x86/mce: Fix use of uninitialized MCE message string

mainline inclusion
from mainline-v5.6-rc1
commit 7a8bc2b0
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4MKP4


CVE: NA

--------------------------------

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


Signed-off-by: Jackie Liu <liuyun01@kylinos.cn> #openEuler_contributor
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>

arch/x86/kernel/cpu/mce/core.c

@@ -793,7 +793,7 @@ 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 < mca_cfg.banks; i++) {
@@ -1218,8 +1218,8 @@ 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;
 
 	/*