Re: [Xen-devel] [PATCH] x86/PV: restrict permitted instructions during memory write emulation

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/01/17 15:26, Jan Beulich wrote:
> All three code paths mean to only emulate memory writes. Refuse
> emulation of any other instructions there.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> This would effectively allow us to revert 0e47f92b07 ("x86: force
> EFLAGS.IF on when exiting to PV guests").
>
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -5340,11 +5340,19 @@ static int ptwr_emulated_cmpxchg(
>          container_of(ctxt, struct ptwr_emulate_ctxt, ctxt));
>  }
>  
> +static int pv_emul_is_mem_write(const struct x86_emulate_state *state,
> +                                struct x86_emulate_ctxt *ctxt)
> +{
> +    return x86_insn_is_mem_write(state, ctxt) ? X86EMUL_OKAY
> +                                              : X86EMUL_UNHANDLEABLE;
> +}
> +
>  static const struct x86_emulate_ops ptwr_emulate_ops = {
>      .read       = ptwr_emulated_read,
>      .insn_fetch = ptwr_emulated_read,
>      .write      = ptwr_emulated_write,
>      .cmpxchg    = ptwr_emulated_cmpxchg,
> +    .validate   = pv_emul_is_mem_write,

.validate = x86_insn_is_mem_write,  ?

~Andrew

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