Messages in this thread Patch in this message | | | From | Borislav Petkov <> | Subject | [PATCH] x86/mce: Do not overwrite MCi_STATUS in mce_no_way_out() | Date | Thu, 21 Jun 2018 14:40:00 +0200 |
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From: Borislav Petkov <bp@suse.de>
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}
Change it to use a temporary variable and save to mce.status only when valid. It will still overwrite the old status value if more than one MCEs are logged, which warrants the second change in this patch:
Return immediately when severity is a panic one so that we can panic immediately with the first fatal MCE logged.
Cc: <stable@vger.kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> --- arch/x86/kernel/cpu/mcheck/mce.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 5c38d1f861f2..5c0a97b2bfce 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -772,12 +772,15 @@ EXPORT_SYMBOL_GPL(machine_check_poll); static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp, struct pt_regs *regs) { + u64 mci_status; int i, ret = 0; char *tmp; for (i = 0; i < mca_cfg.banks; i++) { - m->status = mce_rdmsrl(msr_ops.status(i)); - if (m->status & MCI_STATUS_VAL) { + mci_status = mce_rdmsrl(msr_ops.status(i)); + if (mci_status & MCI_STATUS_VAL) { + m->status = mci_status; + __set_bit(i, validp); if (quirk_no_way_out) quirk_no_way_out(i, m, regs); @@ -785,7 +788,7 @@ static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp, if (mce_severity(m, mca_cfg.tolerant, &tmp, true) >= MCE_PANIC_SEVERITY) { *msg = tmp; - ret = 1; + return 1; } } return ret; -- 2.17.0.582.gccdcbd54c
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