Commit 2dd0e8d2 authored by Sandeepa Prabhu's avatar Sandeepa Prabhu Committed by Catalin Marinas
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arm64: Kprobes with single stepping support 



Add support for basic kernel probes(kprobes) and jump probes
(jprobes) for ARM64.

Kprobes utilizes software breakpoint and single step debug
exceptions supported on ARM v8.

A software breakpoint is placed at the probe address to trap the
kernel execution into the kprobe handler.

ARM v8 supports enabling single stepping before the break exception
return (ERET), with next PC in exception return address (ELR_EL1). The
kprobe handler prepares an executable memory slot for out-of-line
execution with a copy of the original instruction being probed, and
enables single stepping. The PC is set to the out-of-line slot address
before the ERET. With this scheme, the instruction is executed with the
exact same register context except for the PC (and DAIF) registers.

Debug mask (PSTATE.D) is enabled only when single stepping a recursive
kprobe, e.g.: during kprobes reenter so that probed instruction can be
single stepped within the kprobe handler -exception- context.
The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
any further re-entry is prevented by not calling handlers and the case
counted as a missed kprobe).

Single stepping from the x-o-l slot has a drawback for PC-relative accesses
like branching and symbolic literals access as the offset from the new PC
(slot address) may not be ensured to fit in the immediate value of
the opcode. Such instructions need simulation, so reject
probing them.

Instructions generating exceptions or cpu mode change are rejected
for probing.

Exclusive load/store instructions are rejected too.  Additionally, the
code is checked to see if it is inside an exclusive load/store sequence
(code from Pratyush).

System instructions are mostly enabled for stepping, except MSR/MRS
accesses to "DAIF" flags in PSTATE, which are not safe for
probing.

This also changes arch/arm64/include/asm/ptrace.h to use
include/asm-generic/ptrace.h.

Thanks to Steve Capper and Pratyush Anand for several suggested
Changes.

Signed-off-by: default avatarSandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
Signed-off-by: default avatarDavid A. Long <dave.long@linaro.org>
Signed-off-by: default avatarPratyush Anand <panand@redhat.com>
Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2af3ec08

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -88,6 +88,7 @@ config ARM64 
	select HAVE_REGS_AND_STACK_ACCESS_API

	select HAVE_RCU_TABLE_FREE

	select HAVE_SYSCALL_TRACEPOINTS

	select HAVE_KPROBES

	select IOMMU_DMA if IOMMU_SUPPORT

	select IRQ_DOMAIN

	select IRQ_FORCED_THREADING

arch/arm64/include/asm/debug-monitors.h

+5 −0
Original line number Diff line number Diff line
@@ -66,6 +66,11 @@ 


#define CACHE_FLUSH_IS_SAFE		1



/* kprobes BRK opcodes with ESR encoding  */

#define BRK64_ESR_MASK		0xFFFF

#define BRK64_ESR_KPROBES	0x0004

#define BRK64_OPCODE_KPROBES	(AARCH64_BREAK_MON | (BRK64_ESR_KPROBES << 5))



/* AArch32 */

#define DBG_ESR_EVT_BKPT	0x4

#define DBG_ESR_EVT_VECC	0x5

arch/arm64/include/asm/insn.h

+2 −0
Original line number Diff line number Diff line
@@ -253,6 +253,8 @@ __AARCH64_INSN_FUNCS(ldr_reg, 0x3FE0EC00, 0x38606800) 
__AARCH64_INSN_FUNCS(ldr_lit,	0xBF000000, 0x18000000)

__AARCH64_INSN_FUNCS(ldrsw_lit,	0xFF000000, 0x98000000)

__AARCH64_INSN_FUNCS(exclusive,	0x3F800000, 0x08000000)

__AARCH64_INSN_FUNCS(load_ex,	0x3F400000, 0x08400000)

__AARCH64_INSN_FUNCS(store_ex,	0x3F400000, 0x08000000)

__AARCH64_INSN_FUNCS(stp_post,	0x7FC00000, 0x28800000)

__AARCH64_INSN_FUNCS(ldp_post,	0x7FC00000, 0x28C00000)

__AARCH64_INSN_FUNCS(stp_pre,	0x7FC00000, 0x29800000)

arch/arm64/include/asm/kprobes.h

0 → 100644
+60 −0
Original line number Diff line number Diff line 
/*

 * arch/arm64/include/asm/kprobes.h

 *

 * Copyright (C) 2013 Linaro Limited

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * 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.

 */



#ifndef _ARM_KPROBES_H

#define _ARM_KPROBES_H



#include <linux/types.h>

#include <linux/ptrace.h>

#include <linux/percpu.h>



#define __ARCH_WANT_KPROBES_INSN_SLOT

#define MAX_INSN_SIZE			1

#define MAX_STACK_SIZE			128



#define flush_insn_slot(p)		do { } while (0)

#define kretprobe_blacklist_size	0



#include <asm/probes.h>



struct prev_kprobe {

	struct kprobe *kp;

	unsigned int status;

};



/* Single step context for kprobe */

struct kprobe_step_ctx {

	unsigned long ss_pending;

	unsigned long match_addr;

};



/* per-cpu kprobe control block */

struct kprobe_ctlblk {

	unsigned int kprobe_status;

	unsigned long saved_irqflag;

	struct prev_kprobe prev_kprobe;

	struct kprobe_step_ctx ss_ctx;

	struct pt_regs jprobe_saved_regs;

	char jprobes_stack[MAX_STACK_SIZE];

};



void arch_remove_kprobe(struct kprobe *);

int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);

int kprobe_exceptions_notify(struct notifier_block *self,

			     unsigned long val, void *data);

int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr);

int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr);



#endif /* _ARM_KPROBES_H */

arch/arm64/include/asm/probes.h

0 → 100644
+34 −0
Original line number Diff line number Diff line 
/*

 * arch/arm64/include/asm/probes.h

 *

 * Copyright (C) 2013 Linaro Limited

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * 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.

 */

#ifndef _ARM_PROBES_H

#define _ARM_PROBES_H



struct kprobe;

struct arch_specific_insn;



typedef u32 kprobe_opcode_t;

typedef unsigned long (kprobes_pstate_check_t)(unsigned long);

typedef void (kprobes_handler_t) (u32 opcode, long addr, struct pt_regs *);



/* architecture specific copy of original instruction */

struct arch_specific_insn {

	kprobe_opcode_t *insn;

	kprobes_pstate_check_t *pstate_cc;

	kprobes_handler_t *handler;

	/* restore address after step xol */

	unsigned long restore;

};



#endif

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