2021-09-13 15:59:31

by Joerg Roedel

Subject: [PATCH v2 05/12] x86/sev: Use GHCB protocol version 2 if supported

From: Joerg Roedel <[email protected]>

Check whether the hypervisor supports GHCB version 2 and use it if
available.

Signed-off-by: Joerg Roedel <[email protected]>
---
arch/x86/boot/compressed/sev.c | 10 ++++++++--
arch/x86/include/asm/sev.h | 4 ++--
arch/x86/kernel/sev-shared.c | 17 ++++++++++++++---
3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 101e08c67296..7f8416f76be7 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -119,16 +119,22 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
/* Include code for early handlers */
#include "../../kernel/sev-shared.c"

+static unsigned int ghcb_protocol;
+
static u64 sev_get_ghcb_proto_ver(void)
{
- return GHCB_PROTOCOL_MAX;
+ return ghcb_protocol;
}

static bool early_setup_sev_es(void)
{
- if (!sev_es_negotiate_protocol(NULL))
+ struct sev_ghcb_protocol_info info;
+
+ if (!sev_es_negotiate_protocol(&info))
sev_es_terminate(GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED);

+ ghcb_protocol = info.vm_proto;
+
if (set_page_decrypted((unsigned long)&boot_ghcb_page))
return false;

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index fa5cd05d3b5b..134a7c9d91b6 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -12,8 +12,8 @@
#include <asm/insn.h>
#include <asm/sev-common.h>

-#define GHCB_PROTO_OUR 0x0001UL
-#define GHCB_PROTOCOL_MAX 1ULL
+#define GHCB_PROTOCOL_MIN 1ULL
+#define GHCB_PROTOCOL_MAX 2ULL
#define GHCB_DEFAULT_USAGE 0ULL

#define VMGEXIT() { asm volatile("rep; vmmcall\n\r"); }
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 36eaac2773ed..40a1ca81bdb8 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -61,6 +61,7 @@ static void __noreturn sev_es_terminate(unsigned int reason)

static bool sev_es_negotiate_protocol(struct sev_ghcb_protocol_info *info)
{
+ unsigned int protocol;
u64 val;

/* Do the GHCB protocol version negotiation */
@@ -71,14 +72,24 @@ static bool sev_es_negotiate_protocol(struct sev_ghcb_protocol_info *info)
if (GHCB_MSR_INFO(val) != GHCB_MSR_SEV_INFO_RESP)
return false;

- if (GHCB_MSR_PROTO_MAX(val) < GHCB_PROTO_OUR ||
- GHCB_MSR_PROTO_MIN(val) > GHCB_PROTO_OUR)
+ /* Sanity check untrusted input */
+ if (GHCB_MSR_PROTO_MIN(val) > GHCB_MSR_PROTO_MAX(val))
+ return false;
+
+ /* Use maximum supported protocol version */
+ protocol = min_t(unsigned int, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);
+
+ /*
+ * Hypervisor does not support any protocol version required for this
+ * kernel.
+ */
+ if (protocol < GHCB_MSR_PROTO_MIN(val))
return false;

if (info) {
info->hv_proto_min = GHCB_MSR_PROTO_MIN(val);
info->hv_proto_max = GHCB_MSR_PROTO_MAX(val);
- info->vm_proto = GHCB_PROTO_OUR;
+ info->vm_proto = protocol;
}

return true;
--
2.33.0

2021-11-03 16:06:58

by Borislav Petkov

Subject: Re: [PATCH v2 05/12] x86/sev: Use GHCB protocol version 2 if supported

On Mon, Sep 13, 2021 at 05:55:56PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <[email protected]>
>
> Check whether the hypervisor supports GHCB version 2 and use it if
> available.
>
> Signed-off-by: Joerg Roedel <[email protected]>
> ---
> arch/x86/boot/compressed/sev.c | 10 ++++++++--
> arch/x86/include/asm/sev.h | 4 ++--
> arch/x86/kernel/sev-shared.c | 17 ++++++++++++++---
> 3 files changed, 24 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 101e08c67296..7f8416f76be7 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -119,16 +119,22 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
> /* Include code for early handlers */
> #include "../../kernel/sev-shared.c"
>
> +static unsigned int ghcb_protocol;

I guess you need to sync up with Brijesh on what to use:

https://lore.kernel.org/r/[email protected]

And if ghcb_version there is __ro_after_init I think that's perfectly
fine and doesn't need an accessor...

Thx.

--
Regards/Gruss,
Boris.

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