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 <[email protected]>
Acked-by: David Rientjes <[email protected]>
---
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;
break;
/* OUT immediate opcodes */
case 0xe6:
case 0xe7:
*exitinfo |= IOIO_TYPE_OUT;
- *exitinfo |= (u64)insn->immediate.value << 16;
+ *exitinfo |= insn->immediate.bytes[0] << 16;
break;
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 <[email protected]>
> Acked-by: David Rientjes <[email protected]>
>
>
> ---
> 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.
> break;
>
> /* OUT immediate opcodes */
> case 0xe6:
> case 0xe7:
> *exitinfo |= IOIO_TYPE_OUT;
> - *exitinfo |= (u64)insn->immediate.value << 16;
> + *exitinfo |= insn->immediate.bytes[0] << 16;
> break;
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 <[email protected]>
> > Acked-by: David Rientjes <[email protected]>
> >
> >
> > ---
> > 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
On Mon, Dec 28, 2020, Borislav Petkov wrote:
> 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 <[email protected]>
> > > Acked-by: David Rientjes <[email protected]>
> > >
> > >
> > > ---
> > > 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]
Eh, casting to u8 is "absolutely correct" as well. I don't like using bytes[]
because it feels like accessing the raw data as opposed to the end result of
decoding, but it's not a sticking point.
> (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...
Yes, insn_get_immediate() sets insn->immediate.value directly and sign extends
the imm8 (which is correct, e.g. for "AND r/m64, imm8").
switch (inat_immediate_size(insn->attr)) {
case INAT_IMM_BYTE:
insn->immediate.value = get_next(signed char, insn);
insn->immediate.nbytes = 1;
break;
...
}
>
> Hmmm.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
On Mon, Dec 28, 2020 at 03:43:06PM -0800, Sean Christopherson wrote:
> Eh, casting to u8 is "absolutely correct" as well. I don't like using bytes[]
> because it feels like accessing the raw data as opposed to the end result of
> decoding, but it's not a sticking point.
Ok, code in the kernel uses mostly ->value so u8 casting it is.
> Yes, insn_get_immediate() sets insn->immediate.value directly and sign extends
> the imm8 (which is correct, e.g. for "AND r/m64, imm8").
>
> switch (inat_immediate_size(insn->attr)) {
> case INAT_IMM_BYTE:
> insn->immediate.value = get_next(signed char, insn);
> insn->immediate.nbytes = 1;
Ah, there it is. And we set nbytes too, conveniently.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette