From: paulmck@kernel.org
To: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
kernel-team@fb.com, mingo@kernel.org
Cc: elver@google.com, andreyknvl@google.com, glider@google.com,
dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH kcsan 15/32] kcsan: Fix 0-sized checks
Date: Mon, 9 Mar 2020 12:04:03 -0700 [thread overview]
Message-ID: <20200309190420.6100-15-paulmck@kernel.org> (raw)
In-Reply-To: <20200309190359.GA5822@paulmck-ThinkPad-P72>
From: Marco Elver <elver@google.com>
Instrumentation of arbitrary memory-copy functions, such as user-copies,
may be called with size of 0, which could lead to false positives.
To avoid this, add a comparison in check_access() for size==0, which
will be optimized out for constant sized instrumentation
(__tsan_{read,write}N), and therefore not affect the common-case
fast-path.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/kcsan/core.c | 7 +++++++
kernel/kcsan/test.c | 10 ++++++++++
2 files changed, 17 insertions(+)
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index e3c7d8f..82c2bef 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -456,6 +456,13 @@ static __always_inline void check_access(const volatile void *ptr, size_t size,
long encoded_watchpoint;
/*
+ * Do nothing for 0 sized check; this comparison will be optimized out
+ * for constant sized instrumentation (__tsan_{read,write}N).
+ */
+ if (unlikely(size == 0))
+ return;
+
+ /*
* Avoid user_access_save in fast-path: find_watchpoint is safe without
* user_access_save, as the address that ptr points to is only used to
* check if a watchpoint exists; ptr is never dereferenced.
diff --git a/kernel/kcsan/test.c b/kernel/kcsan/test.c
index cc60002..d26a052 100644
--- a/kernel/kcsan/test.c
+++ b/kernel/kcsan/test.c
@@ -92,6 +92,16 @@ static bool test_matching_access(void)
return false;
if (WARN_ON(matching_access(9, 1, 10, 1)))
return false;
+
+ /*
+ * An access of size 0 could match another access, as demonstrated here.
+ * Rather than add more comparisons to 'matching_access()', which would
+ * end up in the fast-path for *all* checks, check_access() simply
+ * returns for all accesses of size 0.
+ */
+ if (WARN_ON(!matching_access(8, 8, 12, 0)))
+ return false;
+
return true;
}
--
2.9.5
next prev parent reply other threads:[~2020-03-09 19:05 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 19:03 [PATCH kcsan 0/32] KCSAN commits for v5.7 Paul E. McKenney
2020-03-09 19:03 ` [PATCH kcsan 01/32] kcsan: Prefer __always_inline for fast-path paulmck
2020-03-09 19:03 ` [PATCH kcsan 02/32] kcsan: Show full access type in report paulmck
2020-03-09 19:03 ` [PATCH kcsan 03/32] kcsan: Rate-limit reporting per data races paulmck
2020-03-09 19:03 ` [PATCH kcsan 04/32] kcsan: Make KCSAN compatible with lockdep paulmck
2020-03-09 19:03 ` [PATCH kcsan 05/32] kcsan: Address missing case with KCSAN_REPORT_VALUE_CHANGE_ONLY paulmck
2020-03-09 19:03 ` [PATCH kcsan 06/32] include/linux: Add instrumented.h infrastructure paulmck
2020-03-09 19:03 ` [PATCH kcsan 07/32] asm-generic, atomic-instrumented: Use generic instrumented.h paulmck
2020-03-09 19:03 ` [PATCH kcsan 08/32] asm-generic, kcsan: Add KCSAN instrumentation for bitops paulmck
2020-03-09 19:03 ` [PATCH kcsan 09/32] iov_iter: Use generic instrumented.h paulmck
2020-03-09 19:03 ` [PATCH kcsan 10/32] copy_to_user, copy_from_user: " paulmck
2020-03-09 19:03 ` [PATCH kcsan 11/32] kcsan: Add docbook header for data_race() paulmck
2020-03-09 19:04 ` [PATCH kcsan 12/32] kcsan: Add option to assume plain aligned writes up to word size are atomic paulmck
2020-03-09 19:04 ` [PATCH kcsan 13/32] kcsan: Clarify Kconfig option KCSAN_IGNORE_ATOMICS paulmck
2020-03-09 19:04 ` [PATCH kcsan 14/32] kcsan: Cleanup of main KCSAN Kconfig option paulmck
2020-03-09 19:04 ` paulmck [this message]
2020-03-09 19:04 ` [PATCH kcsan 16/32] kcsan: Introduce KCSAN_ACCESS_ASSERT access type paulmck
2020-03-09 19:04 ` [PATCH kcsan 17/32] kcsan: Introduce ASSERT_EXCLUSIVE_* macros paulmck
2020-03-13 8:52 ` Boqun Feng
2020-03-13 16:15 ` Marco Elver
2020-03-14 2:22 ` Boqun Feng
2020-03-17 11:12 ` Marco Elver
2020-03-19 3:23 ` Boqun Feng
2020-03-20 14:49 ` Marco Elver
2020-03-09 19:04 ` [PATCH kcsan 18/32] kcsan: Add test to generate conflicts via debugfs paulmck
2020-03-09 19:04 ` [PATCH kcsan 19/32] kcsan: Expose core configuration parameters as module params paulmck
2020-03-09 19:04 ` [PATCH kcsan 20/32] kcsan: Fix misreporting if concurrent races on same address paulmck
2020-03-09 19:04 ` [PATCH kcsan 21/32] kcsan: Move interfaces that affects checks to kcsan-checks.h paulmck
2020-03-09 19:04 ` [PATCH kcsan 22/32] compiler.h, seqlock.h: Remove unnecessary kcsan.h includes paulmck
2020-03-09 19:04 ` [PATCH kcsan 23/32] kcsan: Introduce kcsan_value_change type paulmck
2020-03-09 19:04 ` [PATCH kcsan 24/32] kcsan: Add kcsan_set_access_mask() support paulmck
2020-03-09 19:04 ` [PATCH kcsan 25/32] kcsan: Introduce ASSERT_EXCLUSIVE_BITS(var, mask) paulmck
2020-03-09 19:04 ` [PATCH kcsan 26/32] kcsan, trace: Make KCSAN compatible with tracing paulmck
2020-03-09 19:57 ` Steven Rostedt
2020-03-09 20:27 ` Paul E. McKenney
2020-03-09 19:04 ` [PATCH kcsan 27/32] kcsan: Add option to allow watcher interruptions paulmck
2020-03-12 18:03 ` Paul E. McKenney
2020-03-12 18:04 ` Paul E. McKenney
2020-03-13 15:28 ` Marco Elver
2020-03-16 13:56 ` Marco Elver
2020-03-16 15:45 ` Paul E. McKenney
2020-03-16 16:22 ` Marco Elver
2020-03-17 17:13 ` Paul E. McKenney
2020-03-17 17:44 ` Marco Elver
2020-03-18 17:42 ` Marco Elver
2020-03-09 19:04 ` [PATCH kcsan 28/32] kcsan: Add option for verbose reporting paulmck
2020-03-09 19:04 ` [PATCH kcsan 29/32] kcsan: Add current->state to implicitly atomic accesses paulmck
2020-03-09 19:04 ` [PATCH kcsan 30/32] kcsan: Fix a typo in a comment paulmck
2020-03-09 19:04 ` [PATCH kcsan 31/32] kcsan: Update Documentation/dev-tools/kcsan.rst paulmck
2020-03-09 19:04 ` [PATCH kcsan 32/32] kcsan: Update API documentation in kcsan-checks.h paulmck
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