From cefa72129e45313655d53a065b8055aaeb01a0c9 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Sun, 4 Dec 2022 18:39:33 +0100 Subject: [PATCH] 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: 250bbd12c2fe ("uprobes/x86: Refuse to attach uprobe to "word-sized" branch insns") Reported-by: Seiji Nishikawa Suggested-by: Denys Vlasenko Signed-off-by: Oleg Nesterov Signed-off-by: Thomas Gleixner Acked-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/r/20221204173933.GA31544@redhat.com --- arch/x86/kernel/uprobes.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index b63cf8f..6c07f6d 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -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; -- 2.7.4