[tip: x86/urgent] x86/insn-eval: Use new for_each_insn_prefix() macro to loop over prefixes bytes

[tip-bot2 for Masami Hiramatsu]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     12cb908a11b2544b5f53e9af856e6b6a90ed5533
Gitweb:        https://git.kernel.org/tip/12cb908a11b2544b5f53e9af856e6b6a90ed5533
Author:        Masami Hiramatsu <mhiramat@xxxxxxxxxx>
AuthorDate:    Thu, 03 Dec 2020 13:50:50 +09:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Sun, 06 Dec 2020 10:03:08 +01:00

x86/insn-eval: Use new for_each_insn_prefix() macro to loop over prefixes bytes

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@xxxxxxxxxxxx>.

 [ bp: Massage commit message. ]

Fixes: 32d0b95300db ("x86/insn-eval: Add utility functions to get segment selector")
Reported-by: syzbot+9b64b619f10f19d19a7c@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/160697104969.3146288.16329307586428270032.stgit@devnote2
---
 arch/x86/lib/insn-eval.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 58f7fb9..4229950 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -63,13 +63,12 @@ static bool is_string_insn(struct insn *insn)
  */
 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;
 	}
@@ -95,14 +94,15 @@ static int get_seg_reg_override_idx(struct insn *insn)
 {
 	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;