On 9/18/2018 11:41 AM, Jiri Slaby wrote:
On 09/17/2018, 11:33 PM, Matthias Kaehlcke wrote:
sysrq_handle_crash() dereferences a NULL pointer on purpose to force
an exception, the local variable 'killer' is assigned to NULL and
dereferenced later. Clang detects the NULL pointer dereference at compile
time and emits a BRK instruction (on arm64) instead of the expected NULL
pointer exception. Change 'killer' to a global variable (and rename it
to 'sysrq_killer' to avoid possible clashes) to prevent Clang from
detecting the condition. By default global variables are initialized
with zero/NULL in C, therefore an explicit initialization is not needed.
Reported-by: Sai Prakash Ranjan <saiprakash.ran...@codeaurora.org>
Suggested-by: Evan Green <evgr...@chromium.org>
Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
---
drivers/tty/sysrq.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 06ed20dd01ba..49fa8e758690 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -132,10 +132,10 @@ static struct sysrq_key_op sysrq_unraw_op = {
#define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
#endif /* CONFIG_VT */
+char *sysrq_killer;
+
static void sysrq_handle_crash(int key)
{
- char *killer = NULL;
-
/* we need to release the RCU read lock here,
* otherwise we get an annoying
* 'BUG: sleeping function called from invalid context'
@@ -144,7 +144,7 @@ static void sysrq_handle_crash(int key)
rcu_read_unlock();
panic_on_oops = 1; /* force panic */
wmb();
- *killer = 1;
+ *sysrq_killer = 1;
Just because a static analyzer is wrong? Oh wait, even compiler is
wrong. At least make it a static global. Or what about OPTIMIZER_HIDE_VAR?
static global does not work, clang still inserts brk. As for
OPTIMIZE_HIDE_VAR, it seems to work.
But, I dont think it is defined for clang in which case it defaults to
using barrier(). There is already one wmb(), so will it be right?
--
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