linux-kernel - Re: [PATCH 1/2] x86, microcode: Sanitize per-cpu microcode reloading interface

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Date:	Wed, 20 Jun 2012 01:38:11 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	X86-ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/2] x86, microcode: Sanitize per-cpu microcode reloading
 interface

On Tue, Jun 19, 2012 at 11:15:56PM +0000, Yu, Fenghua wrote:
> > diff --git a/arch/x86/kernel/microcode_core.c
> > b/arch/x86/kernel/microcode_core.c
> > index fbdfc6917180..24b852b61be3 100644
> > --- a/arch/x86/kernel/microcode_core.c
> > +++ b/arch/x86/kernel/microcode_core.c
> > @@ -298,19 +298,31 @@ static ssize_t reload_store(struct device *dev,
> >  			    const char *buf, size_t size)
> >  {
> >  	unsigned long val;
> > -	int cpu = dev->id;
> > -	ssize_t ret = 0;
> > +	int cpu;
> > +	ssize_t ret = 0, tmp_ret;
> > +
> > +	/* allow reload only from the BSP */
> > +	if (boot_cpu_data.cpu_index != dev->id)
> > +		return -EINVAL;
> 
> With the /sys/devices/system/cpu/microcode/reload interface in your
> patch 2/2, this will be broken, right?

Actually it works per chance and passed testing. And I think I know why:
now the reload sysfs node is not per-cpu, this dev->id is always 0 and
thus the check passes.

> With the new interface, reload_store() can be executed on any cpu or
> dev. I think you need to remove this check if working with the patch
> 2/2.

But you're right, will fix.

Thanks for the review.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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