[PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

[PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

[Hyunwook (Wooky) Baek]

Don't assume dest/source buffers are userspace addresses when manually
copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
if handed a kernel address and ultimately lead to a kernel panic.

Signed-off-by: Hyunwook (Wooky) Baek <baekhw@google.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 arch/x86/kernel/sev-es.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0bd1a0fc587e..812494d216ba 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -286,6 +286,12 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
+	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
+	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
+		memcpy(dst, buf, size);
+		return ES_OK;
+	}
+
 	switch (size) {
 	case 1:
 		memcpy(&d1, buf, 1);
@@ -335,6 +341,12 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
+	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
+	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
+		memcpy(buf, src, size);
+		return ES_OK;
+	}
+
 	switch (size) {
 	case 1:
 		if (get_user(d1, s))
-- 
2.29.2.729.g45daf8777d-goog

Re: [PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

[Borislav Petkov]

On Thu, Jan 07, 2021 at 06:51:07PM -0800, Hyunwook (Wooky) Baek wrote:
> Don't assume dest/source buffers are userspace addresses when manually
> copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
> if handed a kernel address and ultimately lead to a kernel panic.
> 
> Signed-off-by: Hyunwook (Wooky) Baek <baekhw@google.com>
> Acked-by: David Rientjes <rientjes@google.com>
> ---
>  arch/x86/kernel/sev-es.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 0bd1a0fc587e..812494d216ba 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -286,6 +286,12 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
>  	u16 d2;
>  	u8  d1;
>  
> +	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
> +	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
						^^^

Just by looking at this patch I know you haven't tested it before sending.

:-(

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

[Hyunwook (Wooky) Baek]

Hi Borisslav,

My sincere apologies for it.
We actually tested the patch but I made a bad mistake while generating
the patch file to email.
I will send a PATCH V2 after testing the email version patch file from
the scratch.

Regards,
Wooky

On Fri, Jan 8, 2021 at 9:20 AM Borislav Petkov <bp@alien8.de> wrote:
>
> On Thu, Jan 07, 2021 at 06:51:07PM -0800, Hyunwook (Wooky) Baek wrote:
> > Don't assume dest/source buffers are userspace addresses when manually
> > copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
> > if handed a kernel address and ultimately lead to a kernel panic.
> >
> > Signed-off-by: Hyunwook (Wooky) Baek <baekhw@google.com>
> > Acked-by: David Rientjes <rientjes@google.com>
> > ---
> >  arch/x86/kernel/sev-es.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> > index 0bd1a0fc587e..812494d216ba 100644
> > --- a/arch/x86/kernel/sev-es.c
> > +++ b/arch/x86/kernel/sev-es.c
> > @@ -286,6 +286,12 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
> >       u16 d2;
> >       u8  d1;
> >
> > +     /* If instruction ran in kernel mode and the I/O buffer is in kernel space */
> > +     if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
>                                                 ^^^
>
> Just by looking at this patch I know you haven't tested it before sending.
>
> :-(
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette