[Crash-utility] [PATCH] Fix the "kmem -s" option for Linux 5.7 and later kernels

[Lianbo Jiang]

Linux 5.7 and later kernels that contain kernel commit <1ad53d9fa3f6>
("slub: improve bit diffusion for freelist ptr obfuscation") changed
the calculation formula in the freelist_ptr(), which added a swab()
call to mix bits a little more. When kernel is built with the
"CONFIG_SLAB_FREELIST_HARDENED=y",the "kmem -s" option fails with the
following errors, if there is no such patch.

crash> kmem -s
CACHE             OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE  NAME
82166d00              144          0         0      0     4k  fuse_request
82166e00              792          0         0      0    16k  fuse_inode
87201e00              528          0         0      0     8k  xfs_dqtrx
87201f00              496          0         0      0     8k  xfs_dquot
kmem: xfs_buf: slab: 37202e6e900 invalid freepointer: b844bab900001d70
kmem: xfs_buf: slab: 3720250fd80 invalid freepointer: b8603f9400001370
...

Signed-off-by: Lianbo Jiang <lijiang at redhat.com>
---
 memory.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/memory.c b/memory.c
index 8c6bbe409922..a3cf8a86728d 100644
--- a/memory.c
+++ b/memory.c
@@ -20,6 +20,7 @@
 #include <sys/mman.h>
 #include <ctype.h>
 #include <netinet/in.h>
+#include <byteswap.h>
 
 struct meminfo {           /* general purpose memory information structure */
         ulong cache;       /* used by the various memory searching/dumping */
@@ -19336,10 +19337,14 @@ count_free_objects(struct meminfo *si, ulong freelist)
 static ulong
 freelist_ptr(struct meminfo *si, ulong ptr, ulong ptr_addr)
 {
-	if (VALID_MEMBER(kmem_cache_random))
+	if (VALID_MEMBER(kmem_cache_random)) {
 		/* CONFIG_SLAB_FREELIST_HARDENED */
+
+		if (THIS_KERNEL_VERSION >= LINUX(5,7,0))
+			ptr_addr = (sizeof(long) == 8) ? bswap_64(ptr_addr)
+						       : bswap_32(ptr_addr);
 		return (ptr ^ si->random ^ ptr_addr);
-	else
+	} else
 		return ptr;
 }
 
-- 
2.17.1