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Date: Fri, 18 Jul 2014 10:47:49 +0900 From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Josh Poimboeuf <jpoimboe@...hat.com>, Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Ananth N Mavinakayanahalli <ananth@...ibm.com>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [PATCH ftrace/core v3 1/3] [BUGFIX]kprobes/ftrace: Recover original IP if pre_handler doesn't change it (2014/07/18 3:21), Steven Rostedt wrote: > This looks to require an acked-by from hpa. Oh, I see. > > On Tue, 15 Jul 2014 06:00:21 +0000 > Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote: > >> Recover original IP register if the pre_handler doesn't change it. >> Since current kprobes doesn't expect that another ftrace handler >> may change regs->ip, it sets kprobe.addr + MCOUNT_INSN_SIZE to >> regs->ip and returns to ftrace. >> This seems wrong behavior since kprobes can recover regs->ip >> and safely pass it to other handler. > > s/other/another/ > >> >> This adds a code which recovers original regs->ip passed from > > "... adds code which recovers the original ..." > >> ftrace right before returning ftrace, so that another ftrace user > > "... returning to ftrace, ..." Thanks, I'll update the description. :) > >> can change regs->ip. > > You say BUGFIX in the subject, but as nothing changes the regs->ip > currently from ftrace, is this currently a real bug? Hmm, indeed, in-tree ftrace handlers never change regs->ip except kprobes, and for the out-of-tree modules, we need IPMODIFY flag to avoid such conflict among them. Thus, we can not solve such problem only by this patch. OK, I'll drop BUGFIX tag. Thank you, > > -- Steve > >> >> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> >> --- >> arch/x86/kernel/kprobes/ftrace.c | 9 ++++++--- >> 1 file changed, 6 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c >> index 717b02a..5f8f0b3 100644 >> --- a/arch/x86/kernel/kprobes/ftrace.c >> +++ b/arch/x86/kernel/kprobes/ftrace.c >> @@ -27,7 +27,7 @@ >> >> static nokprobe_inline >> int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, >> - struct kprobe_ctlblk *kcb) >> + struct kprobe_ctlblk *kcb, unsigned long orig_ip) >> { >> /* >> * Emulate singlestep (and also recover regs->ip) >> @@ -39,6 +39,8 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, >> p->post_handler(p, regs, 0); >> } >> __this_cpu_write(current_kprobe, NULL); >> + if (orig_ip) >> + regs->ip = orig_ip; >> return 1; >> } >> >> @@ -46,7 +48,7 @@ int skip_singlestep(struct kprobe *p, struct pt_regs *regs, >> struct kprobe_ctlblk *kcb) >> { >> if (kprobe_ftrace(p)) >> - return __skip_singlestep(p, regs, kcb); >> + return __skip_singlestep(p, regs, kcb, 0); >> else >> return 0; >> } >> @@ -71,13 +73,14 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, >> if (kprobe_running()) { >> kprobes_inc_nmissed_count(p); >> } else { >> + unsigned long orig_ip = regs->ip; >> /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */ >> regs->ip = ip + sizeof(kprobe_opcode_t); >> >> __this_cpu_write(current_kprobe, p); >> kcb->kprobe_status = KPROBE_HIT_ACTIVE; >> if (!p->pre_handler || !p->pre_handler(p, regs)) >> - __skip_singlestep(p, regs, kcb); >> + __skip_singlestep(p, regs, kcb, orig_ip); >> /* >> * If pre_handler returns !0, it sets regs->ip and >> * resets current kprobe. >> > > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@...achi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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