[PATCH v2 3/6] x86/mce: Fix use of uninitialized MCE message string

From: Jan H. SchÃnherr
Date: Fri Jan 03 2020 - 10:07:45 EST

The function mce_severity() is not required to update its msg argument.
In fact, mce_severity_amd() does not, which makes mce_no_way_out()
return uninitialized data, which may be used later for printing.

Assuming that implementations of mce_severity() either always or never
update the msg argument (which is currently the case), it is sufficient
to initialize the temporary variable in mce_no_way_out().

While at it, avoid printing a useless "Unknown".

Signed-off-by: Jan H. SchÃnherr <jschoenh@xxxxxxxxx>
Changes v1->v2:
- simplify fix by assuming that mce_severity() either always or never
updates the msg argument -- as opposed to mce_severity() having the
freedom to decide on a case by case basis (requested by Boris);
- stop printing "Unknown" (requested by Boris).
arch/x86/kernel/cpu/mce/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 0ccd6cf3402d..1d91ce956772 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -790,7 +790,7 @@ EXPORT_SYMBOL_GPL(machine_check_poll);
static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp,
struct pt_regs *regs)
- char *tmp;
+ char *tmp = *msg;
int i;

for (i = 0; i < this_cpu_read(mce_num_banks); i++) {
@@ -1209,8 +1209,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
struct mca_config *cfg = &mca_cfg;
int cpu = smp_processor_id();
- char *msg = "Unknown";
struct mce m, *final;
+ char *msg = NULL;
int worst = 0;