linux-kernel - [PATCH v2 2/2] x86/sev-es: Invalidate the GHCB after completing VMGEXIT

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Message-Id: <5a8130462e4f0057ee1184509cd056eedd78742b.1621273353.git.thomas.lendacky@amd.com>
Date:   Mon, 17 May 2021 12:42:33 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Brijesh Singh <brijesh.singh@....com>, stable@...r.kernel.org
Subject: [PATCH v2 2/2] x86/sev-es: Invalidate the GHCB after completing VMGEXIT

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 a value of 0 is always
present outside VMGEXIT processing in the kernel.

Fixes: 0786138c78e79 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc: stable@...r.kernel.org
Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/kernel/sev-shared.c | 1 +
 arch/x86/kernel/sev.c        | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 6ec8b3bfd76e..9f90f460a28c 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-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.c b/arch/x86/kernel/sev.c
index 45e212675811..4fa111becc93 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -457,6 +457,11 @@ 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;
 	}
 }
-- 
2.31.0