Messages in this thread Patch in this message | | | Date | Tue, 6 Dec 2022 09:41:37 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH v2 1/3] arm64: Prohibit instrumentation on arch_stack_walk() |
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On Fri, 2 Dec 2022 13:17:30 +0000 Mark Rutland <mark.rutland@arm.com> wrote:
> On Fri, Dec 02, 2022 at 11:18:33AM +0900, Masami Hiramatsu (Google) wrote: > > From: Masami Hiramatsu (Google) <mhiramat@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@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@vger.kernel.org > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@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@kernel.org>
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