mm/slub: clarify verification reporting

Patch series "Actually fix freelist pointer vs redzoning", v4.

This fixes redzoning vs the freelist pointer (both for middle-position
and very small caches).  Both are "theoretical" fixes, in that I see no
evidence of such small-sized caches actually be used in the kernel, but
that's no reason to let the bugs continue to exist, especially since
people doing local development keep tripping over it.  :)

This patch (of 3):

Instead of repeating "Redzone" and "Poison", clarify which sides of
those zones got tripped.  Additionally fix column alignment in the
trailer.

Before:

  BUG test (Tainted: G    B            ): Redzone overwritten
  ...
  Redzone (____ptrval____): bb bb bb bb bb bb bb bb      ........
  Object (____ptrval____): f6 f4 a5 40 1d e8            ...@..
  Redzone (____ptrval____): 1a aa                        ..
  Padding (____ptrval____): 00 00 00 00 00 00 00 00      ........

After:

  BUG test (Tainted: G    B            ): Right Redzone overwritten
  ...
  Redzone  (____ptrval____): bb bb bb bb bb bb bb bb      ........
  Object   (____ptrval____): f6 f4 a5 40 1d e8            ...@..
  Redzone  (____ptrval____): 1a aa                        ..
  Padding  (____ptrval____): 00 00 00 00 00 00 00 00      ........

The earlier commits that slowly resulted in the "Before" reporting were:

  d86bd1bece6f ("mm/slub: support left redzone")
  ffc79d288000 ("slub: use print_hex_dump")
  2492268472e7 ("SLUB: change error reporting format to follow lockdep loosely")

Link: https://lkml.kernel.org/r/20210608183955.280836-1-keescook@chromium.org
Link: https://lkml.kernel.org/r/20210608183955.280836-2-keescook@chromium.org
Link: https://lore.kernel.org/lkml/cfdb11d7-fb8e-e578-c939-f7f5fb69a6bd@suse.cz/
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Marco Elver <elver@google.com>
Cc: "Lin, Zhenpeng" <zplin@psu.edu>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 03f294a..d302855 100644 (file)
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -181,7 +181,7 @@ SLUB Debug output
 Here is a sample of slub debug output::
 
  ====================================================================
- BUG kmalloc-8: Redzone overwritten
+ BUG kmalloc-8: Right Redzone overwritten
  --------------------------------------------------------------------
 
  INFO: 0xc90f6d28-0xc90f6d2b. First byte 0x00 instead of 0xcc
@@ -189,10 +189,10 @@ Here is a sample of slub debug output::
  INFO: Object 0xc90f6d20 @offset=3360 fp=0xc90f6d58
  INFO: Allocated in get_modalias+0x61/0xf5 age=53 cpu=1 pid=554
 
- Bytes b4 0xc90f6d10:  00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
-   Object 0xc90f6d20:  31 30 31 39 2e 30 30 35                         1019.005
-  Redzone 0xc90f6d28:  00 cc cc cc                                     .
-  Padding 0xc90f6d50:  5a 5a 5a 5a 5a 5a 5a 5a                         ZZZZZZZZ
+ Bytes b4 (0xc90f6d10): 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
+ Object   (0xc90f6d20): 31 30 31 39 2e 30 30 35                         1019.005
+ Redzone  (0xc90f6d28): 00 cc cc cc                                     .
+ Padding  (0xc90f6d50): 5a 5a 5a 5a 5a 5a 5a 5a                         ZZZZZZZZ
 
    [<c010523d>] dump_trace+0x63/0x1eb
    [<c01053df>] show_trace_log_lvl+0x1a/0x2f

diff --git a/mm/slub.c b/mm/slub.c
index 3f96e09..f91d9fe 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -712,15 +712,15 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
               p, p - addr, get_freepointer(s, p));
 
        if (s->flags & SLAB_RED_ZONE)
-               print_section(KERN_ERR, "Redzone ", p - s->red_left_pad,
+               print_section(KERN_ERR, "Redzone  ", p - s->red_left_pad,
                              s->red_left_pad);
        else if (p > addr + 16)
                print_section(KERN_ERR, "Bytes b4 ", p - 16, 16);
 
-       print_section(KERN_ERR, "Object ", p,
+       print_section(KERN_ERR,         "Object   ", p,
                      min_t(unsigned int, s->object_size, PAGE_SIZE));
        if (s->flags & SLAB_RED_ZONE)
-               print_section(KERN_ERR, "Redzone ", p + s->object_size,
+               print_section(KERN_ERR, "Redzone  ", p + s->object_size,
                        s->inuse - s->object_size);
 
        off = get_info_end(s);
@@ -732,7 +732,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 
        if (off != size_from_object(s))
                /* Beginning of the filler is the free pointer */
-               print_section(KERN_ERR, "Padding ", p + off,
+               print_section(KERN_ERR, "Padding  ", p + off,
                              size_from_object(s) - off);
 
        dump_stack();
@@ -909,11 +909,11 @@ static int check_object(struct kmem_cache *s, struct page *page,
        u8 *endobject = object + s->object_size;
 
        if (s->flags & SLAB_RED_ZONE) {
-               if (!check_bytes_and_report(s, page, object, "Redzone",
+               if (!check_bytes_and_report(s, page, object, "Left Redzone",
                        object - s->red_left_pad, val, s->red_left_pad))
                        return 0;
 
-               if (!check_bytes_and_report(s, page, object, "Redzone",
+               if (!check_bytes_and_report(s, page, object, "Right Redzone",
                        endobject, val, s->inuse - s->object_size))
                        return 0;
        } else {
@@ -928,7 +928,7 @@ static int check_object(struct kmem_cache *s, struct page *page,
                if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) &&
                        (!check_bytes_and_report(s, page, p, "Poison", p,
                                        POISON_FREE, s->object_size - 1) ||
-                        !check_bytes_and_report(s, page, p, "Poison",
+                        !check_bytes_and_report(s, page, p, "End Poison",
                                p + s->object_size - 1, POISON_END, 1)))
                        return 0;
                /*