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uprobes/x86: Allow to probe a NOP instruction with 0x66 prefix 

Intel ICC -hotpatch inserts 2-byte "0x66 0x90" NOP at the start of each
function to reserve extra space for hot-patching, and currently it is not
possible to probe these functions because branch_setup_xol_ops() wrongly
rejects NOP with REP prefix as it treats them like word-sized branch
instructions.

Fixes: 250bbd12c2 ("uprobes/x86: Refuse to attach uprobe to "word-sized" branch insns")
Reported-by: Seiji Nishikawa <snishika@redhat.com>
Suggested-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20221204173933.GA31544@redhat.com
This commit is contained in:
Oleg Nesterov 2022-12-04 18:39:33 +01:00 committed by Thomas Gleixner
parent 023e59d4ce
commit cefa72129e
1 changed files with 3 additions and 1 deletions
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4
arch/x86/kernel/uprobes.c
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@ -722,8 +722,9 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
switch (opc1) {
case 0xeb: /* jmp 8 */
case 0xe9: /* jmp 32 */
case 0x90: /* prefix* + nop; same as jmp with .offs = 0 */
break;
case 0x90: /* prefix* + nop; same as jmp with .offs = 0 */
goto setup;
case 0xe8: /* call relative */
branch_clear_offset(auprobe, insn);
@ -753,6 +754,7 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
return -ENOTSUPP;
}
setup:
auprobe->branch.opc1 = opc1;
auprobe->branch.ilen = insn->length;
auprobe->branch.offs = insn->immediate.value;