linux-kernel - [PATCH 44/70] x86/sev-es: Handle instruction fetches from user-space

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Message-Id: <20200319091407.1481-45-joro@8bytes.org>
Date:   Thu, 19 Mar 2020 10:13:41 +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 44/70] x86/sev-es: Handle instruction fetches from user-space

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

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>
---
 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 226ab0c57a09..79a71d14a1fc 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -114,17 +114,30 @@ 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 = 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;
+		}
+
+		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
+		insn_get_length(&ctxt->insn);
+	} else {
+		res = insn_fetch_from_user(ctxt->regs, buffer);
+		if (res == 0) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.cr2        = ctxt->regs->ip;
+			ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+			return ES_EXCEPTION;
+		}
+
+		if (!insn_decode(ctxt->regs, &ctxt->insn, buffer, res))
+			return ES_DECODE_FAILED;
 	}
 
-	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;
-- 
2.17.1