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

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
index cd76380af79fbbdd2a17cf356f8fd5cd72968290..7e6f51a9d91724378132219db30dd12789fd8a47 100644 (file)
--- 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;
 }
 
 /*