linux-kernel - [PATCH 40/62] x86/sev-es: Filter exceptions not supported from user-space

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Message-Id: <20200211135256.24617-41-joro@8bytes.org>
Date:   Tue, 11 Feb 2020 14:52:34 +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 40/62] x86/sev-es: Filter exceptions not supported from user-space

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

Currently only CPUID caused #VC exceptions are supported from
user-space. Filter the others out early.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/sev-es.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index d128a9397639..84b5b8f7897a 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -209,6 +209,26 @@ static enum es_result handle_vc_exception(struct es_em_ctxt *ctxt,
 	return result;
 }
 
+static enum es_result context_filter(struct pt_regs *regs, long exit_code)
+{
+	enum es_result r = ES_OK;
+
+	if (user_mode(regs)) {
+		switch (exit_code) {
+		/* List of #VC exit-codes we support in user-space */
+		case SVM_EXIT_EXCP_BASE ... SVM_EXIT_LAST_EXCP:
+		case SVM_EXIT_CPUID:
+			r = ES_OK;
+			break;
+		default:
+			r = ES_UNSUPPORTED;
+			break;
+		}
+	}
+
+	return r;
+}
+
 static void forward_exception(struct es_em_ctxt *ctxt)
 {
 	long error_code = ctxt->fi.error_code;
@@ -245,6 +265,10 @@ dotraplinkage void do_vmm_communication(struct pt_regs *regs, unsigned long exit
 	ghcb_invalidate(ghcb);
 	result = init_em_ctxt(&ctxt, regs, exit_code);
 
+	/* Check if the exception is supported in the context we came from. */
+	if (result == ES_OK)
+		result = context_filter(regs, exit_code);
+
 	if (result == ES_OK)
 		result = handle_vc_exception(&ctxt, ghcb, exit_code);
 
-- 
2.17.1