[PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb()

From: Joerg Roedel <joro@8bytes.org>
To: x86@kernel.org, Hyunwook Baek <baekhw@google.com>
Cc: Joerg Roedel <joro@8bytes.org>, Joerg Roedel <jroedel@suse.de>,
	stable@vger.kernel.org, hpa@zytor.com,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Slaby <jslaby@suse.cz>,
	Dan Williams <dan.j.williams@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Juergen Gross <jgross@suse.com>,
	Kees Cook <keescook@chromium.org>,
	David Rientjes <rientjes@google.com>,
	Cfir Cohen <cfir@google.com>, Erdem Aktas <erdemaktas@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mike Stunes <mstunes@vmware.com>,
	Sean Christopherson <seanjc@google.com>,
	Martin Radev <martin.b.radev@gmail.com>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb()
Date: Wed, 12 May 2021 09:54:40 +0200	[thread overview]
Message-ID: <20210512075445.18935-2-joro@8bytes.org> (raw)
In-Reply-To: <20210512075445.18935-1-joro@8bytes.org>

From: Joerg Roedel <jroedel@suse.de>

The sev_es_get_ghcb() is called from several places, but only one of
them checks the return value. The reaction to returning NULL is always
the same: Calling panic() and kill the machine.

Instead of adding checks to all call-places, move the panic() into the
function itself so that it will no longer return NULL.

Fixes: 0786138c78e7 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/sev.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 9578c82832aa..c49270c7669e 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -203,8 +203,18 @@ static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
 	if (unlikely(data->ghcb_active)) {
 		/* GHCB is already in use - save its contents */
 
-		if (unlikely(data->backup_ghcb_active))
-			return NULL;
+		if (unlikely(data->backup_ghcb_active)) {
+			/*
+			 * Backup-GHCB is also already in use. There is no way
+			 * to continue here so just kill the machine. To make
+			 * panic() work, mark GHCBs inactive so that messages
+			 * can be printed out.
+			 */
+			data->ghcb_active        = false;
+			data->backup_ghcb_active = false;
+
+			panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
+		}
 
 		/* Mark backup_ghcb active before writing to it */
 		data->backup_ghcb_active = true;
@@ -1284,7 +1294,6 @@ static __always_inline bool on_vc_fallback_stack(struct pt_regs *regs)
  */
 DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 {
-	struct sev_es_runtime_data *data = this_cpu_read(runtime_data);
 	irqentry_state_t irq_state;
 	struct ghcb_state state;
 	struct es_em_ctxt ctxt;
@@ -1310,16 +1319,6 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 	 */
 
 	ghcb = sev_es_get_ghcb(&state);
-	if (!ghcb) {
-		/*
-		 * Mark GHCBs inactive so that panic() is able to print the
-		 * message.
-		 */
-		data->ghcb_active        = false;
-		data->backup_ghcb_active = false;
-
-		panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
-	}
 
 	vc_ghcb_invalidate(ghcb);
 	result = vc_init_em_ctxt(&ctxt, regs, error_code);
-- 
2.31.1

