0
+	movdqu		0x10(%rdi),%xmm1
+	movdqu		0x20(%rdi),%xmm2
+	movdqu		0x30(%rdi),%xmm3
 
 	mov		%edx,%r8d
 	call		chacha_permute

arch/x86/crypto/chacha_glue.c +2 ~~-15~~

index 22250091cdbe..e67a59130025 100644
@@ -14,8 +14,6 @@
 #include <linux/module.h>
 #include <asm/simd.h>
 
-#define CHACHA_STATE_ALIGN 16
-
 asmlinkage void chacha_block_xor_ssse3(u32 *state, u8 *dst, const u8 *src,
 				       unsigned int len, int nrounds);
 asmlinkage void chacha_4block_xor_ssse3(u32 *state, u8 *dst, const u8 *src,

@@ -124,8 +122,6 @@ static void chacha_dosimd(u32 *state, u8 *dst, const u8 *src,
 
 void hchacha_block_arch(const u32 *state, u32 *stream, int nrounds)
 {
-	state = PTR_ALIGN(state, CHACHA_STATE_ALIGN);
-
 	if (!static_branch_likely(&chacha_use_simd) || !crypto_simd_usable()) {
 		hchacha_block_generic(state, stream, nrounds);
 	} else {

@@ -138,8 +134,6 @@ EXPORT_SYMBOL(hchacha_block_arch);
 
 void chacha_init_arch(u32 *state, const u32 *key, const u8 *iv)
 {
-	state = PTR_ALIGN(state, CHACHA_STATE_ALIGN);
-
 	chacha_init_generic(state, key, iv);
 }
 EXPORT_SYMBOL(chacha_init_arch);

@@ -147,8 +141,6 @@ EXPORT_SYMBOL(chacha_init_arch);
 void chacha_crypt_arch(u32 *state, u8 *dst, const u8 *src, unsigned int bytes,
 		       int nrounds)
 {
-	state = PTR_ALIGN(state, CHACHA_STATE_ALIGN);
-
 	if (!static_branch_likely(&chacha_use_simd) || !crypto_simd_usable() ||
 	    bytes <= CHACHA_BLOCK_SIZE)
 		return chacha_crypt_generic(state, dst, src, bytes, nrounds);

@@ -170,15 +162,12 @@ EXPORT_SYMBOL(chacha_crypt_arch);
 static int chacha_simd_stream_xor(struct skcipher_request *req,
 				  const struct chacha_ctx *ctx, const u8 *iv)
 {
-	u32 *state, state_buf[16 + 2] __aligned(8);
+	u32 state[CHACHA_STATE_WORDS] __aligned(8);
 	struct skcipher_walk walk;
 	int err;
 
 	err = skcipher_walk_virt(&walk, req, false);
 
-	BUILD_BUG_ON(CHACHA_STATE_ALIGN != 16);
-	state = PTR_ALIGN(state_buf + 0, CHACHA_STATE_ALIGN);
-
 	chacha_init_generic(state, ctx->key, iv);
 
 	while (walk.nbytes > 0) {

@@ -217,12 +206,10 @@ static int xchacha_simd(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
-	u32 *state, state_buf[16 + 2] __aligned(8);
+	u32 state[CHACHA_STATE_WORDS] __aligned(8);
 	struct chacha_ctx subctx;
 	u8 real_iv[16];
 
-	BUILD_BUG_ON(CHACHA_STATE_ALIGN != 16);
-	state = PTR_ALIGN(state_buf + 0, CHACHA_STATE_ALIGN);
 	chacha_init_generic(state, ctx->key, req->iv);
 
 	if (req->cryptlen > CHACHA_BLOCK_SIZE && crypto_simd_usable()) {

include/crypto/chacha.h +0 -4

index 2676f4fbd4c1..3a1c72fdb7cf 100644
@@ -25,11 +25,7 @@
 #define CHACHA_BLOCK_SIZE	64
 #define CHACHAPOLY_IV_SIZE	12
 
-#ifdef CONFIG_X86_64
-#define CHACHA_STATE_WORDS	((CHACHA_BLOCK_SIZE + 12) / sizeof(u32))
-#else
 #define CHACHA_STATE_WORDS	(CHACHA_BLOCK_SIZE / sizeof(u32))
-#endif
 
 /* 192-bit nonce, then 64-bit stream position */
 #define XCHACHA_IV_SIZE		32

Signature · 1 line

2.17.1

Martin Willi

Reviewed-by on v1 1/1

2020-07-08 11:56 UTC #1 lore raw

Quoted 11 lines

Due to the fact that the x86 port does not support allocating objects on the stack with an alignment that exceeds 8 bytes, we have a rather ugly hack in the x86 code for ChaCha to ensure that the state array is aligned to 16 bytes, allowing the SSE3 implementation of the algorithm to use aligned loads.
Given that the performance benefit of using of aligned loads appears to be limited (~0.25% for 1k blocks using tcrypt on a Corei7-8650U), and the fact that this hack has leaked into generic ChaCha code, let's just remove it.

Reviewed-by Martin Willi <[email protected]>

Thanks,
Martin

Eric Biggers

Reviewed-by on v1 1/1

2020-07-08 16:19 UTC #2 lore raw

In reply to Ard Biesheuvel

Quoted 11 lines · Ard Biesheuvel

Due to the fact that the x86 port does not support allocating objects on the stack with an alignment that exceeds 8 bytes, we have a rather ugly hack in the x86 code for ChaCha to ensure that the state array is aligned to 16 bytes, allowing the SSE3 implementation of the algorithm to use aligned loads.
Given that the performance benefit of using of aligned loads appears to be limited (~0.25% for 1k blocks using tcrypt on a Corei7-8650U), and the fact that this hack has leaked into generic ChaCha code, let's just remove it.

Quoted 4 lines

Cc Martin Willi <[email protected]>
Cc Herbert Xu <[email protected]>
Cc Eric Biggers <[email protected]>
Signed-off-by Ard Biesheuvel <[email protected]>

Reviewed-by Eric Biggers <[email protected]>

Herbert Xu

maintainer

2020-07-16 11:54 UTC #3 lore raw

In reply to Ard Biesheuvel

Quoted 15 lines · Ard Biesheuvel

Due to the fact that the x86 port does not support allocating objects on the stack with an alignment that exceeds 8 bytes, we have a rather ugly hack in the x86 code for ChaCha to ensure that the state array is aligned to 16 bytes, allowing the SSE3 implementation of the algorithm to use aligned loads.
Given that the performance benefit of using of aligned loads appears to be limited (~0.25% for 1k blocks using tcrypt on a Corei7-8650U), and the fact that this hack has leaked into generic ChaCha code, let's just remove it.
Cc Martin Willi <[email protected]>
Cc Herbert Xu <[email protected]>
Cc Eric Biggers <[email protected]>
Signed-off-by Ard Biesheuvel <[email protected]>

Quoted 5 lines

---
 arch/x86/crypto/chacha-ssse3-x86_64.S | 16 ++++++++--------
 arch/x86/crypto/chacha_glue.c         | 17 ++---------------
 include/crypto/chacha.h               |  4 ----
 3 files changed, 10 insertions(+), 27 deletions(-)

Patch applied. Thanks.

Signature · 3 lines

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt