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Commit 3b7d14e9 authored by Marc Zyngier's avatar Marc Zyngier Committed by Catalin Marinas
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arm64: kprobes: Cleanup jprobe_return 



jprobe_return seems to have aged badly. Comments referring to
non-existent behaviours, and a dangerous habit of messing
with registers without telling the compiler.

This patches applies the following remedies:
- Fix the comments to describe the actual behaviour
- Tidy up the asm sequence to directly assign the
  stack pointer without clobbering extra registers
- Mark the rest of the function as unreachable() so
  that the compiler knows that there is no need for
  an epilogue
- Stop making jprobe_return_break a global function
  (you really don't want to call that guy, and it isn't
  even a function).

Tested with tcp_probe.

Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent ab4c1325

arch/arm64/kernel/probes/kprobes.c

+10 −12
Original line number Diff line number Diff line
@@ -34,8 +34,6 @@ 


#include "decode-insn.h"



void jprobe_return_break(void);



DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;

DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
@@ -516,18 +514,17 @@ void __kprobes jprobe_return(void) 
	/*

	 * Jprobe handler return by entering break exception,

	 * encoded same as kprobe, but with following conditions

	 * -a magic number in x0 to identify from rest of other kprobes.

	 * -a special PC to identify it from the other kprobes.

	 * -restore stack addr to original saved pt_regs

	 */

	asm volatile ("ldr x0, [%0]\n\t"

		      "mov sp, x0\n\t"

		      ".globl jprobe_return_break\n\t"

		      "jprobe_return_break:\n\t"

		      "brk %1\n\t"

	asm volatile("				mov sp, %0	\n"

		     "jprobe_return_break:	brk %1		\n"

		     :

		      : "r"(&kcb->jprobe_saved_regs.sp),

		     : "r" (kcb->jprobe_saved_regs.sp),

		       "I" (BRK64_ESR_KPROBES)

		     : "memory");



	unreachable();

}



int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
@@ -536,6 +533,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) 
	long stack_addr = kcb->jprobe_saved_regs.sp;

	long orig_sp = kernel_stack_pointer(regs);

	struct jprobe *jp = container_of(p, struct jprobe, kp);

	extern const char jprobe_return_break[];



	if (instruction_pointer(regs) != (u64) jprobe_return_break)

		return 0;