crypto: aesni - fix more FPU handling and indirect call issues

PATCH In review Ard Biesheuvel 2 participants 4 messages Jan 16, 2021 – Jan 22, 2021

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x86 Crypto API

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Ard Biesheuvel

author

2021-01-16 17:15 UTC #0 lore raw

cover crypto: aesni - fix more FPU handling and indirect call issues

My recent patches to the AES-NI driver addressed all the instances of indirect calls occurring in the XTS and GCM drivers, and while at it, limited the scope of FPU enabled/preemption disabled regions not to cover the work that goes on inside the skcipher walk API. This gets rid of scheduling latency spikes for large skcipher/aead inputs, which are more common these days after the introduction of s/w kTLS.

Let's address the other modes in this driver as well: ECB, CBC and CTR, all of which currently keep the FPU enabled (and thus preemption disabled) for the entire skcipher request, which is unnecessary, and potentially problematic for workloads that are sensitive to scheduling latency.

Let's also switch to a static call for the CTR mode asm helper, which gets chosen once at driver init time.

Cc Megha Dey <[email protected]>

Cc Eric Biggers <[email protected]>

Cc Herbert Xu <[email protected]>

Ard Biesheuvel (2):
crypto: aesni - replace CTR function pointer with static call
crypto: aesni - release FPU during skcipher walk API calls

 arch/x86/crypto/aesni-intel_glue.c | 78 +++++++++-----------
 1 file changed, 35 insertions(+), 43 deletions(-)

Signature · 1 line

2.17.1

Ard Biesheuvel

author

2021-01-16 17:15 UTC #1 lore raw

PATCH 1/2 crypto: aesni - replace CTR function pointer with static call

Indirect calls are very expensive on x86, so use a static call to set the system-wide AES-NI/CTR asm helper.

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

---
 arch/x86/crypto/aesni-intel_glue.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

arch/x86/crypto/aesni-intel_glue.c +7 -6

index a548fdbc3073..d96685457196 100644
@@ -34,6 +34,7 @@
 #include <linux/jump_label.h>
 #include <linux/workqueue.h>
 #include <linux/spinlock.h>
+#include <linux/static_call.h>
 
 
 #define AESNI_ALIGN	16

@@ -107,10 +108,9 @@ asmlinkage void aesni_xts_decrypt(const struct crypto_aes_ctx *ctx, u8 *out,
 
 #ifdef CONFIG_X86_64
 
-static void (*aesni_ctr_enc_tfm)(struct crypto_aes_ctx *ctx, u8 *out,
-			      const u8 *in, unsigned int len, u8 *iv);
 asmlinkage void aesni_ctr_enc(struct crypto_aes_ctx *ctx, u8 *out,
 			      const u8 *in, unsigned int len, u8 *iv);
+DEFINE_STATIC_CALL(aesni_ctr_enc_tfm, aesni_ctr_enc);
 
 /* Scatter / Gather routines, with args similar to above */
 asmlinkage void aesni_gcm_init(void *ctx,

@@ -520,8 +520,10 @@ static int ctr_crypt(struct skcipher_request *req)
 
 	kernel_fpu_begin();
 	while ((nbytes = walk.nbytes) >= AES_BLOCK_SIZE) {
-		aesni_ctr_enc_tfm(ctx, walk.dst.virt.addr, walk.src.virt.addr,
-			              nbytes & AES_BLOCK_MASK, walk.iv);
+		static_call(aesni_ctr_enc_tfm)(ctx, walk.dst.virt.addr,
+					       walk.src.virt.addr,
+					       nbytes & AES_BLOCK_MASK,
+					       walk.iv);
 		nbytes &= AES_BLOCK_SIZE - 1;
 		err = skcipher_walk_done(&walk, nbytes);
 	}

@@ -1160,10 +1162,9 @@ static int __init aesni_init(void)
 	} else {
 		pr_info("SSE version of gcm_enc/dec engaged.\n");
 	}
-	aesni_ctr_enc_tfm = aesni_ctr_enc;
 	if (boot_cpu_has(X86_FEATURE_AVX)) {
 		/* optimize performance of ctr mode encryption transform */
-		aesni_ctr_enc_tfm = aesni_ctr_enc_avx_tfm;
+		static_call_update(aesni_ctr_enc_tfm, aesni_ctr_enc_avx_tfm);
 		pr_info("AES CTR mode by8 optimization enabled\n");
 	}
 #endif

Signature · 1 line

2.17.1

Ard Biesheuvel

author

2021-01-16 17:15 UTC #2 lore raw

PATCH 2/2 crypto: aesni - release FPU during skcipher walk API calls

In reply to Ard Biesheuvel

Taking ownership of the FPU in kernel mode disables preemption, and this may result in excessive scheduling blackouts if the size of the data being processed on the FPU is unbounded.

Given that taking and releasing the FPU is cheap these days on x86, we can limit the impact of this issue easily for skcipher implementations, by moving the FPU begin/end calls inside the skcipher walk processing loop. Considering that skcipher walks operate on at most one page at a time, doing so fully mitigates this issue.

This also permits the skcipher walk logic to use non-atomic kmalloc() calls etc so we can change the 'atomic' bool argument in the calls to skcipher_walk_virt() to false as well.

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

---
 arch/x86/crypto/aesni-intel_glue.c | 73 +++++++++-----------
 1 file changed, 32 insertions(+), 41 deletions(-)

arch/x86/crypto/aesni-intel_glue.c +32 ~~-41~~

index d96685457196..2144e54a6c89 100644
@@ -283,16 +283,16 @@ static int ecb_encrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
-	kernel_fpu_begin();
 	while ((nbytes = walk.nbytes)) {
+		kernel_fpu_begin();
 		aesni_ecb_enc(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 			      nbytes & AES_BLOCK_MASK);
+		kernel_fpu_end();
 		nbytes &= AES_BLOCK_SIZE - 1;
 		err = skcipher_walk_done(&walk, nbytes);
 	}
-	kernel_fpu_end();
 
 	return err;
 }

@@ -305,16 +305,16 @@ static int ecb_decrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
-	kernel_fpu_begin();
 	while ((nbytes = walk.nbytes)) {
+		kernel_fpu_begin();
 		aesni_ecb_dec(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 			      nbytes & AES_BLOCK_MASK);
+		kernel_fpu_end();
 		nbytes &= AES_BLOCK_SIZE - 1;
 		err = skcipher_walk_done(&walk, nbytes);
 	}
-	kernel_fpu_end();
 
 	return err;
 }

@@ -327,16 +327,16 @@ static int cbc_encrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
-	kernel_fpu_begin();
 	while ((nbytes = walk.nbytes)) {
+		kernel_fpu_begin();
 		aesni_cbc_enc(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 			      nbytes & AES_BLOCK_MASK, walk.iv);
+		kernel_fpu_end();
 		nbytes &= AES_BLOCK_SIZE - 1;
 		err = skcipher_walk_done(&walk, nbytes);
 	}
-	kernel_fpu_end();
 
 	return err;
 }

@@ -349,16 +349,16 @@ static int cbc_decrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
-	kernel_fpu_begin();
 	while ((nbytes = walk.nbytes)) {
+		kernel_fpu_begin();
 		aesni_cbc_dec(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 			      nbytes & AES_BLOCK_MASK, walk.iv);
+		kernel_fpu_end();
 		nbytes &= AES_BLOCK_SIZE - 1;
 		err = skcipher_walk_done(&walk, nbytes);
 	}
-	kernel_fpu_end();
 
 	return err;
 }

@@ -476,21 +476,6 @@ static int cts_cbc_decrypt(struct skcipher_request *req)
 }
 
 #ifdef CONFIG_X86_64
-static void ctr_crypt_final(struct crypto_aes_ctx *ctx,
-			    struct skcipher_walk *walk)
-{
-	u8 *ctrblk = walk->iv;
-	u8 keystream[AES_BLOCK_SIZE];
-	u8 *src = walk->src.virt.addr;
-	u8 *dst = walk->dst.virt.addr;
-	unsigned int nbytes = walk->nbytes;
-
-	aesni_enc(ctx, keystream, ctrblk);
-	crypto_xor_cpy(dst, keystream, src, nbytes);
-
-	crypto_inc(ctrblk, AES_BLOCK_SIZE);
-}
-
 static void aesni_ctr_enc_avx_tfm(struct crypto_aes_ctx *ctx, u8 *out,
 			      const u8 *in, unsigned int len, u8 *iv)
 {

@@ -512,27 +497,33 @@ static int ctr_crypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct crypto_aes_ctx *ctx = aes_ctx(crypto_skcipher_ctx(tfm));
+	u8 keystream[AES_BLOCK_SIZE];
 	struct skcipher_walk walk;
 	unsigned int nbytes;
 	int err;
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
-	kernel_fpu_begin();
-	while ((nbytes = walk.nbytes) >= AES_BLOCK_SIZE) {
-		static_call(aesni_ctr_enc_tfm)(ctx, walk.dst.virt.addr,
-					       walk.src.virt.addr,
-					       nbytes & AES_BLOCK_MASK,
-					       walk.iv);
-		nbytes &= AES_BLOCK_SIZE - 1;
+	while ((nbytes = walk.nbytes) > 0) {
+		kernel_fpu_begin();
+		if (nbytes & AES_BLOCK_MASK)
+			static_call(aesni_ctr_enc_tfm)(ctx, walk.dst.virt.addr,
+						       walk.src.virt.addr,
+						       nbytes & AES_BLOCK_MASK,
+						       walk.iv);
+		nbytes &= ~AES_BLOCK_MASK;
+
+		if (walk.nbytes == walk.total && nbytes > 0) {
+			aesni_enc(ctx, keystream, walk.iv);
+			crypto_xor_cpy(walk.dst.virt.addr + walk.nbytes - nbytes,
+				       walk.src.virt.addr + walk.nbytes - nbytes,
+				       keystream, nbytes);
+			crypto_inc(walk.iv, AES_BLOCK_SIZE);
+			nbytes = 0;
+		}
+		kernel_fpu_end();
 		err = skcipher_walk_done(&walk, nbytes);
 	}
-	if (walk.nbytes) {
-		ctr_crypt_final(ctx, &walk);
-		err = skcipher_walk_done(&walk, 0);
-	}
-	kernel_fpu_end();
-
 	return err;
 }

Signature · 1 line

2.17.1

Herbert Xu

maintainer

2021-01-22 06:22 UTC #3 lore raw

In reply to Ard Biesheuvel

Quoted 19 lines · Ard Biesheuvel

My recent patches to the AES-NI driver addressed all the instances of indirect calls occurring in the XTS and GCM drivers, and while at it, limited the scope of FPU enabled/preemption disabled regions not to cover the work that goes on inside the skcipher walk API. This gets rid of scheduling latency spikes for large skcipher/aead inputs, which are more common these days after the introduction of s/w kTLS.
Let's address the other modes in this driver as well: ECB, CBC and CTR, all of which currently keep the FPU enabled (and thus preemption disabled) for the entire skcipher request, which is unnecessary, and potentially problematic for workloads that are sensitive to scheduling latency.
Let's also switch to a static call for the CTR mode asm helper, which gets chosen once at driver init time.
Cc Megha Dey <[email protected]>
Cc Eric Biggers <[email protected]>
Cc Herbert Xu <[email protected]>

Quoted 6 lines

Ard Biesheuvel (2):
crypto: aesni - replace CTR function pointer with static call
crypto: aesni - release FPU during skcipher walk API calls
 arch/x86/crypto/aesni-intel_glue.c | 78 +++++++++-----------
 1 file changed, 35 insertions(+), 43 deletions(-)

All 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