Hi Frederic, (2014/06/14 2:14), Frederic Weisbecker wrote: > Hi Masami, > > 2014-04-24 12:59 GMT+02:00 tip-bot for Masami Hiramatsu <tipbot@xxxxxxxxx>: >> Commit-ID: ecd50f714c421c759354632dd00f70c718c95b10 >> Gitweb: http://git.kernel.org/tip/ecd50f714c421c759354632dd00f70c718c95b10 >> Author: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> >> AuthorDate: Thu, 17 Apr 2014 17:17:40 +0900 >> Committer: Ingo Molnar <mingo@xxxxxxxxxx> >> 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@xxxxxxxxxxx> >> Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: Borislav Petkov <bp@xxxxxxx> >> Cc: Jiri Kosina <jkosina@xxxxxxx> >> Cc: Kees Cook <keescook@xxxxxxxxxxxx> >> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> >> Cc: Seiji Aguchi <seiji.aguchi@xxxxxxx> >> Link: http://lkml.kernel.org/r/20140417081740.26341.10894.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx >> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > > 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; Oops, obviously there are bugs... > 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_andle() use RCU read side critical sections? I'm also > worried about kmemcheck... As far as I can check the code again, it is enough to remove this patch and to add context_track_user_*() to kprobe blacklist, since those checks in_interrupt() at the entry and returns immediately. It seems we have no problem on it. I think that was my fault. :( I'll send a bugfix, thank you! > >> --- >> 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@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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