From: Borislav Petkov <bp@alien8.de>
To: Sean Christopherson <seanjc@google.com>, Peter Gonda <pgonda@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
Tom Lendacky <thomas.lendacky@amd.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH] x86/sev-es: Fix SEV-ES OUT/IN immediate opcode vc handling
Date: Mon, 28 Dec 2020 23:36:50 +0100 [thread overview]
Message-ID: <20201228223650.GD20321@zn.tnic> (raw)
In-Reply-To: <X9uTESe5n3ApvnOD@google.com>
On Thu, Dec 17, 2020 at 09:19:13AM -0800, Sean Christopherson wrote:
> On Wed, Dec 16, 2020, Peter Gonda wrote:
> >
> > The IN and OUT immediate instructions only use an 8-bit immediate. The
> > current VC handler uses the entire 32-bit immediate value. These
> > instructions only set the first bytes.
> >
> > Tested with a loop back port with "outb %0,$0xe0". Before the port seen
> > by KVM was 0xffffffffffffffe0 instead of 0xe0. After the correct port
> > was seen by KVM and the guests loop back OUT then IN were equal.
> >
> >
> > Signed-off-by: Peter Gonda <pgonda@google.com>
> > Acked-by: David Rientjes <rientjes@google.com>
> >
> >
> > ---
> > arch/x86/kernel/sev-es-shared.c | 8 ++++++--
> > drivers/Makefile | 1 +
> > 2 files changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/sev-es-shared.c b/arch/x86/kernel/sev-es-shared.c
> > index 7d04b356d44d..6c790377c55c 100644
> > --- a/arch/x86/kernel/sev-es-shared.c
> > +++ b/arch/x86/kernel/sev-es-shared.c
> > @@ -305,14 +305,14 @@ static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo)
> > case 0xe4:
> > case 0xe5:
> > *exitinfo |= IOIO_TYPE_IN;
> > - *exitinfo |= (u64)insn->immediate.value << 16;
> > + *exitinfo |= insn->immediate.bytes[0] << 16;
>
> Can't we just drop the explicit cast to u64? Or explicitly cast to u8? Doesn't
> really matter, but poking into the backing bytes feels a bit backwards.
GHCB spec says for IOIO_PROT (exit code 0x7b):
"SW_EXITINFO1 will be set as documented in AMD64 Architecture
Programmer’s Manual Volume 2: System Programming, Section 15.10.2"
That section has "Figure 15-2. EXITINFO1 for IOIO Intercept" where
[31:16] is the intercepted I/O port.
Now, insn->immediate.value is a union between a signed int and a
unsigned char bytes[4] array so in order to be absolutely correct, that
should use:
insn->immediate.bytes[0]
instead, to get the port byte only, before shifting it into [31:16]. The
(u64) cast doesn't matter because *exitinfo = 0 at function entry and
that is part of the first assignment afterwards.
I still don't see how that sign extension 0xffffffffffffffe0 can happen,
though. Maybe something gets added during instruction decoding...
Hmmm.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-12-28 22:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 1:04 [PATCH] x86/sev-es: Fix SEV-ES OUT/IN immediate opcode vc handling Peter Gonda
2020-12-17 17:19 ` Sean Christopherson
2020-12-28 22:36 ` Borislav Petkov [this message]
2020-12-28 23:43 ` Sean Christopherson
2020-12-29 10:56 ` Borislav Petkov
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