Re: [PATCH v2] x86/microcode: Handle negative microcode revisions
From: Borislav Petkov
Date: Sat Oct 20 2018 - 13:42:15 EST
On Sat, Oct 20, 2018 at 07:41:58AM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxx # Any supported stable
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 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;
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