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From:   Joerg Roedel <joro@8bytes.org>
To:     x86@kernel.org
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Subject: [PATCH v4 50/75] x86/sev-es: Handle instruction fetches from user-space
Date:   Tue, 14 Jul 2020 14:08:52 +0200
Message-Id: <20200714120917.11253-51-joro@8bytes.org>
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From: Joerg Roedel <jroedel@suse.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@suse.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 e04a1868905b..08b66fd5ae9a 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -247,17 +247,30 @@ 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;
-- 
2.27.0