[RFC PATCH 2/7] crypto: x86/sha - limit FPU preemption

[Robert Elliott]

As done by the ECB and CBC helpers in arch/x86/crypt/ecb_cbc_helpers.h,
limit the number of bytes processed between kernel_fpu_begin() and
kernel_fpu_end() calls.

Those functions call preempt_disable() and preempt_enable(), so
the CPU core is unavailable for scheduling while running.

This leads to "rcu_preempt detected expedited stalls" with stack dumps
pointing to the optimized hash function if this module is loaded and
used a lot:
    rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: {12-... } 22 jiffies s: 277 root: 0x1/.

For example, that can occur during boot with the stack track pointing
to the sha512-x86 function if the system set to use SHA-512 for
module signing. The call trace includes:
    module_sig_check
    mod_verify_sig
    pkcs7_verify
    pkcs7_digest
    sha512_finup
    sha512_base_do_update

Fixes: 66be89515888 ("crypto: sha1 - SSSE3 based SHA1 implementation for x86-64")
Fixes: 8275d1aa6422 ("crypto: sha256 - Create module providing optimized SHA256 routines using SSSE3, AVX or AVX2 instructions.")
Fixes: 87de4579f92d ("crypto: sha512 - Create module providing optimized SHA512 routines using SSSE3, AVX or AVX2 instructions.")
Fixes: aa031b8f702e ("crypto: x86/sha512 - load based on CPU features")
Suggested-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Robert Elliott <elliott@xxxxxxx>
---
 arch/x86/crypto/sha1_ssse3_glue.c   | 34 +++++++++++++++++++++++-----
 arch/x86/crypto/sha256_ssse3_glue.c | 35 ++++++++++++++++++++++++-----
 arch/x86/crypto/sha512_ssse3_glue.c | 35 ++++++++++++++++++++++++-----
 3 files changed, 89 insertions(+), 15 deletions(-)

diff --git a/arch/x86/crypto/sha1_ssse3_glue.c b/arch/x86/crypto/sha1_ssse3_glue.c
index 4430463dee62..033812989476 100644
--- a/arch/x86/crypto/sha1_ssse3_glue.c
+++ b/arch/x86/crypto/sha1_ssse3_glue.c
@@ -27,10 +27,13 @@
 #include <asm/cpu_device_id.h>
 #include <asm/simd.h>
 
+#define FPU_BYTES 4096U /* avoid kernel_fpu_begin/end scheduler/rcu stalls */
+
 static int sha1_update(struct shash_desc *desc, const u8 *data,
 			     unsigned int len, sha1_block_fn *sha1_xform)
 {
 	struct sha1_state *sctx = shash_desc_ctx(desc);
+	unsigned int chunk;
 
 	if (!crypto_simd_usable() ||
 	    (sctx->count % SHA1_BLOCK_SIZE) + len < SHA1_BLOCK_SIZE)
@@ -42,9 +45,18 @@ static int sha1_update(struct shash_desc *desc, const u8 *data,
 	 */
 	BUILD_BUG_ON(offsetof(struct sha1_state, state) != 0);
 
-	kernel_fpu_begin();
-	sha1_base_do_update(desc, data, len, sha1_xform);
-	kernel_fpu_end();
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha1_base_do_update(desc, data, chunk, sha1_xform);
+			kernel_fpu_end();
+		}
+
+		data += chunk;
+	} while (len);
 
 	return 0;
 }
@@ -52,12 +64,24 @@ static int sha1_update(struct shash_desc *desc, const u8 *data,
 static int sha1_finup(struct shash_desc *desc, const u8 *data,
 		      unsigned int len, u8 *out, sha1_block_fn *sha1_xform)
 {
+	unsigned int chunk;
+
 	if (!crypto_simd_usable())
 		return crypto_sha1_finup(desc, data, len, out);
 
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha1_base_do_update(desc, data, chunk, sha1_xform);
+			kernel_fpu_end();
+		}
+		data += chunk;
+	} while (len);
+
 	kernel_fpu_begin();
-	if (len)
-		sha1_base_do_update(desc, data, len, sha1_xform);
 	sha1_base_do_finalize(desc, sha1_xform);
 	kernel_fpu_end();
 
diff --git a/arch/x86/crypto/sha256_ssse3_glue.c b/arch/x86/crypto/sha256_ssse3_glue.c
index e437fba0299b..99a25c238f40 100644
--- a/arch/x86/crypto/sha256_ssse3_glue.c
+++ b/arch/x86/crypto/sha256_ssse3_glue.c
@@ -40,6 +40,8 @@
 #include <asm/cpu_device_id.h>
 #include <asm/simd.h>
 
+#define FPU_BYTES 4096U /* avoid kernel_fpu_begin/end scheduler/rcu stalls */
+
 asmlinkage void sha256_transform_ssse3(struct sha256_state *state,
 				       const u8 *data, int blocks);
 
@@ -47,6 +49,7 @@ static int _sha256_update(struct shash_desc *desc, const u8 *data,
 			  unsigned int len, sha256_block_fn *sha256_xform)
 {
 	struct sha256_state *sctx = shash_desc_ctx(desc);
+	unsigned int chunk;
 
 	if (!crypto_simd_usable() ||
 	    (sctx->count % SHA256_BLOCK_SIZE) + len < SHA256_BLOCK_SIZE)
@@ -58,9 +61,18 @@ static int _sha256_update(struct shash_desc *desc, const u8 *data,
 	 */
 	BUILD_BUG_ON(offsetof(struct sha256_state, state) != 0);
 
-	kernel_fpu_begin();
-	sha256_base_do_update(desc, data, len, sha256_xform);
-	kernel_fpu_end();
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha256_base_do_update(desc, data, chunk, sha256_xform);
+			kernel_fpu_end();
+		}
+
+		data += chunk;
+	} while (len);
 
 	return 0;
 }
@@ -68,12 +80,25 @@ static int _sha256_update(struct shash_desc *desc, const u8 *data,
 static int sha256_finup(struct shash_desc *desc, const u8 *data,
 	      unsigned int len, u8 *out, sha256_block_fn *sha256_xform)
 {
+	unsigned int chunk;
+
 	if (!crypto_simd_usable())
 		return crypto_sha256_finup(desc, data, len, out);
 
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha256_base_do_update(desc, data, chunk, sha256_xform);
+			kernel_fpu_end();
+		}
+
+		data += chunk;
+	} while (len);
+
 	kernel_fpu_begin();
-	if (len)
-		sha256_base_do_update(desc, data, len, sha256_xform);
 	sha256_base_do_finalize(desc, sha256_xform);
 	kernel_fpu_end();
 
diff --git a/arch/x86/crypto/sha512_ssse3_glue.c b/arch/x86/crypto/sha512_ssse3_glue.c
index 3c19f803f288..72eee03448dc 100644
--- a/arch/x86/crypto/sha512_ssse3_glue.c
+++ b/arch/x86/crypto/sha512_ssse3_glue.c
@@ -39,6 +39,8 @@
 #include <asm/cpu_device_id.h>
 #include <asm/simd.h>
 
+#define FPU_BYTES 4096U /* avoid kernel_fpu_begin/end scheduler/rcu stalls */
+
 asmlinkage void sha512_transform_ssse3(struct sha512_state *state,
 				       const u8 *data, int blocks);
 
@@ -46,6 +48,7 @@ static int sha512_update(struct shash_desc *desc, const u8 *data,
 		       unsigned int len, sha512_block_fn *sha512_xform)
 {
 	struct sha512_state *sctx = shash_desc_ctx(desc);
+	unsigned int chunk;
 
 	if (!crypto_simd_usable() ||
 	    (sctx->count[0] % SHA512_BLOCK_SIZE) + len < SHA512_BLOCK_SIZE)
@@ -57,9 +60,18 @@ static int sha512_update(struct shash_desc *desc, const u8 *data,
 	 */
 	BUILD_BUG_ON(offsetof(struct sha512_state, state) != 0);
 
-	kernel_fpu_begin();
-	sha512_base_do_update(desc, data, len, sha512_xform);
-	kernel_fpu_end();
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha512_base_do_update(desc, data, chunk, sha512_xform);
+			kernel_fpu_end();
+		}
+
+		data += chunk;
+	} while (len);
 
 	return 0;
 }
@@ -67,12 +79,25 @@ static int sha512_update(struct shash_desc *desc, const u8 *data,
 static int sha512_finup(struct shash_desc *desc, const u8 *data,
 	      unsigned int len, u8 *out, sha512_block_fn *sha512_xform)
 {
+	unsigned int chunk;
+
 	if (!crypto_simd_usable())
 		return crypto_sha512_finup(desc, data, len, out);
 
+	do {
+		chunk = min(len, FPU_BYTES);
+		len -= chunk;
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sha512_base_do_update(desc, data, chunk, sha512_xform);
+			kernel_fpu_end();
+		}
+
+		data += chunk;
+	} while (len);
+
 	kernel_fpu_begin();
-	if (len)
-		sha512_base_do_update(desc, data, len, sha512_xform);
 	sha512_base_do_finalize(desc, sha512_xform);
 	kernel_fpu_end();
 
-- 
2.37.3