arm64: Prohibit instrumentation on arch_stack_walk()

Mark arch_stack_walk() as noinstr instead of notrace and inline functions
called from arch_stack_walk() as __always_inline so that user does not
put any instrumentations on it, because this function can be used from
return_address() which is used by lockdep.

Without this, if the kernel built with CONFIG_LOCKDEP=y, just probing
arch_stack_walk() via <tracefs>/kprobe_events will crash the kernel on
arm64.

 # echo p arch_stack_walk >> ${TRACEFS}/kprobe_events
 # echo 1 > ${TRACEFS}/events/kprobes/enable
  kprobes: Failed to recover from reentered kprobes.
  kprobes: Dump kprobe:
  .symbol_name = arch_stack_walk, .offset = 0, .addr = arch_stack_walk+0x0/0x1c0
  ------------[ cut here ]------------
  kernel BUG at arch/arm64/kernel/probes/kprobes.c:241!
  kprobes: Failed to recover from reentered kprobes.
  kprobes: Dump kprobe:
  .symbol_name = arch_stack_walk, .offset = 0, .addr = arch_stack_walk+0x0/0x1c0
  ------------[ cut here ]------------
  kernel BUG at arch/arm64/kernel/probes/kprobes.c:241!
  PREEMPT SMP
  Modules linked in:
  CPU: 0 PID: 17 Comm: migration/0 Tainted: G                 N 6.1.0-rc5+ gregkh#6
  Hardware name: linux,dummy-virt (DT)
  Stopper: 0x0 <- 0x0
  pstate: 600003c5 (nZCv DAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  pc : kprobe_breakpoint_handler+0x178/0x17c
  lr : kprobe_breakpoint_handler+0x178/0x17c
  sp : ffff8000080d3090
  x29: ffff8000080d3090 x28: ffff0df5845798c0 x27: ffffc4f59057a774
  x26: ffff0df5ffbba770 x25: ffff0df58f420f18 x24: ffff49006f641000
  x23: ffffc4f590579768 x22: ffff0df58f420f18 x21: ffff8000080d31c0
  x20: ffffc4f590579768 x19: ffffc4f590579770 x18: 0000000000000006
  x17: 5f6b636174735f68 x16: 637261203d207264 x15: 64612e202c30203d
  x14: 2074657366666f2e x13: 30633178302f3078 x12: 302b6b6c61775f6b
  x11: 636174735f686372 x10: ffffc4f590dc5bd8 x9 : ffffc4f58eb31958
  x8 : 00000000ffffefff x7 : ffffc4f590dc5bd8 x6 : 80000000fffff000
  x5 : 000000000000bff4 x4 : 0000000000000000 x3 : 0000000000000000
  x2 : 0000000000000000 x1 : ffff0df5845798c0 x0 : 0000000000000064
  Call trace:
  kprobes: Failed to recover from reentered kprobes.
  kprobes: Dump kprobe:
  .symbol_name = arch_stack_walk, .offset = 0, .addr = arch_stack_walk+0x0/0x1c0
  ------------[ cut here ]------------
  kernel BUG at arch/arm64/kernel/probes/kprobes.c:241!

Fixes: 39ef362 ("arm64: Make return_address() use arch_stack_walk()")
Cc: [email protected]
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Link: https://lore.kernel.org/r/166994751368.439920.3236636557520824664.stgit@devnote3
Signed-off-by: Will Deacon <[email protected]>

arch/arm64/kernel/stacktrace.c

@@ -23,8 +23,8 @@
  *
  * The regs must be on a stack currently owned by the calling task.
  */
-static inline void unwind_init_from_regs(struct unwind_state *state,
-					 struct pt_regs *regs)
+static __always_inline void unwind_init_from_regs(struct unwind_state *state,
+						  struct pt_regs *regs)
 {
 	unwind_init_common(state, current);
 
@@ -58,8 +58,8 @@ static __always_inline void unwind_init_from_caller(struct unwind_state *state)
  * duration of the unwind, or the unwind will be bogus. It is never valid to
  * call this for the current task.
  */
-static inline void unwind_init_from_task(struct unwind_state *state,
-					 struct task_struct *task)
+static __always_inline void unwind_init_from_task(struct unwind_state *state,
+						  struct task_struct *task)
 {
 	unwind_init_common(state, task);
 
@@ -186,7 +186,7 @@ void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 			: stackinfo_get_unknown();		\
 	})
 
-noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
+noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
 			      void *cookie, struct task_struct *task,
 			      struct pt_regs *regs)
 {