Re: [edk2-devel] [PATCH] OvmfPkg: Harden #VC instruction emulation somewhat (CVE-2024-25742)

["Gerd Hoffmann" <kraxel@redhat.com>]

On Thu, Apr 18, 2024 at 08:39:20AM -0700, Adam Dunlap wrote:
> On Thu, Apr 18, 2024 at 5:15 AM Gerd Hoffmann <kraxel@redhat.com> wrote:
> >
> > On Wed, Apr 17, 2024 at 09:54:00AM -0700, Adam Dunlap via groups.io wrote:
> > > +  UINT8  OpCode;
> >
> > The linux kernel patch uses "unsigned int opcode" and apparently
> > checks more than just the first byte for multi-byte opcodes.  Why
> > do it differently here?
> 
> Good question. This patch does check for two-byte opcodes with this snippet:
> 
> +  OpCode = *(InstructionData->OpCodes);
> +  if (OpCode == TWO_BYTE_OPCODE_ESCAPE) {
> +    OpCode = *(InstructionData->OpCodes + 1);
> +  }
> 
> This works because the first byte of two-byte opcodes is always 0x0f in the
> cases that we're checking for.

Ok, missed that little detail.  Thanks for explaining.

Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd



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