[PATCH] dm-integrity: reduce stack usage for recheck

[Mikulas Patocka <mpatocka@redhat.com>]

From: Arnd Bergmann <arnd@arndb.de>

The newly added integrity_recheck() function has another larger stack
allocation, just like its caller integrity_metadata(). When it gets
inlined, the combination of the two exceeds the warning limit for 32-bit
architectures and possibly risks an overflow when this is called from
a deep call chain through a file system:

drivers/md/dm-integrity.c:1767:13: error: stack frame size (1048) exceeds limit (1024) in 'integrity_metadata' [-Werror,-Wframe-larger-than]
 1767 | static void integrity_metadata(struct work_struct *w)

Since the caller at this point is done using its checksum buffer,
just reuse the same buffer in the new function to avoid the double
allocation.

Mikulas: I also added "noinline" to integrity_recheck and verity_recheck. 
These functions are only called on error, so they shouldn't bloat the 
stack frame or code size of the caller.

Fixes: c88f5e553fe3 ("dm-integrity: recheck the integrity tag after a failure")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-integrity.c     |    9 ++++-----
 drivers/md/dm-verity-target.c |    4 ++--
 2 files changed, 6 insertions(+), 7 deletions(-)

Index: linux-2.6/drivers/md/dm-integrity.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-integrity.c	2024-02-24 13:53:02.000000000 +0100
+++ linux-2.6/drivers/md/dm-integrity.c	2024-02-24 13:54:17.000000000 +0100
@@ -1691,14 +1691,13 @@ failed:
 	get_random_bytes(result, ic->tag_size);
 }
 
-static void integrity_recheck(struct dm_integrity_io *dio)
+static noinline void integrity_recheck(struct dm_integrity_io *dio, char *checksum)
 {
 	struct bio *bio = dm_bio_from_per_bio_data(dio, sizeof(struct dm_integrity_io));
 	struct dm_integrity_c *ic = dio->ic;
 	struct bvec_iter iter;
 	struct bio_vec bv;
 	sector_t sector, logical_sector, area, offset;
-	char checksum_onstack[max_t(size_t, HASH_MAX_DIGESTSIZE, MAX_TAG_SIZE)];
 	struct page *page;
 	void *buffer;
 
@@ -1735,8 +1734,8 @@ static void integrity_recheck(struct dm_
 			}
 
 			integrity_sector_checksum(ic, logical_sector, buffer,
-						  checksum_onstack);
-			r = dm_integrity_rw_tag(ic, checksum_onstack, &dio->metadata_block,
+						  checksum);
+			r = dm_integrity_rw_tag(ic, checksum, &dio->metadata_block,
 						&dio->metadata_offset, ic->tag_size, TAG_CMP);
 			if (r) {
 				if (r > 0) {
@@ -1851,7 +1850,7 @@ again:
 						checksums_ptr - checksums, dio->op == REQ_OP_READ ? TAG_CMP : TAG_WRITE);
 			if (unlikely(r)) {
 				if (r > 0) {
-					integrity_recheck(dio);
+					integrity_recheck(dio, checksums);
 					goto skip_io;
 				}
 				if (likely(checksums != checksums_onstack))
Index: linux-2.6/drivers/md/dm-verity-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-verity-target.c	2024-02-24 13:52:21.000000000 +0100
+++ linux-2.6/drivers/md/dm-verity-target.c	2024-02-24 13:55:42.000000000 +0100
@@ -491,8 +491,8 @@ static int verity_recheck_copy(struct dm
 	return 0;
 }
 
-static int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
-			  struct bvec_iter start, sector_t cur_block)
+static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
+				   struct bvec_iter start, sector_t cur_block)
 {
 	struct page *page;
 	void *buffer;