Commit ec6aba3d authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

kprobes: Remove kprobe::fault_handler 



The reason for kprobe::fault_handler(), as given by their comment:

 * We come here because instructions in the pre/post
 * handler caused the page_fault, this could happen
 * if handler tries to access user space by
 * copy_from_user(), get_user() etc. Let the
 * user-specified handler try to fix it first.

Is just plain bad. Those other handlers are ran from non-preemptible
context and had better use _nofault() functions. Also, there is no
upstream usage of this.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20210525073213.561116662@infradead.org
parent 9ce4d216

Documentation/trace/kprobes.rst

+5 −19
Original line number Diff line number Diff line
@@ -362,14 +362,11 @@ register_kprobe 
	#include <linux/kprobes.h>

	int register_kprobe(struct kprobe *kp);



Sets a breakpoint at the address kp->addr.  When the breakpoint is

hit, Kprobes calls kp->pre_handler.  After the probed instruction

is single-stepped, Kprobe calls kp->post_handler.  If a fault

occurs during execution of kp->pre_handler or kp->post_handler,

or during single-stepping of the probed instruction, Kprobes calls

kp->fault_handler.  Any or all handlers can be NULL. If kp->flags

is set KPROBE_FLAG_DISABLED, that kp will be registered but disabled,

so, its handlers aren't hit until calling enable_kprobe(kp).

Sets a breakpoint at the address kp->addr.  When the breakpoint is hit, Kprobes

calls kp->pre_handler.  After the probed instruction is single-stepped, Kprobe

calls kp->post_handler.  Any or all handlers can be NULL. If kp->flags is set

KPROBE_FLAG_DISABLED, that kp will be registered but disabled, so, its handlers

aren't hit until calling enable_kprobe(kp).



.. note::
@@ -415,17 +412,6 @@ User's post-handler (kp->post_handler):: 
p and regs are as described for the pre_handler.  flags always seems

to be zero.



User's fault-handler (kp->fault_handler)::



	#include <linux/kprobes.h>

	#include <linux/ptrace.h>

	int fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr);



p and regs are as described for the pre_handler.  trapnr is the

architecture-specific trap number associated with the fault (e.g.,

on i386, 13 for a general protection fault or 14 for a page fault).

Returns 1 if it successfully handled the exception.



register_kretprobe

------------------

arch/arc/kernel/kprobes.c

+0 −10
Original line number Diff line number Diff line
@@ -323,16 +323,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned long trapnr) 
		 */

		kprobes_inc_nmissed_count(cur);



		/*

		 * We come here because instructions in the pre/post

		 * handler caused the page_fault, this could happen

		 * if handler tries to access user space by

		 * copy_from_user(), get_user() etc. Let the

		 * user-specified handler try to fix it first.

		 */

		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))

			return 1;



		/*

		 * In case the user-specified fault handler returned zero,

		 * try to fix up.

arch/arm/probes/kprobes/core.c

+0 −9
Original line number Diff line number Diff line
@@ -358,15 +358,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) 
		 */

		kprobes_inc_nmissed_count(cur);



		/*

		 * We come here because instructions in the pre/post

		 * handler caused the page_fault, this could happen

		 * if handler tries to access user space by

		 * copy_from_user(), get_user() etc. Let the

		 * user-specified handler try to fix it.

		 */

		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))

			return 1;

		break;



	default:

arch/arm64/kernel/probes/kprobes.c

+0 −10
Original line number Diff line number Diff line
@@ -283,16 +283,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) 
		 */

		kprobes_inc_nmissed_count(cur);



		/*

		 * We come here because instructions in the pre/post

		 * handler caused the page_fault, this could happen

		 * if handler tries to access user space by

		 * copy_from_user(), get_user() etc. Let the

		 * user-specified handler try to fix it first.

		 */

		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))

			return 1;



		/*

		 * In case the user-specified fault handler returned

		 * zero, try to fix up.

arch/csky/kernel/probes/kprobes.c

+0 −10
Original line number Diff line number Diff line
@@ -301,16 +301,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr) 
		 */

		kprobes_inc_nmissed_count(cur);



		/*

		 * We come here because instructions in the pre/post

		 * handler caused the page_fault, this could happen

		 * if handler tries to access user space by

		 * copy_from_user(), get_user() etc. Let the

		 * user-specified handler try to fix it first.

		 */

		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))

			return 1;



		/*

		 * In case the user-specified fault handler returned

		 * zero, try to fix up.