From 3b7d14e9f3f1efd4c4348800e977fd1ce4ca660e Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 21 Jul 2016 09:44:17 +0100 Subject: [PATCH] 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: Marc Zyngier Signed-off-by: Catalin Marinas --- arch/arm64/kernel/probes/kprobes.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c index 09f8ae98da5a..973c15df5211 100644 --- a/arch/arm64/kernel/probes/kprobes.c +++ b/arch/arm64/kernel/probes/kprobes.c @@ -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" - : - : "r"(&kcb->jprobe_saved_regs.sp), - "I"(BRK64_ESR_KPROBES) - : "memory"); + asm volatile(" mov sp, %0 \n" + "jprobe_return_break: brk %1 \n" + : + : "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; -- 2.20.1