Messages in this thread Patch in this message | | | Date | Fri, 13 Jun 2014 19:14:02 +0200 | Subject | Re: [tip:perf/kprobes] kprobes, x86: Call exception_enter after kprobes handled | From | Frederic Weisbecker <> |
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Hi Masami,
2014-04-24 12:59 GMT+02:00 tip-bot for Masami Hiramatsu <tipbot@zytor.com>: > Commit-ID: ecd50f714c421c759354632dd00f70c718c95b10 > Gitweb: http://git.kernel.org/tip/ecd50f714c421c759354632dd00f70c718c95b10 > Author: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> > AuthorDate: Thu, 17 Apr 2014 17:17:40 +0900 > Committer: Ingo Molnar <mingo@kernel.org> > CommitDate: Thu, 24 Apr 2014 10:03:00 +0200 > > kprobes, x86: Call exception_enter after kprobes handled > > Move exception_enter() call after kprobes handler > is done. Since the exception_enter() involves > many other functions (like printk), it can cause > recursive int3/break loop when kprobes probe such > functions. > > Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> > Reviewed-by: Steven Rostedt <rostedt@goodmis.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Borislav Petkov <bp@suse.de> > Cc: Jiri Kosina <jkosina@suse.cz> > Cc: Kees Cook <keescook@chromium.org> > Cc: Rusty Russell <rusty@rustcorp.com.au> > Cc: Seiji Aguchi <seiji.aguchi@hds.com> > Link: http://lkml.kernel.org/r/20140417081740.26341.10894.stgit@ltc230.yrl.intra.hitachi.co.jp > Signed-off-by: Ingo Molnar <mingo@kernel.org>
This patch results in exception_enter/exception_exit imbalances:
arch/x86/kernel/traps.c: In function ‘do_debug’: include/linux/context_tracking.h:46:6: warning: ‘prev_state’ may be used uninitialized in this function [-Wmaybe-uninitialized] if (prev_ctx == IN_USER) ^ arch/x86/kernel/traps.c:431:17: note: ‘prev_state’ was declared here enum ctx_state prev_state;
An obvious solution would be to change all the goto exit before exception_enter() to return from do_debug(). But if there are any user of RCU before exception_enter() this won't work. Does kprobe_debug_handle() use RCU read side critical sections? I'm also worried about kmemcheck...
> --- > arch/x86/kernel/traps.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e5d4a70..ba9abe9 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -327,7 +327,6 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co > if (poke_int3_handler(regs)) > return; > > - prev_state = exception_enter(); > #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP > if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, > SIGTRAP) == NOTIFY_STOP) > @@ -338,6 +337,7 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co > if (kprobe_int3_handler(regs)) > return; > #endif > + prev_state = exception_enter(); > > if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, > SIGTRAP) == NOTIFY_STOP) > @@ -415,8 +415,6 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > unsigned long dr6; > int si_code; > > - prev_state = exception_enter(); > - > get_debugreg(dr6, 6); > > /* Filter out all the reserved bits which are preset to 1 */ > @@ -449,6 +447,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > if (kprobe_debug_handler(regs)) > goto exit; > #endif > + prev_state = exception_enter(); > > if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code, > SIGTRAP) == NOTIFY_STOP) > -- > To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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