Commit 12cb908a authored Dec 03, 2020 by Masami Hiramatsu Committed by Borislav Petkov Dec 06, 2020

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@chromium.org>.

 [ bp: Massage commit message. ]

Fixes: 32d0b953 ("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

parent 4e9a5ae8

arch/x86/lib/insn-eval.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -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;

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