linux-kernel - [PATCH 38/62] x86/sev-es: Handle instruction fetches from user-space

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Date:   Tue, 11 Feb 2020 14:52:32 +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 38/62] 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 es_fetch_insn_byte() to safely fetch kernel and user
instruction bytes.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/sev-es.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 2a801919e7c0..f5bff4219f6f 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -61,13 +61,29 @@ static enum es_result es_fetch_insn_byte(struct es_em_ctxt *ctxt,
 					 unsigned int offset,
 					 char *buffer)
 {
-	char *rip = (char *)ctxt->regs->ip;
-
-	/* More checks are needed when we boot to user-space */
-	if (!check_kernel(ctxt->regs))
-		return ES_UNSUPPORTED;
-
-	buffer[offset] = rip[offset];
+	if (user_mode(ctxt->regs)) {
+		unsigned long addr = ctxt->regs->ip + offset;
+		char __user *rip = (char __user *)addr;
+
+		if (unlikely(addr >= TASK_SIZE_MAX))
+			return ES_UNSUPPORTED;
+
+		if (copy_from_user(buffer + offset, rip, 1)) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.cr2        = addr;
+			ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+			return ES_EXCEPTION;
+		}
+	} else {
+		char *rip = (char *)ctxt->regs->ip + offset;
+
+		if (probe_kernel_read(buffer + offset, rip, 1) != 0) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.cr2        = (unsigned long)rip;
+			ctxt->fi.error_code = X86_PF_INSTR;
+			return ES_EXCEPTION;
+		}
+	}
 
 	return ES_OK;
 }
-- 
2.17.1