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powerpc/kprobes: Add support for KPROBES_ON_FTRACE

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Allow kprobes to be placed on ftrace _mcount() call sites. This optimization
avoids the use of a trap, by riding on ftrace infrastructure.

This depends on HAVE_DYNAMIC_FTRACE_WITH_REGS which depends on MPROFILE_KERNEL,
which is only currently enabled on powerpc64le with newer toolchains.

Based on the x86 code by Masami.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2017-04-19 18:22:26 +05:30 committed by Michael Ellerman
parent 2f59be5b97
commit ead514d5fb
6 changed files with 126 additions and 2 deletions
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2
Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
View File

@ -27,7 +27,7 @@
| nios2: | TODO |
| openrisc: | TODO |
| parisc: | TODO |
| powerpc: | TODO |
| powerpc: | ok |
| s390: | TODO |
| score: | TODO |
| sh: | TODO |

1
arch/powerpc/Kconfig
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@ -142,6 +142,7 @@ config PPC
select HAVE_IRQ_EXIT_ON_IRQ_STACK
select HAVE_KERNEL_GZIP
select HAVE_KPROBES
select HAVE_KPROBES_ON_FTRACE
select HAVE_KRETPROBES
select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS
select HAVE_MEMBLOCK

10
arch/powerpc/include/asm/kprobes.h
View File

@ -103,6 +103,16 @@ extern int kprobe_exceptions_notify(struct notifier_block *self,
extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
extern int kprobe_handler(struct pt_regs *regs);
extern int kprobe_post_handler(struct pt_regs *regs);
#ifdef CONFIG_KPROBES_ON_FTRACE
extern int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb);
#else
static inline int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb)
{
return 0;
}
#endif
#else
static inline int kprobe_handler(struct pt_regs *regs) { return 0; }
static inline int kprobe_post_handler(struct pt_regs *regs) { return 0; }

3
arch/powerpc/kernel/Makefile
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@ -97,6 +97,7 @@ obj-$(CONFIG_BOOTX_TEXT) += btext.o
obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_KPROBES) += kprobes.o
obj-$(CONFIG_OPTPROBES) += optprobes.o optprobes_head.o
obj-$(CONFIG_KPROBES_ON_FTRACE) += kprobes-ftrace.o
obj-$(CONFIG_UPROBES) += uprobes.o
obj-$(CONFIG_PPC_UDBG_16550) += legacy_serial.o udbg_16550.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
@ -150,6 +151,8 @@ GCOV_PROFILE_machine_kexec_32.o := n
UBSAN_SANITIZE_machine_kexec_32.o := n
GCOV_PROFILE_kprobes.o := n
UBSAN_SANITIZE_kprobes.o := n
GCOV_PROFILE_kprobes-ftrace.o := n
UBSAN_SANITIZE_kprobes-ftrace.o := n
UBSAN_SANITIZE_vdso.o := n
extra-$(CONFIG_PPC_FPU) += fpu.o

104
arch/powerpc/kernel/kprobes-ftrace.c Normal file
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@ -0,0 +1,104 @@
/*
* Dynamic Ftrace based Kprobes Optimization
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) Hitachi Ltd., 2012
* Copyright 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
* IBM Corporation
*/
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/hardirq.h>
#include <linux/preempt.h>
#include <linux/ftrace.h>
static nokprobe_inline
int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb, unsigned long orig_nip)
{
/*
* Emulate singlestep (and also recover regs->nip)
* as if there is a nop
*/
regs->nip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;
if (unlikely(p->post_handler)) {
kcb->kprobe_status = KPROBE_HIT_SSDONE;
p->post_handler(p, regs, 0);
}
__this_cpu_write(current_kprobe, NULL);
if (orig_nip)
regs->nip = orig_nip;
return 1;
}
int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb)
{
if (kprobe_ftrace(p))
return __skip_singlestep(p, regs, kcb, 0);
else
return 0;
}
NOKPROBE_SYMBOL(skip_singlestep);
/* Ftrace callback handler for kprobes */
void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
struct ftrace_ops *ops, struct pt_regs *regs)
{
struct kprobe *p;
struct kprobe_ctlblk *kcb;
unsigned long flags;
/* Disable irq for emulating a breakpoint and avoiding preempt */
local_irq_save(flags);
hard_irq_disable();
p = get_kprobe((kprobe_opcode_t *)nip);
if (unlikely(!p) || kprobe_disabled(p))
goto end;
kcb = get_kprobe_ctlblk();
if (kprobe_running()) {
kprobes_inc_nmissed_count(p);
} else {
unsigned long orig_nip = regs->nip;
/*
* On powerpc, NIP is *before* this instruction for the
* pre handler
*/
regs->nip -= MCOUNT_INSN_SIZE;
__this_cpu_write(current_kprobe, p);
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
if (!p->pre_handler || !p->pre_handler(p, regs))
__skip_singlestep(p, regs, kcb, orig_nip);
/*
* If pre_handler returns !0, it sets regs->nip and
* resets current kprobe.
*/
}
end:
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
p->ainsn.insn = NULL;
p->ainsn.boostable = -1;
return 0;
}

8
arch/powerpc/kernel/kprobes.c
View File

@ -192,7 +192,11 @@ static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
bool arch_function_offset_within_entry(unsigned long offset)
{
#ifdef PPC64_ELF_ABI_v2
#ifdef CONFIG_KPROBES_ON_FTRACE
return offset <= 16;
#else
return offset <= 8;
#endif
#else
return !offset;
#endif
@ -301,7 +305,9 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
}
p = __this_cpu_read(current_kprobe);
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;
if (!skip_singlestep(p, regs, kcb))
goto ss_probe;
ret = 1;
}
}
goto no_kprobe;