linux-kernel - [PATCH 2/3] slub: Print raw pointer addresses when debugging

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Message-Id: <20210520013539.3733631-3-swboyd@chromium.org>
Date:   Wed, 19 May 2021 18:35:38 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org
Subject: [PATCH 2/3] slub: Print raw pointer addresses when debugging

Obscuring the pointers that slub shows when debugging makes for some
confusing slub debug messages:

 Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17

Those addresses are hashed for kernel security reasons. If we're trying
to be secure with slub_debug on the commandline we have some big
problems given that we dump whole chunks of kernel memory to the kernel
logs. Let's use %px here and dump buffers with the actual address for
the buffer instead of the hashed version so that the logs are
meaningful. This also helps if a kernel address is in some slub debug
report so we can figure out that the object is referencing itself.

Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 mm/slub.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index feda53ae62ba..87eeeed1f369 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -549,7 +549,7 @@ static void print_section(char *level, char *text, u8 *addr,
 			  unsigned int length)
 {
 	metadata_access_enable();
-	print_hex_dump(level, kasan_reset_tag(text), DUMP_PREFIX_ADDRESS,
+	print_hex_dump(level, kasan_reset_tag(text), DUMP_PREFIX_RAW_ADDRESS,
 			16, 1, addr, length, 1);
 	metadata_access_disable();
 }
@@ -650,7 +650,7 @@ void print_tracking(struct kmem_cache *s, void *object)
 
 static void print_page_info(struct page *page)
 {
-	pr_err("Slab 0x%p objects=%u used=%u fp=0x%p flags=%#lx(%pGp)\n",
+	pr_err("Slab 0x%px objects=%u used=%u fp=0x%px flags=%#lx(%pGp)\n",
 	       page, page->objects, page->inuse, page->freelist,
 	       page->flags, &page->flags);
 
@@ -707,7 +707,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 
 	print_page_info(page);
 
-	pr_err("Object 0x%p @offset=%tu fp=0x%p\n\n",
+	pr_err("Object 0x%px @offset=%tu fp=0x%px\n\n",
 	       p, p - addr, get_freepointer(s, p));
 
 	if (s->flags & SLAB_RED_ZONE)
@@ -777,7 +777,7 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
 static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
 						void *from, void *to)
 {
-	slab_fix(s, "Restoring 0x%p-0x%p=0x%x\n", from, to - 1, data);
+	slab_fix(s, "Restoring 0x%px-0x%px=0x%x\n", from, to - 1, data);
 	memset(from, data, to - from);
 }
 
@@ -800,7 +800,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
 		end--;
 
 	slab_bug(s, "%s overwritten", what);
-	pr_err("0x%p-0x%p @offset=%tu. First byte 0x%x instead of 0x%x\n",
+	pr_err("0x%px-0x%px @offset=%tu. First byte 0x%x instead of 0x%x\n",
 					fault, end - 1, fault - addr,
 					fault[0], value);
 	print_trailer(s, page, object);
@@ -893,7 +893,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 	while (end > fault && end[-1] == POISON_INUSE)
 		end--;
 
-	slab_err(s, page, "Padding overwritten. 0x%p-0x%p @offset=%tu",
+	slab_err(s, page, "Padding overwritten. 0x%px-0x%px @offset=%tu",
 			fault, end - 1, fault - start);
 	print_section(KERN_ERR, "Padding ", pad, remainder);
 
@@ -1041,7 +1041,7 @@ static void trace(struct kmem_cache *s, struct page *page, void *object,
 								int alloc)
 {
 	if (s->flags & SLAB_TRACE) {
-		pr_info("TRACE %s %s 0x%p inuse=%d fp=0x%p\n",
+		pr_info("TRACE %s %s 0x%px inuse=%d fp=0x%px\n",
 			s->name,
 			alloc ? "alloc" : "free",
 			object, page->inuse,
@@ -1186,7 +1186,7 @@ static inline int free_consistency_checks(struct kmem_cache *s,
 		struct page *page, void *object, unsigned long addr)
 {
 	if (!check_valid_pointer(s, page, object)) {
-		slab_err(s, page, "Invalid object pointer 0x%p", object);
+		slab_err(s, page, "Invalid object pointer 0x%px", object);
 		return 0;
 	}
 
@@ -1200,10 +1200,10 @@ static inline int free_consistency_checks(struct kmem_cache *s,
 
 	if (unlikely(s != page->slab_cache)) {
 		if (!PageSlab(page)) {
-			slab_err(s, page, "Attempt to free object(0x%p) outside of slab",
+			slab_err(s, page, "Attempt to free object(0x%px) outside of slab",
 				 object);
 		} else if (!page->slab_cache) {
-			pr_err("SLUB <none>: no slab for object 0x%p.\n",
+			pr_err("SLUB <none>: no slab for object 0x%px.\n",
 			       object);
 			dump_stack();
 		} else
@@ -1263,7 +1263,7 @@ static noinline int free_debug_processing(
 	slab_unlock(page);
 	spin_unlock_irqrestore(&n->list_lock, flags);
 	if (!ret)
-		slab_fix(s, "Object at 0x%p not freed", object);
+		slab_fix(s, "Object at 0x%px not freed", object);
 	return ret;
 }
 
@@ -3908,7 +3908,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 	for_each_object(p, s, addr, page->objects) {
 
 		if (!test_bit(__obj_to_index(s, addr, p), map)) {
-			pr_err("Object 0x%p @offset=%tu\n", p, p - addr);
+			pr_err("Object 0x%px @offset=%tu\n", p, p - addr);
 			print_tracking(s, p);
 		}
 	}
-- 
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