Commit 3f92dfed authored by Jon Medhurst's avatar Jon Medhurst Committed by Tixy
Browse files

ARM: kprobes: Decode 16-bit Thumb hint instructions 



For hints which may have observable effects, like SEV (send event), we
use kprobe_emulate_none which emulates the hint by executing the
original instruction.

For NOP we simulate the instruction using kprobe_simulate_nop, which
does nothing. As probes execute with interrupts disabled this is also
used for hints which may block for an indefinite time, like WFE (wait
for event).

Signed-off-by: default avatarJon Medhurst <tixy@yxit.co.uk>
Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
parent 0d1a095a

arch/arm/kernel/kprobes-common.c

+9 −0
Original line number Diff line number Diff line
@@ -142,6 +142,15 @@ kprobe_check_cc * const kprobe_condition_checks[16] = { 
};





void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs)

{

}



void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs)

{

	p->ainsn.insn_fn();

}



/*

 * Prepare an instruction slot to receive an instruction for emulating.

 * This is done by placing a subroutine return after the location where the

arch/arm/kernel/kprobes-thumb.c

+34 −1
Original line number Diff line number Diff line
@@ -26,6 +26,39 @@ 
 */

#define current_cond(cpsr)	((cpsr >> 12) & 0xf)



static const union decode_item t16_table_1011[] = {

	/* Miscellaneous 16-bit instructions		    */



	/*

	 * If-Then, and hints

	 *				1011 1111 xxxx xxxx

	 */



	/* YIELD			1011 1111 0001 0000 */

	DECODE_OR	(0xffff, 0xbf10),

	/* SEV				1011 1111 0100 0000 */

	DECODE_EMULATE	(0xffff, 0xbf40, kprobe_emulate_none),

	/* NOP				1011 1111 0000 0000 */

	/* WFE				1011 1111 0010 0000 */

	/* WFI				1011 1111 0011 0000 */

	DECODE_SIMULATE	(0xffcf, 0xbf00, kprobe_simulate_nop),

	/* Unassigned hints		1011 1111 xxxx 0000 */

	DECODE_REJECT	(0xff0f, 0xbf00),



	DECODE_END

};



const union decode_item kprobe_decode_thumb16_table[] = {



	/*

	 * Miscellaneous 16-bit instructions

	 *				1011 xxxx xxxx xxxx

	 */

	DECODE_TABLE	(0xf000, 0xb000, t16_table_1011),



	DECODE_END

};



static unsigned long __kprobes thumb_check_cc(unsigned long cpsr)

{

	if (unlikely(in_it_block(cpsr)))
@@ -52,7 +85,7 @@ thumb16_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi) 
{

	asi->insn_singlestep = thumb16_singlestep;

	asi->insn_check_cc = thumb_check_cc;

	return INSN_REJECTED;

	return kprobe_decode_insn(insn, asi, kprobe_decode_thumb16_table, true);

}



enum kprobe_insn __kprobes

arch/arm/kernel/kprobes.h

+3 −0
Original line number Diff line number Diff line
@@ -95,6 +95,9 @@ static inline unsigned long it_advance(unsigned long cpsr) 
	return cpsr;

}



void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs);

void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs);



/*

 * Test if load/store instructions writeback the address register.

 * if P (bit 24) == 0 or W (bit 21) == 1

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