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

commit 1f74c8a64798e2c488f86efc97e308b85fb7d7aa upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 886a44a1ecea55f6c8d9e7c8218ef16af02a6f9f..c49e146d433294f2efa49d7022b2f3b67129954c 100644 (file)
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -738,23 +738,25 @@ 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;
 }
 
 /*