linux-kernel - [PATCH v2 3/3] x86/sev-es: Fix not using prefixes.nbytes for loop over prefixes.bytes

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Date:   Thu,  3 Dec 2020 13:51:01 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] x86/sev-es: Fix not using prefixes.nbytes for loop over prefixes.bytes

Since the insn.prefixes.nbytes can be bigger than the size of
insn.prefixes.bytes[] when a same prefix is repeated, we have to
check whether the i < 4 and insn.prefixes.bytes[i] != 0 instead
of insn.prefixes.nbytes.

Fixes: 25189d08e516 ("x86/sev-es: Add support for handling IOIO exceptions")
Reported-by: syzbot+9b64b619f10f19d19a7c@...kaller.appspotmail.com
Debugged-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/x86/boot/compressed/sev-es.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
index 954cb2702e23..27826c265aab 100644
--- a/arch/x86/boot/compressed/sev-es.c
+++ b/arch/x86/boot/compressed/sev-es.c
@@ -32,13 +32,12 @@ struct ghcb *boot_ghcb;
  */
 static bool insn_has_rep_prefix(struct insn *insn)
 {
+	insn_byte_t p;
 	int i;
 
 	insn_get_prefixes(insn);
 
-	for (i = 0; i < insn->prefixes.nbytes; i++) {
-		insn_byte_t p = insn->prefixes.bytes[i];
-
+	for_each_insn_prefix(insn, i, p) {
 		if (p == 0xf2 || p == 0xf3)
 			return true;
 	}