x86/sev-es: Invalidate the GHCB after completing VMGEXIT

commit a50c5bebc99c525e7fbc059988c6a5ab8680cb76 upstream.

Since the VMGEXIT instruction can be issued from userspace, invalidate
the GHCB after performing VMGEXIT processing in the kernel.

Invalidation is only required after userspace is available, so call
vc_ghcb_invalidate() from sev_es_put_ghcb(). Update vc_ghcb_invalidate()
to additionally clear the GHCB exit code so that it is always presented
as 0 when VMGEXIT has been issued by anything else besides the kernel.

Fixes: 0786138c78e79 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/5a8130462e4f0057ee1184509cd056eedd78742b.1621273353.git.thomas.lendacky@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/sev-es-shared.c b/arch/x86/kernel/sev-es-shared.c
index 387b716698187bc4ce67655b3a3edf1e4c703423..ecb20b17b7df611984d7254210512234cbfe44d2 100644 (file)
--- a/arch/x86/kernel/sev-es-shared.c
+++ b/arch/x86/kernel/sev-es-shared.c
@@ -63,6 +63,7 @@ static bool sev_es_negotiate_protocol(void)
 
 static __always_inline void vc_ghcb_invalidate(struct ghcb *ghcb)
 {
+       ghcb->save.sw_exit_code = 0;
        memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
 }
 

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 24a4a1cfdbd12eef7c3eb43243cdaecc12cdde20..87a9d848b58b781ce1c3bdaf483c1b10e6be67c1 100644 (file)
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -430,6 +430,11 @@ static __always_inline void sev_es_put_ghcb(struct ghcb_state *state)
                data->backup_ghcb_active = false;
                state->ghcb = NULL;
        } else {
+               /*
+                * Invalidate the GHCB so a VMGEXIT instruction issued
+                * from userspace won't appear to be valid.
+                */
+               vc_ghcb_invalidate(ghcb);
                data->ghcb_active = false;
        }
 }