linux-kernel - [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get

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Date:   Wed, 12 May 2021 09:54:40 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org, Hyunwook Baek <baekhw@...gle.com>
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        stable@...r.kernel.org, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb()

From: Joerg Roedel <jroedel@...e.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@...r.kernel.org # v5.10+
Signed-off-by: Joerg Roedel <jroedel@...e.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