x86/mce: Fix use of uninitialized MCE message string

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. Schönherr <jschoenh@amazon.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200103150722.20313-4-jschoenh@amazon.de

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 81b97a6..bfb20c2 100644 (file)
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -795,7 +795,7 @@ 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++) {
@@ -1220,8 +1220,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
        DECLARE_BITMAP(toclear, MAX_NR_BANKS);
        struct mca_config *cfg = &mca_cfg;
        int cpu = smp_processor_id();
-       char *msg = "Unknown";
        struct mce m, *final;
+       char *msg = NULL;
        int worst = 0;
 
        /*