Date:   Tue, 18 Aug 2020 15:40:43 -0700
From:   akpm@linux-foundation.org
To:     cai@lca.pw, catalin.marinas@arm.com, elver@google.com,
        mm-commits@vger.kernel.org
Subject:  [merged]
 mm-kmemleak-silence-kcsan-splats-in-checksum.patch removed from -mm tree
Message-ID: <20200818224043.gkzKcDILS%akpm@linux-foundation.org>
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Sender: mm-commits-owner@vger.kernel.org
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Reply-To: linux-kernel@vger.kernel.org


The patch titled
     Subject: mm/kmemleak: silence KCSAN splats in checksum
has been removed from the -mm tree.  Its filename was
     mm-kmemleak-silence-kcsan-splats-in-checksum.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Qian Cai <cai@lca.pw>
Subject: mm/kmemleak: silence KCSAN splats in checksum

Even if KCSAN is disabled for kmemleak, update_checksum() could still call
crc32() (which is outside of kmemleak.c) to dereference object->pointer. 
Thus, the value of object->pointer could be accessed concurrently as
noticed by KCSAN,

 BUG: KCSAN: data-race in crc32_le_base / do_raw_spin_lock

 write to 0xffffb0ea683a7d50 of 4 bytes by task 23575 on cpu 12:
  do_raw_spin_lock+0x114/0x200
  debug_spin_lock_after at kernel/locking/spinlock_debug.c:91
  (inlined by) do_raw_spin_lock at kernel/locking/spinlock_debug.c:115
  _raw_spin_lock+0x40/0x50
  __handle_mm_fault+0xa9e/0xd00
  handle_mm_fault+0xfc/0x2f0
  do_page_fault+0x263/0x6f9
  page_fault+0x34/0x40

 read to 0xffffb0ea683a7d50 of 4 bytes by task 839 on cpu 60:
  crc32_le_base+0x67/0x350
  crc32_le_base+0x67/0x350:
  crc32_body at lib/crc32.c:106
  (inlined by) crc32_le_generic at lib/crc32.c:179
  (inlined by) crc32_le at lib/crc32.c:197
  kmemleak_scan+0x528/0xd90
  update_checksum at mm/kmemleak.c:1172
  (inlined by) kmemleak_scan at mm/kmemleak.c:1497
  kmemleak_scan_thread+0xcc/0xfa
  kthread+0x1e0/0x200
  ret_from_fork+0x27/0x50

If a shattered value was returned due to a data race, it will be corrected
in the next scan.  Thus, let KCSAN ignore all reads in the region to
silence KCSAN in case the write side is non-atomic.

Link: http://lkml.kernel.org/r/20200317182754.2180-1-cai@lca.pw
Signed-off-by: Qian Cai <cai@lca.pw>
Suggested-by: Marco Elver <elver@google.com>
Acked-by: Marco Elver <elver@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kmemleak.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/kmemleak.c~mm-kmemleak-silence-kcsan-splats-in-checksum
+++ a/mm/kmemleak.c
@@ -1169,8 +1169,10 @@ static bool update_checksum(struct kmeml
 	u32 old_csum = object->checksum;
 
 	kasan_disable_current();
+	kcsan_disable_current();
 	object->checksum = crc32(0, (void *)object->pointer, object->size);
 	kasan_enable_current();
+	kcsan_enable_current();
 
 	return object->checksum != old_csum;
 }
_

Patches currently in -mm which might be from cai@lca.pw are

fork-silence-a-false-postive-warning-in-__mmdrop.patch