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Commit 9a556ab9 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Ingo Molnar
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kprobes/x86: Check Interrupt Flag modifier when registering probe 



Currently kprobes check whether the copied instruction modifies
IF (interrupt flag) on each probe hit. This results not only in
introducing overhead but also involving
inat_get_opcode_attribute into the kprobes hot path, and it can
cause an infinite recursive call (and kernel panic in the end).

Actually, since the copied instruction itself can never be modified
on the buffer, it is needless to analyze the instruction on every
probe hit.

To fix this issue, we check it only once when registering probe
and store the result on ainsn->if_modifier.

Reported-by: default avatarTimo Juhani Lindfors <timo.lindfors@iki.fi>
Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: yrl.pp-manager.tt@hitachi.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20130314115242.19690.33573.stgit@mhiramat-M0-7522


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 65c10553

arch/x86/include/asm/kprobes.h

+1 −0
Original line number Diff line number Diff line
@@ -77,6 +77,7 @@ struct arch_specific_insn { 
	 * a post_handler or break_handler).

	 */

	int boostable;

	bool if_modifier;

};



struct arch_optimized_insn {

arch/x86/kernel/kprobes/core.c

+4 −1
Original line number Diff line number Diff line
@@ -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;

}