[PATCH v1] x86/microcode: Handle negative microcode revisions

[PATCH v1] x86/microcode: Handle negative microcode revisions

[Andi Kleen]

From: Andi Kleen <ak@linux.intel.com>

The Intel ucode 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 microcodes 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 microcodes 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.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/kernel/cpu/microcode/intel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 16936a24795c..e95cebdd5993 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -93,7 +93,7 @@ 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;
 
-- 
2.17.1

Re: [PATCH v1] x86/microcode: Handle negative microcode revisions

[Borislav Petkov]

On Fri, Oct 19, 2018 at 05:11:37PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> The Intel ucode revision space is unsigned. Inside Intel there are special

s/ucode/microcode/g

> microcodes that have the highest bit set, and they are considered to have

s/microcodes/microcode revisions/g

> a higher revision than any microcodes that don't have this bit set.
> 
> The function comparing the microcodes 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 microcodes 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.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
>  arch/x86/kernel/cpu/microcode/intel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 16936a24795c..e95cebdd5993 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -93,7 +93,7 @@ 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)

I'm gonna let you run checkpatch yourself to find out what the problem
here is.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Re: [PATCH v1] x86/microcode: Handle negative microcode revisions

[Thomas Gleixner]

Andi,

On Fri, 19 Oct 2018, Andi Kleen wrote:
> Change the comparison to unsigned. With that the loading works
> as expected.
>

I assume that wants a fixes tag and needs to be backported to stable,
right?

Thanks,

	tglx

Re: [PATCH v1] x86/microcode: Handle negative microcode revisions

[Andi Kleen]

On Sat, Oct 20, 2018 at 03:42:05PM +0200, Thomas Gleixner wrote:
> Andi,
> 
> On Fri, 19 Oct 2018, Andi Kleen wrote:
> > Change the comparison to unsigned. With that the loading works
> > as expected.
> >
> 
> I assume that wants a fixes tag and needs to be backported to stable,
> right?

I think the bug was there since the original microcode loader, not
sure I can dig out the right commit id for that (it might be
in linux-historic)

Yes please cc stable for this.

-Andi