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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20210525073213.561116662@infradead.org
This commit is contained in:
Peter Zijlstra 2021-05-25 09:25:19 +02:00
parent 9ce4d216fe
commit ec6aba3d2b
16 changed files with 5 additions and 172 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
Documentation/trace/kprobes.rst
View File

@ -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
------------------

10
arch/arc/kernel/kprobes.c
View File

@ -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.

9
arch/arm/probes/kprobes/core.c
View File

@ -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:

10
arch/arm64/kernel/probes/kprobes.c
View File

@ -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.

10
arch/csky/kernel/probes/kprobes.c
View File

@ -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.

9
arch/ia64/kernel/kprobes.c
View File

@ -850,15 +850,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, 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.

3
arch/mips/kernel/kprobes.c
View File

@ -403,9 +403,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
struct kprobe *cur = kprobe_running();
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
return 1;
if (kcb->kprobe_status & KPROBE_HIT_SS) {
resume_execution(cur, regs, kcb);
regs->cp0_status |= kcb->kprobe_old_SR;

10
arch/powerpc/kernel/kprobes.c
View File

@ -508,16 +508,6 @@ int kprobe_fault_handler(struct pt_regs *regs, 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.

10
arch/riscv/kernel/probes/kprobes.c
View File

@ -283,16 +283,6 @@ 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.

10
arch/s390/kernel/kprobes.c
View File

@ -452,16 +452,6 @@ static int kprobe_trap_handler(struct pt_regs *regs, int trapnr)
*/
kprobes_inc_nmissed_count(p);
/*
* 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 (p->fault_handler && p->fault_handler(p, regs, trapnr))
return 1;
/*
* In case the user-specified fault handler returned
* zero, try to fix up.

10
arch/sh/kernel/kprobes.c
View File

@ -389,16 +389,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, 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.

10
arch/sparc/kernel/kprobes.c
View File

@ -352,16 +352,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, 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.

10
arch/x86/kernel/kprobes/core.c
View File

@ -1110,16 +1110,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
* these specific fault cases.
*/
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;
}
return 0;

8
include/linux/kprobes.h
View File

@ -54,8 +54,6 @@ struct kretprobe_instance;
typedef int (*kprobe_pre_handler_t) (struct kprobe *, struct pt_regs *);
typedef void (*kprobe_post_handler_t) (struct kprobe *, struct pt_regs *,
unsigned long flags);
typedef int (*kprobe_fault_handler_t) (struct kprobe *, struct pt_regs *,
int trapnr);
typedef int (*kretprobe_handler_t) (struct kretprobe_instance *,
struct pt_regs *);
@ -83,12 +81,6 @@ struct kprobe {
/* Called after addr is executed, unless... */
kprobe_post_handler_t post_handler;
/*
* ... called if executing addr causes a fault (eg. page fault).
* Return 1 if it handled fault, otherwise kernel will see it.
*/
kprobe_fault_handler_t fault_handler;
/* Saved opcode (which has been replaced with breakpoint) */
kprobe_opcode_t opcode;

19
kernel/kprobes.c
View File

@ -1183,23 +1183,6 @@ static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
}
NOKPROBE_SYMBOL(aggr_post_handler);
static int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
int trapnr)
{
struct kprobe *cur = __this_cpu_read(kprobe_instance);
/*
* if we faulted "during" the execution of a user specified
* probe handler, invoke just that probe's fault handler
*/
if (cur && cur->fault_handler) {
if (cur->fault_handler(cur, regs, trapnr))
return 1;
}
return 0;
}
NOKPROBE_SYMBOL(aggr_fault_handler);
/* Walks the list and increments nmissed count for multiprobe case */
void kprobes_inc_nmissed_count(struct kprobe *p)
{
@ -1330,7 +1313,6 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
ap->addr = p->addr;
ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;
ap->pre_handler = aggr_pre_handler;
ap->fault_handler = aggr_fault_handler;
/* We don't care the kprobe which has gone. */
if (p->post_handler && !kprobe_gone(p))
ap->post_handler = aggr_post_handler;
@ -2014,7 +1996,6 @@ int register_kretprobe(struct kretprobe *rp)
rp->kp.pre_handler = pre_handler_kretprobe;
rp->kp.post_handler = NULL;
rp->kp.fault_handler = NULL;
/* Pre-allocate memory for max kretprobe instances */
if (rp->maxactive <= 0) {

15
samples/kprobes/kprobe_example.c
View File

@ -94,26 +94,11 @@ static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
#endif
}
/*
* fault_handler: this is called if an exception is generated for any
* instruction within the pre- or post-handler, or when Kprobes
* single-steps the probed instruction.
*/
static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
{
pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr);
/* Return 0 because we don't handle the fault. */
return 0;
}
/* NOKPROBE_SYMBOL() is also available */
NOKPROBE_SYMBOL(handler_fault);
static int __init kprobe_init(void)
{
int ret;
kp.pre_handler = handler_pre;
kp.post_handler = handler_post;
kp.fault_handler = handler_fault;
ret = register_kprobe(&kp);
if (ret < 0) {