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| author |   Marco Elver <elver@google.com> | 2020-02-05 11:14:19 +0100 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2020-03-21 09:42:42 +0100 |
| commit | ed95f95c86cd53621103d865d62b5e1f96e60edb (patch) | |
| tree | 494951a23a0a3a22bccecb1de3ae460ee31cc1c0 /kernel/kcsan | |
| parent | kcsan: Clean up the main KCSAN Kconfig option (diff) | |
| download | linux-dev-ed95f95c86cd53621103d865d62b5e1f96e60edb.tar.xz linux-dev-ed95f95c86cd53621103d865d62b5e1f96e60edb.zip | |
kcsan: Fix 0-sized checks
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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/kcsan')
| -rw-r--r-- | kernel/kcsan/core.c | 7 | ||||
| -rw-r--r-- | kernel/kcsan/test.c | 10 |
2 files changed, 17 insertions, 0 deletions
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index e3c7d8f34f2f..82c2bef827d4 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 cc6000239dc0..d26a052d3383 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; } |