| Message ID | 1523428228.26617.100.camel@mtksdccf07 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Apr 11, 2018 at 02:30:28PM +0800, Ji.Zhang wrote: > On Mon, 2018-04-09 at 12:26 +0100, Mark Rutland wrote: > > On Sun, Apr 08, 2018 at 03:58:48PM +0800, Ji.Zhang wrote: > > > Yes, I see where the loop is, I have missed that the loop may cross > > > different stacks. > > > Define a nesting order and check against is a good idea, and it can > > > resolve the issue exactly, but as you mentioned before, we have no idea > > > how to handle with overflow and sdei stack, and the nesting order is > > > strongly related with the scenario of the stack, which means if someday > > > we add another stack, we should consider the relationship of the new > > > stack with other stacks. From the perspective of your experts, is that > > > suitable for doing this in unwind? > > > > > > Or could we just find some way easier but not so accurate, eg. > > > Proposal 1: > > > When we do unwind and detect that the stack spans, record the last fp of > > > previous stack and next time if we get into the same stack, compare it > > > with that last fp, the new fp should still smaller than last fp, or > > > there should be potential loop. > > > For example, when we unwind from irq to task, we record the last fp in > > > irq stack such as last_irq_fp, and if it unwind task stack back to irq > > > stack, no matter if it is the same irq stack with previous, just let it > > > go and compare the new irq fp with last_irq_fp, although the process may > > > be wrong since from task stack it could not unwind to irq stack, but the > > > whole process will eventually stop. > > > > I agree that saving the last fp per-stack could work. > > > > > Proposal 2: > > > So far we have four types of stack: task, irq, overflow and sdei, could > > > we just assume that the MAX number of stack spanning is just 3 > > > times?(task->irq->overflow->sdei or task->irq->sdei->overflow), if yes, > > > we can just check the number of stack spanning when we detect the stack > > > spans. > > > > I also agree that counting the number of stack transitions will prevent > > an inifinite loop, even if less accurately than proposal 1. > > > > I don't have a strong preference either way. > Thank you for your comment. > Compared with proposal 1 and 2, I decide to use proposal2 since > proposal1 seems a little complicated and it is not as easy as proposal2 > when new stack is added. > The sample is as below: > diff --git a/arch/arm64/include/asm/stacktrace.h > b/arch/arm64/include/asm/stacktrace.h > index 902f9ed..72d1f34 100644 > --- a/arch/arm64/include/asm/stacktrace.h > +++ b/arch/arm64/include/asm/stacktrace.h > @@ -92,4 +92,22 @@ static inline bool on_accessible_stack(struct > task_struct *tsk, unsigned long sp > return false; > } > > +#define MAX_STACK_SPAN 3 Depending on configuration we can have: * task * irq * overflow (optional with VMAP_STACK) * sdei (optional with ARM_SDE_INTERFACE && VMAP_STACK) So 3 isn't always correct. Also, could we please call this something like MAX_NR_STACKS? > +DECLARE_PER_CPU(int, num_stack_span); I'm pretty sure we can call unwind_frame() in a preemptible context, so this isn't safe. Put this counter into the struct stackframe, and call it something like nr_stacks; [...] > +DEFINE_PER_CPU(int, num_stack_span); As above, this can go. > + > /* > * AArch64 PCS assigns the frame pointer to x29. > * > @@ -56,6 +58,20 @@ int notrace unwind_frame(struct task_struct *tsk, > struct stackframe *frame) > frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); > frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); > > + if (!on_same_stack(tsk, fp, frame->fp)) { > + int num = (int)__this_cpu_read(num_stack_span); > + > + if (num >= MAX_STACK_SPAN) > + return -EINVAL; > + num++; > + __this_cpu_write(num_stack_span, num); > + fp = frame->fp + 0x8; > + } > + if (fp <= frame->fp) { > + pr_notice("fp invalid, stop unwind\n"); > + return -EINVAL; > + } I think this can be simplified to something like: bool same_stack; same_stack = on_same_stack(tsk, fp, frame->fp); if (fp <= frame->fp && same_stack) return -EINVAL; if (!same_stack && ++frame->nr_stacks > MAX_NR_STACKS) return -EINVAL; ... assuming we add nr_stacks to struct stackframe. Thanks, Mark.
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 902f9ed..72d1f34 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -92,4 +92,22 @@ static inline bool on_accessible_stack(struct task_struct *tsk, unsigned long sp return false; } +#define MAX_STACK_SPAN 3 +DECLARE_PER_CPU(int, num_stack_span); + +static inline bool on_same_stack(struct task_struct *tsk, + unsigned long sp1, unsigned long sp2) +{ + if (on_task_stack(tsk, sp1) && on_task_stack(tsk, sp2)) + return true; + if (on_irq_stack(sp1) && on_irq_stack(sp2)) + return true; + if (on_overflow_stack(sp1) && on_overflow_stack(sp2)) + return true; + if (on_sdei_stack(sp1) && on_sdei_stack(sp2)) + return true; + + return false; +} + #endif /* __ASM_STACKTRACE_H */ diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index d5718a0..db905e8 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -27,6 +27,8 @@ #include <asm/stack_pointer.h> #include <asm/stacktrace.h> +DEFINE_PER_CPU(int, num_stack_span); + /* * AArch64 PCS assigns the frame pointer to x29. * @@ -56,6 +58,20 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); + if (!on_same_stack(tsk, fp, frame->fp)) { + int num = (int)__this_cpu_read(num_stack_span); + + if (num >= MAX_STACK_SPAN) + return -EINVAL; + num++; + __this_cpu_write(num_stack_span, num); + fp = frame->fp + 0x8; + } + if (fp <= frame->fp) { + pr_notice("fp invalid, stop unwind\n"); + return -EINVAL; + } + #ifdef CONFIG_FUNCTION_GRAPH_TRACER if (tsk->ret_stack && (frame->pc == (unsigned long)return_to_handler)) { diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index eb2d151..e6b5181 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -102,6 +102,8 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) struct stackframe frame; int skip; + __this_cpu_write(num_stack_span, 0); + pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);