linux-kernel - Re: [PATCH v2] x86/microcode: Handle negative microcode revisions

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Message-ID: <20181025235102.GK6218@tassilo.jf.intel.com>
Date:   Thu, 25 Oct 2018 16:51:02 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/microcode: Handle negative microcode revisions

On Sat, Oct 20, 2018 at 07:41:36PM +0200, Borislav Petkov wrote:
> Dropping stable.
> 
> On Sat, Oct 20, 2018 at 07:41:58AM -0700, Andi Kleen wrote:
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > The Intel microcode revision space is unsigned. Inside Intel there are special
> > microcodes that have the highest bit set, and they are considered to have
> > a higher revision than any microcodes that don't have this bit set.
> > 
> > The function comparing the microcode revision in the Linux driver compares
> > u32 with int, which ends up being signed extended to long on 64bit
> > systems. This results in these highest bit set microcode revision not loading
> > because their revision appears negative and smaller than the
> > existing microcode.
> > 
> > Change the comparison to unsigned. With that the loading works
> > as expected.
> > 
> > Cc: stable@...r.kernel.org # Any supported stable
> > Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> > --
> > v2: White space changes.
> > ---
> >  arch/x86/kernel/cpu/microcode/intel.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> > index 16936a24795c..e54d402500d3 100644
> > --- a/arch/x86/kernel/cpu/microcode/intel.c
> > +++ b/arch/x86/kernel/cpu/microcode/intel.c
> > @@ -93,7 +93,8 @@ static int find_matching_signature(void *mc, unsigned int csig, int cpf)
> >  /*
> >   * Returns 1 if update has been found, 0 otherwise.
> >   */
> > -static int has_newer_microcode(void *mc, unsigned int csig, int cpf, int new_rev)
> > +static int has_newer_microcode(void *mc, unsigned int csig, int cpf,
> > +			       unsigned new_rev)
> >  {
> >  	struct microcode_header_intel *mc_hdr = mc;
> >  
> > -- 
> 
> Please incorporate all review comments before sending a new version of
> your patch.

I replaced one more microcodes with microcodes revisions if that is
what you meant.

-Andi