linux-kernel - [PATCH 4.19 39/39] x86/insn-eval: Use new for_each_insn_prefix() macro to loop over prefixes bytes

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Message-Id: <20201210142604.214845768@linuxfoundation.org>
Date:   Thu, 10 Dec 2020 15:27:18 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+9b64b619f10f19d19a7c@...kaller.appspotmail.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: [PATCH 4.19 39/39] x86/insn-eval: Use new for_each_insn_prefix() macro to loop over prefixes bytes

From: Masami Hiramatsu <mhiramat@...nel.org>

commit 12cb908a11b2544b5f53e9af856e6b6a90ed5533 upstream

Since insn.prefixes.nbytes can be bigger than the size of
insn.prefixes.bytes[] when a prefix is repeated, the proper check must
be

  insn.prefixes.bytes[i] != 0 and i < 4

instead of using insn.prefixes.nbytes. Use the new
for_each_insn_prefix() macro which does it correctly.

Debugged by Kees Cook <keescook@...omium.org>.

 [ bp: Massage commit message. ]

Fixes: 32d0b95300db ("x86/insn-eval: Add utility functions to get segment selector")
Reported-by: syzbot+9b64b619f10f19d19a7c@...kaller.appspotmail.com
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/160697104969.3146288.16329307586428270032.stgit@devnote2
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/lib/insn-eval.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -70,14 +70,15 @@ static int get_seg_reg_override_idx(stru
 {
 	int idx = INAT_SEG_REG_DEFAULT;
 	int num_overrides = 0, i;
+	insn_byte_t p;
 
 	insn_get_prefixes(insn);
 
 	/* Look for any segment override prefixes. */
-	for (i = 0; i < insn->prefixes.nbytes; i++) {
+	for_each_insn_prefix(insn, i, p) {
 		insn_attr_t attr;
 
-		attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]);
+		attr = inat_get_opcode_attribute(p);
 		switch (attr) {
 		case INAT_MAKE_PREFIX(INAT_PFX_CS):
 			idx = INAT_SEG_REG_CS;