From 4d7b5a2cec6efb4dfd42a3fddf321d4d828e794d Mon Sep 17 00:00:00 2001
From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: Fri, 21 Jun 2024 13:35:03 +0200
Subject: [PATCH] mm: kfence: disable KMSAN when checking the canary

KMSAN warns about check_canary() accessing the canary.

The reason is that, even though set_canary() is properly instrumented and
sets shadow, slub explicitly poisons the canary's address range
afterwards.

Unpoisoning the canary is not the right thing to do: only check_canary()
is supposed to ever touch it.  Instead, disable KMSAN checks around canary
read accesses.

Link: https://lkml.kernel.org/r/20240621113706.315500-20-iii@linux.ibm.com
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Tested-by: Alexander Potapenko <glider@google.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/kfence/core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 964b8482275b..83f8e78827c0 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -305,8 +305,14 @@ metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state nex
 	WRITE_ONCE(meta->state, next);
 }
 
+#ifdef CONFIG_KMSAN
+#define check_canary_attributes noinline __no_kmsan_checks
+#else
+#define check_canary_attributes inline
+#endif
+
 /* Check canary byte at @addr. */
-static inline bool check_canary_byte(u8 *addr)
+static check_canary_attributes bool check_canary_byte(u8 *addr)
 {
 	struct kfence_metadata *meta;
 	unsigned long flags;
@@ -341,7 +347,8 @@ static inline void set_canary(const struct kfence_metadata *meta)
 		*((u64 *)addr) = KFENCE_CANARY_PATTERN_U64;
 }
 
-static inline void check_canary(const struct kfence_metadata *meta)
+static check_canary_attributes void
+check_canary(const struct kfence_metadata *meta)
 {
 	const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);
 	unsigned long addr = pageaddr;