+ kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch added to -mm tree

* + kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch added to -mm tree
@ 2021-04-06  1:46 akpm
  2021-04-15 18:17 ` Peter Collingbourne
  0 siblings, 1 reply; 3+ messages in thread
From: akpm @ 2021-04-06  1:46 UTC (permalink / raw)
  To: andreyknvl, dvyukov, elver, eugenis, glider, mm-commits, pcc


The patch titled
     Subject: kasan: fix kasan_byte_accessible() to be consistent with actual checks
has been added to the -mm tree.  Its filename is
     kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Peter Collingbourne <pcc@google.com>
Subject: kasan: fix kasan_byte_accessible() to be consistent with actual checks

We can sometimes end up with kasan_byte_accessible() being called on
non-slab memory.  For example ksize() and krealloc() may end up calling it
on KFENCE allocated memory.  In this case the memory will be tagged with
KASAN_SHADOW_INIT, which a subsequent patch ("kasan: initialize shadow to
TAG_INVALID for SW_TAGS") will set to the same value as KASAN_TAG_INVALID,
causing kasan_byte_accessible() to fail when called on non-slab memory.

This highlighted the fact that the check in kasan_byte_accessible() was
inconsistent with checks as implemented for loads and stores
(kasan_check_range() in SW tags mode and hardware-implemented checks in HW
tags mode).  kasan_check_range() does not have a check for
KASAN_TAG_INVALID, and instead has a comparison against
KASAN_SHADOW_START.  In HW tags mode, we do not have either, but we do set
TCR_EL1.TCMA which corresponds with the comparison against
KASAN_TAG_KERNEL.

Therefore, update kasan_byte_accessible() for both SW and HW tags modes to
correspond with the respective checks on loads and stores.

Link: https://linux-review.googlesource.com/id/Ic6d40803c57dcc6331bd97fbb9a60b0d38a65a36
Link: https://lkml.kernel.org/r/20210405220647.1965262-1-pcc@google.com
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kasan/kasan.h   |    3 +--
 mm/kasan/sw_tags.c |   10 +++++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

--- a/mm/kasan/kasan.h~kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks
+++ a/mm/kasan/kasan.h
@@ -369,8 +369,7 @@ static inline bool kasan_byte_accessible
 	u8 ptr_tag = get_tag(addr);
 	u8 mem_tag = hw_get_mem_tag((void *)addr);
 
-	return (mem_tag != KASAN_TAG_INVALID) &&
-		(ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag);
+	return ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag;
 }
 
 #else /* CONFIG_KASAN_HW_TAGS */
--- a/mm/kasan/sw_tags.c~kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks
+++ a/mm/kasan/sw_tags.c
@@ -121,10 +121,14 @@ bool kasan_check_range(unsigned long add
 bool kasan_byte_accessible(const void *addr)
 {
 	u8 tag = get_tag(addr);
-	u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(kasan_reset_tag(addr)));
+	void *untagged_addr = kasan_reset_tag(addr);
+	u8 shadow_byte;
 
-	return (shadow_byte != KASAN_TAG_INVALID) &&
-		(tag == KASAN_TAG_KERNEL || tag == shadow_byte);
+	if (untagged_addr < kasan_shadow_to_mem((void *)KASAN_SHADOW_START))
+		return false;
+
+	shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr));
+	return tag == KASAN_TAG_KERNEL || tag == shadow_byte;
 }
 
 #define DEFINE_HWASAN_LOAD_STORE(size)					\
_

Patches currently in -mm which might be from pcc@google.com are

kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks.patch


^ permalink raw reply	[flat|nested] 3+ messages in thread