Currently kprobes check whether the copied instruction modifies IF (interrupt flag) on each probe hit. This means not only introducing overhead but also involving inat_get_opcode_attribute into kprobes hot path, and it can cause an infinit recursive call (and kernel panic in the end).
Actually, since the copied instruction itself never be modified on the buffer, it is needless to analyze the instruction every probe hit. To fix this issue, we checks it only once when registering probe and store the result on ainsn->if_modifier. Signed-off-by: Masami Hiramatsu <[email protected]> Reported-by: Timo Juhani Lindfors <[email protected]> Cc: "David S. Miller" <[email protected]> Cc: Ananth N Mavinakayanahalli <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Linus Torvalds <[email protected]> --- arch/x86/include/asm/kprobes.h | 1 + arch/x86/kernel/kprobes/core.c | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h index d3ddd17..5a6d287 100644 --- a/arch/x86/include/asm/kprobes.h +++ b/arch/x86/include/asm/kprobes.h @@ -77,6 +77,7 @@ struct arch_specific_insn { * a post_handler or break_handler). */ int boostable; + bool if_modifier; }; struct arch_optimized_insn { diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index 3f06e61..7bfe318 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -375,6 +375,9 @@ static void __kprobes arch_copy_kprobe(struct kprobe *p) else p->ainsn.boostable = -1; + /* Check whether the instruction modifies Interrupt Flag or not */ + p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn); + /* Also, displacement change doesn't affect the first byte */ p->opcode = p->ainsn.insn[0]; } @@ -434,7 +437,7 @@ static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs, __this_cpu_write(current_kprobe, p); kcb->kprobe_saved_flags = kcb->kprobe_old_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF)); - if (is_IF_modifier(p->ainsn.insn)) + if (p->ainsn.if_modifier) kcb->kprobe_saved_flags &= ~X86_EFLAGS_IF; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
