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SubjectRe: [PATCH -tip v8 08/26] kprobes/x86: Call exception handlers directly from do_int3/do_debug
On Wed, 05 Mar 2014 20:59:39 +0900
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:

> To avoid a kernel crash by probing on lockdep code, call
> kprobe_int3_handler and kprobe_debug_handler directly
> from do_int3 and do_debug. Since there is a locking code
> in notify_die, lockdep code can be invoked. And because
> the lockdep involves printk() related things, theoretically,
> we need to prohibit probing on much more code...
>
> 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>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Seiji Aguchi <seiji.aguchi@hds.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> 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 4708d6e..566958e 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();
> @@ -960,22 +960,7 @@ 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;
> - }

The DIE_DEBUG case is removed but not added anyplace else. The change
log doesn't say why this was removed.

-- Steve

> - 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
> @@ -984,9 +969,6 @@ 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;
>



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