The following commit has been merged into the locking/kcsan branch of tip:
Commit-ID: ed95f95c86cd53621103d865d62b5e1f96e60edb
Gitweb: https://git.kernel.org/tip/ed95f95c86cd53621103d865d62b5e1f96e60edb
Author: Marco Elver <elver@xxxxxxxxxx>
AuthorDate: Wed, 05 Feb 2020 11:14:19 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sat, 21 Mar 2020 09:42:42 +01:00
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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
}
|