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Date:   Fri, 20 Dec 2019 11:01:06 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Jan =?utf-8?Q?H=2E_Sch=C3=B6nherr?= <jschoenh@amazon.de>
Cc:     Tony Luck <tony.luck@intel.com>, linux-edac@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
Subject: Re: [PATCH 4/6] x86/mce: Fix handling of optional message string
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On Thu, Dec 19, 2019 at 06:49:32PM +0100, Jan H. Schönherr wrote:
> Not quite. mce_panic() already handles NULL as a value for "exp" (not "msg").
> 
> We still need to pass NULL or a proper pointer. Not some uninitialized, potentially
> random data.
> 
> So, at the very least we need to initialize "tmp" in mce_no_way_out(), if you're looking
> for a minimal patch.

Yes, sure, this is what I'm thinking of.

And yes, I'm not going to cry if we don't print the immensely helpful
"Unknown" anymore.</sarcasm>

---
diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 68dd4b358740..fd23f9f53379 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -798,7 +798,7 @@ 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 = NULL;
 	int i;
 
 	for (i = 0; i < this_cpu_read(mce_num_banks); i++) {
@@ -1223,8 +1223,8 @@ 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;
 
 	/*

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette