Re: [Crash-utility] [PATCH] kmem -s/-S not working properly on RHEL8.6/8.7
Yet another round (sorry) with simpler freelist_ptr_bswap_x86() using "disassemble
__slab_free".
Signed-off-by: Georges Aureau <georges.aureau(a)hpe.com>
----
defs.h | 1 +
memory.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/defs.h b/defs.h
index 33a823b..56d6cf4 100644
--- a/defs.h
+++ b/defs.h
@@ -2638,6 +2638,7 @@ struct vm_table { /* kernel VM-related data */
#define SLAB_OVERLOAD_PAGE (0x8000000)
#define SLAB_CPU_CACHE (0x10000000)
#define SLAB_ROOT_CACHES (0x20000000)
+#define FREELIST_PTR_BSWAP (0x40000000)
#define IS_FLATMEM() (vt->flags & FLATMEM)
#define IS_DISCONTIGMEM() (vt->flags & DISCONTIGMEM)
diff --git a/memory.c b/memory.c
index 5141fbe..edd6cd8 100644
--- a/memory.c
+++ b/memory.c
@@ -320,6 +320,7 @@ static void dump_per_cpu_offsets(void);
static void dump_page_flags(ulonglong);
static ulong kmem_cache_nodelists(ulong);
static void dump_hstates(void);
+static void freelist_ptr_init(void);
static ulong freelist_ptr(struct meminfo *, ulong, ulong);
static ulong handle_each_vm_area(struct handle_each_vm_area_args *);
@@ -789,6 +790,8 @@ vm_init(void)
MEMBER_OFFSET_INIT(kmem_cache_name, "kmem_cache",
"name");
MEMBER_OFFSET_INIT(kmem_cache_flags, "kmem_cache",
"flags");
MEMBER_OFFSET_INIT(kmem_cache_random, "kmem_cache",
"random");
+ if (VALID_MEMBER(kmem_cache_random))
+ freelist_ptr_init();
MEMBER_OFFSET_INIT(kmem_cache_cpu_freelist, "kmem_cache_cpu",
"freelist");
MEMBER_OFFSET_INIT(kmem_cache_cpu_page, "kmem_cache_cpu",
"page");
if (INVALID_MEMBER(kmem_cache_cpu_page))
@@ -13932,6 +13935,8 @@ dump_vm_table(int verbose)
fprintf(fp, "%sSLAB_CPU_CACHE", others++ ? "|" :
"");\
if (vt->flags & SLAB_ROOT_CACHES)
fprintf(fp, "%sSLAB_ROOT_CACHES", others++ ? "|" :
"");\
+ if (vt->flags & FREELIST_PTR_BSWAP)
+ fprintf(fp, "%sFREELIST_PTR_BSWAP", others++ ? "|" :
"");\
if (vt->flags & USE_VMAP_AREA)
fprintf(fp, "%sUSE_VMAP_AREA", others++ ? "|" :
"");\
if (vt->flags & CONFIG_NUMA)
@@ -19519,13 +19524,51 @@ count_free_objects(struct meminfo *si, ulong freelist)
return c;
}
+/*
+ * With CONFIG_SLAB_FREELIST_HARDENED, freelist_ptr's are crypted with xor's,
+ * and for recent release with an additionnal bswap. Some releases prio to 5.7.0
+ * may be using the additionnal bswap. The only easy and reliable way to tell is
+ * to inspect assembly code (eg. "__slab_free") for a bswap instruction.
+ */
+static int
+freelist_ptr_bswap_x86(void)
+{
+ char buf1[BUFSIZE];
+ char buf2[BUFSIZE];
+ char *arglist[MAXARGS];
+ int found;
+ sprintf(buf1, "disassemble __slab_free");
+ open_tmpfile();
+ gdb_pass_through(buf1, pc->tmpfile, GNU_RETURN_ON_ERROR);
+ rewind(pc->tmpfile);
+ found = FALSE;
+ while (fgets(buf2, BUFSIZE, pc->tmpfile)) {
+ if (parse_line(buf2, arglist) < 3)
+ continue;
+ if (STREQ(arglist[2], "bswap")) {
+ found = TRUE;
+ break;
+ }
+ }
+ close_tmpfile();
+ return found;
+}
+
+static void
+freelist_ptr_init(void)
+{
+ if (THIS_KERNEL_VERSION >= LINUX(5,7,0) ||
+ ((machine_type("X86_64") || machine_type("X86"))
&& freelist_ptr_bswap_x86()))
+ vt->flags |= FREELIST_PTR_BSWAP;
+}
+
static ulong
freelist_ptr(struct meminfo *si, ulong ptr, ulong ptr_addr)
{
if (VALID_MEMBER(kmem_cache_random)) {
/* CONFIG_SLAB_FREELIST_HARDENED */
- if (THIS_KERNEL_VERSION >= LINUX(5,7,0))
+ if (vt->flags & FREELIST_PTR_BSWAP)
ptr_addr = (sizeof(long) == 8) ? bswap_64(ptr_addr)
: bswap_32(ptr_addr);
return (ptr ^ si->random ^ ptr_addr);