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    SubjectRe: [tip:perf/kprobes] kprobes/x86: Call exception handlers directly from do_int3/do_debug
    On Thu, 24 Apr 2014, tip-bot for Masami Hiramatsu wrote:

    > Commit-ID: 6f6343f53d133bae516caf3d254bce37d8774625
    > Gitweb: http://git.kernel.org/tip/6f6343f53d133bae516caf3d254bce37d8774625
    > Author: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    > AuthorDate: Thu, 17 Apr 2014 17:17:33 +0900
    > Committer: Ingo Molnar <mingo@kernel.org>
    > CommitDate: Thu, 24 Apr 2014 10:02:59 +0200
    >
    > kprobes/x86: Call exception handlers directly from do_int3/do_debug
    >
    > To avoid a kernel crash by probing on lockdep code, call
    > kprobe_int3_handler() and kprobe_debug_handler()(which was
    > formerly called post_kprobe_handler()) directly from
    > do_int3 and do_debug.
    >
    > Currently kprobes uses notify_die() to hook the int3/debug
    > exceptoins. Since there is a locking code in notify_die,
    > the lockdep code can be invoked. And because the lockdep
    > involves printk() related things, theoretically, we need to
    > prohibit probing on such code, which means much longer blacklist
    > we'll have. Instead, hooking the int3/debug for kprobes before
    > notify_die() can avoid this problem.
    >
    > Anyway, most of the int3 handlers in the kernel are already
    > called from do_int3 directly, e.g. ftrace_int3_handler,
    > poke_int3_handler, kgdb_ll_trap. Actually only
    > kprobe_exceptions_notify is on the notifier_call_chain.
    >
    > 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>

    Reviewed-by: Jiri Kosina <jkosina@suse.cz>

    > Cc: Jonathan Lebon <jlebon@redhat.com>
    > 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/20140417081733.26341.24423.stgit@ltc230.yrl.intra.hitachi.co.jp
    > Signed-off-by: Ingo Molnar <mingo@kernel.org>
    > ---
    > arch/x86/include/asm/kprobes.h | 2 ++
    > arch/x86/kernel/kprobes/core.c | 24 +++---------------------
    > arch/x86/kernel/traps.c | 10 ++++++++++
    > 3 files changed, 15 insertions(+), 21 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
    > index 9454c16..53cdfb2 100644
    > --- a/arch/x86/include/asm/kprobes.h
    > +++ b/arch/x86/include/asm/kprobes.h
    > @@ -116,4 +116,6 @@ struct kprobe_ctlblk {
    > extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
    > extern int kprobe_exceptions_notify(struct notifier_block *self,
    > unsigned long val, void *data);
    > +extern int kprobe_int3_handler(struct pt_regs *regs);
    > +extern int kprobe_debug_handler(struct pt_regs *regs);
    > #endif /* _ASM_X86_KPROBES_H */
    > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
    > index 7751b3d..9b80aec 100644
    > --- a/arch/x86/kernel/kprobes/core.c
    > +++ b/arch/x86/kernel/kprobes/core.c
    > @@ -559,7 +559,7 @@ reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb
    > * Interrupts are disabled on entry as trap3 is an interrupt gate and they
    > * remain disabled throughout this function.
    > */
    > -static int __kprobes kprobe_handler(struct pt_regs *regs)
    > +int __kprobes kprobe_int3_handler(struct pt_regs *regs)
    > {
    > kprobe_opcode_t *addr;
    > struct kprobe *p;
    > @@ -857,7 +857,7 @@ no_change:
    > * Interrupts are disabled on entry as trap1 is an interrupt gate and they
    > * remain disabled throughout this function.
    > */
    > -static int __kprobes post_kprobe_handler(struct pt_regs *regs)
    > +int __kprobes kprobe_debug_handler(struct pt_regs *regs)
    > {
    > struct kprobe *cur = kprobe_running();
    > struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    > @@ -963,22 +963,7 @@ kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *d
    > if (args->regs && user_mode_vm(args->regs))
    > return ret;
    >
    > - switch (val) {
    > - case DIE_INT3:
    > - if (kprobe_handler(args->regs))
    > - ret = NOTIFY_STOP;
    > - break;
    > - case DIE_DEBUG:
    > - if (post_kprobe_handler(args->regs)) {
    > - /*
    > - * Reset the BS bit in dr6 (pointed by args->err) to
    > - * denote completion of processing
    > - */
    > - (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
    > - ret = NOTIFY_STOP;
    > - }
    > - break;
    > - case DIE_GPF:
    > + if (val == DIE_GPF) {
    > /*
    > * To be potentially processing a kprobe fault and to
    > * trust the result from kprobe_running(), we have
    > @@ -987,9 +972,6 @@ kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *d
    > if (!preemptible() && kprobe_running() &&
    > kprobe_fault_handler(args->regs, args->trapnr))
    > ret = NOTIFY_STOP;
    > - break;
    > - default:
    > - break;
    > }
    > return ret;
    > }
    > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
    > index 57409f6..e5d4a70 100644
    > --- a/arch/x86/kernel/traps.c
    > +++ b/arch/x86/kernel/traps.c
    > @@ -334,6 +334,11 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co
    > goto exit;
    > #endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
    >
    > +#ifdef CONFIG_KPROBES
    > + if (kprobe_int3_handler(regs))
    > + return;
    > +#endif
    > +
    > if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
    > SIGTRAP) == NOTIFY_STOP)
    > goto exit;
    > @@ -440,6 +445,11 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
    > /* Store the virtualized DR6 value */
    > tsk->thread.debugreg6 = dr6;
    >
    > +#ifdef CONFIG_KPROBES
    > + if (kprobe_debug_handler(regs))
    > + goto exit;
    > +#endif
    > +
    > if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
    > SIGTRAP) == NOTIFY_STOP)
    > goto exit;
    >

    --
    Jiri Kosina
    SUSE Labs


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