linux-kernel - [tip: x86/seves] x86/sev-es: Handle instruction fetches from user-space

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Date:   Thu, 10 Sep 2020 09:22:12 -0000
From:   "tip-bot2 for Joerg Roedel" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Joerg Roedel <jroedel@...e.de>, Borislav Petkov <bp@...e.de>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/seves] x86/sev-es: Handle instruction fetches from user-space

The following commit has been merged into the x86/seves branch of tip:

Commit-ID:     5e3427a7bc432ed2e5de394ac30f160cc6c37a1f
Gitweb:        https://git.kernel.org/tip/5e3427a7bc432ed2e5de394ac30f160cc6c37a1f
Author:        Joerg Roedel <jroedel@...e.de>
AuthorDate:    Mon, 07 Sep 2020 15:15:49 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 09 Sep 2020 11:33:19 +02:00

x86/sev-es: Handle instruction fetches from user-space

When a #VC exception is triggered by user-space, the instruction decoder
needs to read the instruction bytes from user addresses. Enhance
vc_decode_insn() to safely fetch kernel and user instructions.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-49-joro@8bytes.org
---
 arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index b10a62a..6c30dbc 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -232,17 +232,30 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
 	enum es_result ret;
 	int res;
 
-	res = vc_fetch_insn_kernel(ctxt, buffer);
-	if (unlikely(res == -EFAULT)) {
-		ctxt->fi.vector     = X86_TRAP_PF;
-		ctxt->fi.error_code = 0;
-		ctxt->fi.cr2        = ctxt->regs->ip;
-		return ES_EXCEPTION;
+	if (user_mode(ctxt->regs)) {
+		res = insn_fetch_from_user(ctxt->regs, buffer);
+		if (!res) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+			ctxt->fi.cr2        = ctxt->regs->ip;
+			return ES_EXCEPTION;
+		}
+
+		if (!insn_decode(&ctxt->insn, ctxt->regs, buffer, res))
+			return ES_DECODE_FAILED;
+	} else {
+		res = vc_fetch_insn_kernel(ctxt, buffer);
+		if (res) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.error_code = X86_PF_INSTR;
+			ctxt->fi.cr2        = ctxt->regs->ip;
+			return ES_EXCEPTION;
+		}
+
+		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
+		insn_get_length(&ctxt->insn);
 	}
 
-	insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
-	insn_get_length(&ctxt->insn);
-
 	ret = ctxt->insn.immediate.got ? ES_OK : ES_DECODE_FAILED;
 
 	return ret;