From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: emulate reserved nops from 0f/18 to 0f/1f
Date: Mon, 18 May 2020 09:07:20 -0700 [thread overview]
Message-ID: <20200518160720.GB3632@linux.intel.com> (raw)
In-Reply-To: <20200515161919.29249-1-pbonzini@redhat.com>
On Fri, May 15, 2020 at 12:19:19PM -0400, Paolo Bonzini wrote:
> Instructions starting with 0f18 up to 0f1f are reserved nops, except those
> that were assigned to MPX.
Well, they're probably reserved NOPs again :-D.
> These include the endbr markers used by CET.
And RDSPP. Wouldn't it make sense to treat RDSPP as a #UD even though it's
a NOP if CET is disabled? The logic being that a sane guest will execute
RDSSP iff CET is enabled, and in that case it'd be better to inject a #UD
than to silently break the guest.
Extending that logic to future features, wouldn't it then make sense to
keep the current #UD behavior for all opcodes to avoid silently breakage?
I.e. change only the opcodes for endbr (which consume only 2 of 255 ModRMs
for 0f 1e) to be NOPs.
> List them correctly in the opcode table.
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/emulate.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index de5476f8683e..d0e2825ae617 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4800,8 +4800,12 @@ static const struct opcode twobyte_table[256] = {
> GP(ModRM | DstReg | SrcMem | Mov | Sse, &pfx_0f_10_0f_11),
> GP(ModRM | DstMem | SrcReg | Mov | Sse, &pfx_0f_10_0f_11),
> N, N, N, N, N, N,
> - D(ImplicitOps | ModRM | SrcMem | NoAccess),
> - N, N, N, N, N, N, D(ImplicitOps | ModRM | SrcMem | NoAccess),
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), /* 4 * prefetch + 4 * reserved NOP */
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), N, N,
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), /* 8 * reserved NOP */
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), /* 8 * reserved NOP */
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), /* 8 * reserved NOP */
> + D(ImplicitOps | ModRM | SrcMem | NoAccess), /* NOP + 7 * reserved NOP */
> /* 0x20 - 0x2F */
> DIP(ModRM | DstMem | Priv | Op3264 | NoMod, cr_read, check_cr_read),
> DIP(ModRM | DstMem | Priv | Op3264 | NoMod, dr_read, check_dr_read),
> --
> 2.18.2
>
next prev parent reply other threads:[~2020-05-18 16:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 16:19 [PATCH] KVM: x86: emulate reserved nops from 0f/18 to 0f/1f Paolo Bonzini
2020-05-18 16:07 ` Sean Christopherson [this message]
2020-05-18 17:37 ` Paolo Bonzini
2020-05-19 6:02 ` Sean Christopherson
2020-05-19 7:43 ` Paolo Bonzini
2020-05-19 7:55 ` Sean Christopherson
2020-05-19 8:06 ` Paolo Bonzini
2020-05-19 15:32 ` Sean Christopherson
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