[PATCH v5 3/3] s390/crypto: Fix use of mutex in atomic context

[Harald Freudenberger <freude@linux.ibm.com>]

The AES CTR implementation used a mutex to lock one page of exclusive
memory for fast CTR processing. Unfortunately a mutex is not save to
use in atomic or interrupt context. So use a binary semaphore instead
which is save to use in such environments.

Furthermore rework the code to get rid of conditional locking. So
restructure the AES CRT code by extracting the main loop into a
separate function and just give in information about the (locked) page
can be used or not (is not locked).

Fixes: 7988fb2c03c8 ("crypto: s390/aes - convert to skcipher API")
Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Cc: stable@vger.kernel.org # 5.5+
---
 arch/s390/crypto/aes_s390.c | 63 +++++++++++++++++++++++--------------
 1 file changed, 39 insertions(+), 24 deletions(-)

diff --git a/arch/s390/crypto/aes_s390.c b/arch/s390/crypto/aes_s390.c
index 10561aa687c7..0be6fa779d2c 100644
--- a/arch/s390/crypto/aes_s390.c
+++ b/arch/s390/crypto/aes_s390.c
@@ -26,14 +26,14 @@
 #include <linux/module.h>
 #include <linux/cpufeature.h>
 #include <linux/init.h>
-#include <linux/mutex.h>
 #include <linux/fips.h>
+#include <linux/semaphore.h>
 #include <linux/string.h>
 #include <crypto/xts.h>
 #include <asm/cpacf.h>
 
 static u8 *ctrblk;
-static DEFINE_MUTEX(ctrblk_lock);
+static DEFINE_SEMAPHORE(ctrblk_sem, 1);
 
 static cpacf_mask_t km_functions, kmc_functions, kmctr_functions,
 		    kma_functions;
@@ -562,46 +562,61 @@ static unsigned int __ctrblk_init(u8 *ctrptr, u8 *iv, unsigned int nbytes)
 	return n;
 }
 
+static int __ctr_aes_crypt(struct s390_aes_ctx *sctx,
+			   struct skcipher_walk *walk, bool locked)
+{
+	unsigned int n, nbytes;
+	int ret = 0;
+	u8 *ctrptr;
+
+	while (!ret && ((nbytes = walk->nbytes) >= AES_BLOCK_SIZE)) {
+		n = AES_BLOCK_SIZE;
+		if (nbytes >= 2 * AES_BLOCK_SIZE && locked)
+			n = __ctrblk_init(ctrblk, walk->iv, nbytes);
+		ctrptr = (n > AES_BLOCK_SIZE) ? ctrblk : walk->iv;
+		cpacf_kmctr(sctx->fc, sctx->key, walk->dst.virt.addr,
+			    walk->src.virt.addr, n, ctrptr);
+		if (ctrptr == ctrblk)
+			memcpy(walk->iv, ctrptr + n - AES_BLOCK_SIZE,
+			       AES_BLOCK_SIZE);
+		crypto_inc(walk->iv, AES_BLOCK_SIZE);
+		ret = skcipher_walk_done(walk, nbytes - n);
+	}
+
+	return ret;
+}
+
 static int ctr_aes_crypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct s390_aes_ctx *sctx = crypto_skcipher_ctx(tfm);
-	u8 buf[AES_BLOCK_SIZE], *ctrptr;
 	struct skcipher_walk walk;
-	unsigned int n, nbytes;
-	int ret, locked;
+	u8 buf[AES_BLOCK_SIZE];
+	int ret;
 
 	if (unlikely(!sctx->fc))
 		return fallback_skcipher_crypt(sctx, req, 0);
 
-	locked = mutex_trylock(&ctrblk_lock);
-
 	ret = skcipher_walk_virt(&walk, req, false);
-	while (!ret && ((nbytes = walk.nbytes) >= AES_BLOCK_SIZE)) {
-		n = AES_BLOCK_SIZE;
+	if (ret)
+		return ret;
 
-		if (nbytes >= 2*AES_BLOCK_SIZE && locked)
-			n = __ctrblk_init(ctrblk, walk.iv, nbytes);
-		ctrptr = (n > AES_BLOCK_SIZE) ? ctrblk : walk.iv;
-		cpacf_kmctr(sctx->fc, sctx->key, walk.dst.virt.addr,
-			    walk.src.virt.addr, n, ctrptr);
-		if (ctrptr == ctrblk)
-			memcpy(walk.iv, ctrptr + n - AES_BLOCK_SIZE,
-			       AES_BLOCK_SIZE);
-		crypto_inc(walk.iv, AES_BLOCK_SIZE);
-		ret = skcipher_walk_done(&walk, nbytes - n);
+	if (down_trylock(&ctrblk_sem) == 0) {
+		ret = __ctr_aes_crypt(sctx, &walk, true);
+		up(&ctrblk_sem);
+	} else {
+		ret = __ctr_aes_crypt(sctx, &walk, false);
 	}
-	if (locked)
-		mutex_unlock(&ctrblk_lock);
+
 	/*
 	 * final block may be < AES_BLOCK_SIZE, copy only nbytes
 	 */
-	if (!ret && nbytes) {
+	if (!ret && walk.nbytes > 0) {
 		memset(buf, 0, AES_BLOCK_SIZE);
-		memcpy(buf, walk.src.virt.addr, nbytes);
+		memcpy(buf, walk.src.virt.addr, walk.nbytes);
 		cpacf_kmctr(sctx->fc, sctx->key, buf, buf,
 			    AES_BLOCK_SIZE, walk.iv);
-		memcpy(walk.dst.virt.addr, buf, nbytes);
+		memcpy(walk.dst.virt.addr, buf, walk.nbytes);
 		crypto_inc(walk.iv, AES_BLOCK_SIZE);
 		ret = skcipher_walk_done(&walk, 0);
 		memzero_explicit(buf, sizeof(buf));
-- 
2.43.0