Re: [PATCH v3 2/4] x86/traps: Print non-canonical address on #GP

[Sean Christopherson]

On Wed, Nov 20, 2019 at 02:39:13PM +0100, Borislav Petkov wrote:
> On Wed, Nov 20, 2019 at 02:28:30PM +0100, Ingo Molnar wrote:
> > I'd rather we not trust the decoder and the execution environment so much 
> > that it never produces a 0 linear address in a #GP:
> 
> I was just scratching my head whether I could trigger a #GP with address
> of 0. But yeah, I agree, let's be really cautious here. I wouldn't want
> to debug a #GP with a wrong address reported.

It's definitely possible, there are a handful of non-SIMD instructions that
generate #GP(0) it CPL=0 in 64-bit mode *and* have a memory operand.  Some
of them might even be legitimately encountered in the wild.

  - CMPXCHG16B if it's not supported by the CPU.
  - VMXON if CR4 is misconfigured or VMX isn't enabled in FEATURE_CONTROL.
  - MONITOR if ECX has an invalid hint (although MONITOR hardcodes the
    address in DS:RAX and so doesn't have a ModR/M byte).

Undoudbtedly there are other instructions with similar sources of #GP.