x86/mce: Do not overwrite MCi_STATUS in mce_no_way_out()

suryasaimadhu · KAGA-KOKO · commit 1f74c8a64798 · 2018-06-22T14:35:50.000+02:00
mce_no_way_out() does a quick check during #MC to see whether some of the MCEs logged would require the kernel to panic immediately. And it passes a struct mce where MCi_STATUS gets written. However, after having saved a valid status value, the next iteration of the loop which goes over the MCA banks on the CPU, overwrites the valid status value because we're using struct mce as storage instead of a temporary variable. Which leads to MCE records with an empty status value: mce: [Hardware Error]: CPU 0: Machine Check Exception: 6 Bank 0: 0000000000000000 mce: [Hardware Error]: RIP 10:<ffffffffbd42fbd7> {trigger_mce+0x7/0x10} In order to prevent the loss of the status register value, return immediately when severity is a panic one so that we can panic immediately with the first fatal MCE logged. This is also the intention of this function and not to noodle over the banks while a fatal MCE is already logged. Tony: read the rest of the MCA bank to populate the struct mce fully. Suggested-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: <stable@vger.kernel.org> Link: https://lkml.kernel.org/r/20180622095428.626-8-bp@alien8.de
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -772,23 +772,25 @@ EXPORT_SYMBOL_GPL(machine_check_poll);
 static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp,
 			  struct pt_regs *regs)
 {
-	int i, ret = 0;
 	char *tmp;
+	int i;
 
 	for (i = 0; i < mca_cfg.banks; i++) {
 		m->status = mce_rdmsrl(msr_ops.status(i));
-		if (m->status & MCI_STATUS_VAL) {
-			__set_bit(i, validp);
-			if (quirk_no_way_out)
-				quirk_no_way_out(i, m, regs);
-		}
+		if (!(m->status & MCI_STATUS_VAL))
+			continue;
+
+		__set_bit(i, validp);
+		if (quirk_no_way_out)
+			quirk_no_way_out(i, m, regs);
 
 		if (mce_severity(m, mca_cfg.tolerant, &tmp, true) >= MCE_PANIC_SEVERITY) {
+			mce_read_aux(m, i);
 			*msg = tmp;
-			ret = 1;
+			return 1;
 		}
 	}
-	return ret;
+	return 0;
 }
 
 /*
