linux-kernel - Re: [PATCH 8/8] x86, microcode, intel: defend apply_microcode_intel with BUG

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Date:	Fri, 7 Nov 2014 20:56:39 -0200
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org, H Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH 8/8] x86, microcode, intel: defend apply_microcode_intel
 with BUG_ON

On Fri, 07 Nov 2014, Borislav Petkov wrote:
> On Mon, Sep 08, 2014 at 02:37:54PM -0300, Henrique de Moraes Holschuh wrote:
> > Microcode updates that requires an unknown loader should never reach the
> > apply_* functions (the code should have rejected it earlier).  Likewise
> > for an unknown microcode header layout.
> > 
> > Signed-off-by: Henrique de Moraes Holschuh <hmh@....eng.br>
> > ---
> >  arch/x86/kernel/cpu/microcode/intel.c       |    2 ++
> >  arch/x86/kernel/cpu/microcode/intel_early.c |    2 ++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> > index 40caef1..439681f 100644
> > --- a/arch/x86/kernel/cpu/microcode/intel.c
> > +++ b/arch/x86/kernel/cpu/microcode/intel.c
> > @@ -157,6 +157,8 @@ static int apply_microcode_intel(int cpu)
> >  	if (mc_intel == NULL)
> >  		return 0;
> >  
> > +	BUG_ON(mc_intel->hdr.hdrver != 1 || mc_intel->hdr.ldrver != 1);
> > +
> >  	/* Intel SDM vol 3A section 9.11.6, page 9-34 */
> >  	if (WARN_ONCE((unsigned long)(mc_intel->bits) % 16,
> >  		"microcode data incorrectly aligned"))
> > diff --git a/arch/x86/kernel/cpu/microcode/intel_early.c b/arch/x86/kernel/cpu/microcode/intel_early.c
> > index 994c59b..095db11 100644
> > --- a/arch/x86/kernel/cpu/microcode/intel_early.c
> > +++ b/arch/x86/kernel/cpu/microcode/intel_early.c
> > @@ -671,6 +671,8 @@ static int apply_microcode_early(struct mc_saved_data *mc_saved_data,
> >  	if (mc_intel == NULL)
> >  		return 0;
> >  
> > +	BUG_ON(mc_intel->hdr.hdrver != 1 || mc_intel->hdr.ldrver != 1);
> > +
> >  	mcu_data = mc_intel->bits;
> >  	aligned_mcu_data = mc_intel->bits;
> 
> Both not needed, because we're running all microcode through
> microcode_sanity_check() first which already does that check.

Yeah, that's why it is BUG_ON().

But if you feel this is too defensive, I will just drop this patch.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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