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Commit ead514d5 authored by Naveen N. Rao's avatar Naveen N. Rao Committed by Michael Ellerman
Browse files

powerpc/kprobes: Add support for KPROBES_ON_FTRACE 



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: default avatarNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 2f59be5b

Documentation/features/debug/kprobes-on-ftrace/arch-support.txt

+1 −1
Original line number Diff line number Diff line
@@ -27,7 +27,7 @@ 
    |       nios2: | TODO |

    |    openrisc: | TODO |

    |      parisc: | TODO |

    |     powerpc: | TODO |

    |     powerpc: |  ok  |

    |        s390: | TODO |

    |       score: | TODO |

    |          sh: | TODO |

arch/powerpc/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/include/asm/kprobes.h

+10 −0
Original line number Diff line number Diff line
@@ -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; }

arch/powerpc/kernel/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/kernel/kprobes-ftrace.c

0 → 100644
+104 −0
Original line number Diff line number Diff line 
/*

 * 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;

}