[PATCH v3 3/3] x86/sev-es: Fix not using prefixes.nbytes for loop over prefixes.bytes

[Masami Hiramatsu]

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+9b64b619f10f19d19...@syzkaller.appspotmail.com
Debugged-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Masami Hiramatsu <mhira...@kernel.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;
        }