[tip: x86/urgent] x86/sev-es: 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:     46a4ad7814fa39971aa6549b30c1a08d5c2ec65f
Gitweb:        https://git.kernel.org/tip/46a4ad7814fa39971aa6549b30c1a08d5c2ec65f
Author:        Masami Hiramatsu <mhiramat@xxxxxxxxxx>
AuthorDate:    Thu, 03 Dec 2020 13:51:01 +09:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 04 Dec 2020 14:45:15 +01:00

x86/sev-es: 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: 25189d08e516 ("x86/sev-es: Add support for handling IOIO exceptions")
Reported-by: syzbot+9b64b619f10f19d19a7c@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/160697106089.3146288.2052422845039649176.stgit@devnote2
---
 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 954cb27..27826c2 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;
 	}