linux-kernel - [PATCH 39/62] x86/sev-es: Harden runtime #VC handler for exceptions from user-space

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Message-Id: <20200211135256.24617-40-joro@8bytes.org>
Date:   Tue, 11 Feb 2020 14:52:33 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        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>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 39/62] x86/sev-es: Harden runtime #VC handler for exceptions from user-space

From: Joerg Roedel <jroedel@...e.de>

Send SIGBUS to the user-space process that caused the #VC exception
instead of killing the machine. Also ratelimit the error messages so
that user-space can't flood the kernel log.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/sev-es.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index f5bff4219f6f..d128a9397639 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -254,16 +254,16 @@ dotraplinkage void do_vmm_communication(struct pt_regs *regs, unsigned long exit
 		finish_insn(&ctxt);
 		break;
 	case ES_UNSUPPORTED:
-		pr_emerg("Unsupported exit-code 0x%02lx in early #VC exception (IP: 0x%lx)\n",
-			 exit_code, regs->ip);
+		pr_err_ratelimited("Unsupported exit-code 0x%02lx in early #VC exception (IP: 0x%lx)\n",
+				   exit_code, regs->ip);
 		goto fail;
 	case ES_VMM_ERROR:
-		pr_emerg("PANIC: Failure in communication with VMM (exit-code 0x%02lx IP: 0x%lx)\n",
-			 exit_code, regs->ip);
+		pr_err_ratelimited("Failure in communication with VMM (exit-code 0x%02lx IP: 0x%lx)\n",
+				   exit_code, regs->ip);
 		goto fail;
 	case ES_DECODE_FAILED:
-		pr_emerg("PANIC: Failed to decode instruction (exit-code 0x%02lx IP: 0x%lx)\n",
-			 exit_code, regs->ip);
+		pr_err_ratelimited("PANIC: Failed to decode instruction (exit-code 0x%02lx IP: 0x%lx)\n",
+				   exit_code, regs->ip);
 		goto fail;
 	case ES_EXCEPTION:
 		forward_exception(&ctxt);
@@ -278,10 +278,24 @@ dotraplinkage void do_vmm_communication(struct pt_regs *regs, unsigned long exit
 	return;
 
 fail:
-	show_regs(regs);
+	if (user_mode(regs)) {
+		/*
+		 * Do not kill the machine if user-space triggered the
+		 * exception. Send SIGBUS instead and let user-space deal with
+		 * it.
+		 */
+		force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
+	} else {
+		/* Show some debug info */
+		show_regs(regs);
 
-	while (true)
-		halt();
+		/* Ask hypervisor to terminate */
+		terminate(GHCB_SEV_ES_REASON_GENERAL_REQUEST);
+
+		/* If that fails and we get here - just halt the machine */
+		while (true)
+			halt();
+	}
 }
 
 int __init boot_vc_exception(struct pt_regs *regs)
-- 
2.17.1