[PATCH v2 1/3] arm64: Prohibit instrumentation on arch_stack_walk()
Masami Hiramatsu (Google)
mhiramat at kernel.org
Mon Dec 5 16:41:37 PST 2022
On Fri, 2 Dec 2022 13:17:30 +0000
Mark Rutland <mark.rutland at arm.com> wrote:
> On Fri, Dec 02, 2022 at 11:18:33AM +0900, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat at kernel.org>
> >
> > 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.
>
> Hmmm... since arch_stack_walk is marked as notrace, that will be prohibited by
> default unless the kernel was built with CONFIG_KPROBE_EVENTS_ON_NOTRACE=y,
> and the commit message for that says:
>
> │ This option disables such protection and allows you to put kprobe │
> │ events on ftrace functions for debugging ftrace by itself. │
> │ Note that this might let you shoot yourself in the foot.
>
> ... and IIUC we generally don't expect people to set that, and that might be
> worth calling out in the commit message.
Yeah, but that is the feature for kprobe events, and not applied to
the kprobes itself. Maybe I should use a test kprobe module to
put a probe on it.
>
> > 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
>
> I had a go at testing this patch, and it fixes the crash with the reproducer
> above, but there are plenty of other instances in stacktrace.c that lead to the
> same sort of crash, e.g.
>
> # echo p stackinfo_get_task >> ${TRACEFS}/kprobe_events
> # echo 1 > ${TRACEFS}/events/kprobes/enable
Oops, thanks for pointing! Hmm, I thought stackinfo_get_task() is an
inlined function usually. Maybe we should make it nokprobe_inline.
But this is just one case. I need to scan all symbols to trace...
>
> ... so I think there's more that we need to do to fix this generally.
>
> Note: I found interesting functions to try tracing by looking at the output of:
>
> aarch64-linux-objdump -t arch/arm64/kernel/stacktrace.o | grep -w '.text'
>
> That all said, I think this patch is nice-to-have, and that we can address the
> other cases as a follow-up, so for this patch as-is (with or without some
> wording regarding CONFIG_KPROBE_EVENTS_ON_NOTRACE):
>
> Acked-by: Mark Rutland <mark.rutland at arm.com>
Thanks!
>
> Mark.
>
> > 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+ #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: 39ef362d2d45 ("arm64: Make return_address() use arch_stack_walk()")
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
> > ---
> > Changes in v2:
> > - Use noinstr instead of NOKPROBE_SYMBOL()
> > - Use __always_inline because nokprobe_inline will be changed if
> > CONFIG_KPROBES=n.
> > - Fix indentation.
> > ---
> > arch/arm64/kernel/stacktrace.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> > index 634279b3b03d..117e2c180f3c 100644
> > --- a/arch/arm64/kernel/stacktrace.c
> > +++ b/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)
> > {
> >
--
Masami Hiramatsu (Google) <mhiramat at kernel.org>
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