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

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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@chromium.org>.

 [ bp: Massage commit message. ]

Fixes: 32d0b95300 ("x86/insn-eval: Add utility functions to get segment selector")
Reported-by: syzbot+9b64b619f10f19d19a7c@syzkaller.appspotmail.com
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/160697104969.3146288.16329307586428270032.stgit@devnote2
This commit is contained in:
Masami Hiramatsu 2020-12-03 13:50:50 +09:00 committed by Borislav Petkov
parent 4e9a5ae8df
commit 12cb908a11
1 changed files with 5 additions and 5 deletions
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10
arch/x86/lib/insn-eval.c
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@ -63,13 +63,12 @@ static bool is_string_insn(struct insn *insn)
*/ */
bool insn_has_rep_prefix(struct insn *insn) bool insn_has_rep_prefix(struct insn *insn)
{ {
insn_byte_t p;
int i; int i;
insn_get_prefixes(insn); insn_get_prefixes(insn);
for (i = 0; i < insn->prefixes.nbytes; i++) { for_each_insn_prefix(insn, i, p) {
insn_byte_t p = insn->prefixes.bytes[i];
if (p == 0xf2 || p == 0xf3) if (p == 0xf2 || p == 0xf3)
return true; return true;
} }
@ -95,14 +94,15 @@ static int get_seg_reg_override_idx(struct insn *insn)
{ {
int idx = INAT_SEG_REG_DEFAULT; int idx = INAT_SEG_REG_DEFAULT;
int num_overrides = 0, i; int num_overrides = 0, i;
insn_byte_t p;
insn_get_prefixes(insn); insn_get_prefixes(insn);
/* Look for any segment override prefixes. */ /* 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; insn_attr_t attr;
attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); attr = inat_get_opcode_attribute(p);
switch (attr) { switch (attr) {
case INAT_MAKE_PREFIX(INAT_PFX_CS): case INAT_MAKE_PREFIX(INAT_PFX_CS):
idx = INAT_SEG_REG_CS; idx = INAT_SEG_REG_CS;