| Message ID | 1523513593.26617.106.camel@mtksdccf07 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 2018-04-12 at 14:13 +0800, Ji.Zhang wrote: > On Wed, 2018-04-11 at 11:46 +0100, Mark Rutland wrote: > > 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. > Thank you very much for your advice, they are very valuable. > According to your suggestion, the modified code as follows. > I did a little change that define MAX_NR_STACKS as the number of stacks, > instead of the number of stack spans. > > diff --git a/arch/arm64/include/asm/stacktrace.h > b/arch/arm64/include/asm/stacktrace.h > index 902f9ed..f235b86 100644 > --- a/arch/arm64/include/asm/stacktrace.h > +++ b/arch/arm64/include/asm/stacktrace.h > @@ -24,9 +24,18 @@ > #include <asm/ptrace.h> > #include <asm/sdei.h> > > +#ifndef CONFIG_VMAP_STACK > +#define MAX_NR_STACKS 2 > +#elif !defined(CONFIG_ARM_SDE_INTERFACE) > +#define MAX_NR_STACKS 3 > +#else > +#define MAX_NR_STACKS 4 > +#endif > + > struct stackframe { > unsigned long fp; > unsigned long pc; > + int nr_stacks; > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > int graph; > #endif > @@ -92,4 +101,20 @@ static inline bool on_accessible_stack(struct > task_struct *tsk, unsigned long sp > return false; > } > > + > +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..a09e247 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -27,6 +27,7 @@ > #include <asm/stack_pointer.h> > #include <asm/stacktrace.h> > > + > /* > * AArch64 PCS assigns the frame pointer to x29. > * > @@ -43,6 +44,7 @@ > int notrace unwind_frame(struct task_struct *tsk, struct stackframe > *frame) > { > unsigned long fp = frame->fp; > + bool same_stack; > > if (fp & 0xf) > return -EINVAL; > @@ -56,6 +58,13 @@ 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)); > > + 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; > + > #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..3b1c472 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -120,6 +120,7 @@ void dump_backtrace(struct pt_regs *regs, struct > task_struct *tsk) > frame.fp = thread_saved_fp(tsk); > frame.pc = thread_saved_pc(tsk); > } > + frame.nr_stacks = 1; > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > frame.graph = tsk->curr_ret_stack; > #endif Hi all sirs, Since the discussion is far away with the original topic of this patch, I have submitted a new patch: "arm64: avoid potential infinity loop in dump_backtrace" based on the latest sample code. We can switch to the new mail for more discussions. Thanks, Ji
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 902f9ed..f235b86 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -24,9 +24,18 @@ #include <asm/ptrace.h> #include <asm/sdei.h> +#ifndef CONFIG_VMAP_STACK +#define MAX_NR_STACKS 2 +#elif !defined(CONFIG_ARM_SDE_INTERFACE) +#define MAX_NR_STACKS 3 +#else +#define MAX_NR_STACKS 4 +#endif + struct stackframe { unsigned long fp; unsigned long pc; + int nr_stacks; #ifdef CONFIG_FUNCTION_GRAPH_TRACER int graph; #endif @@ -92,4 +101,20 @@ static inline bool on_accessible_stack(struct task_struct *tsk, unsigned long sp return false; } + +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..a09e247 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -27,6 +27,7 @@ #include <asm/stack_pointer.h> #include <asm/stacktrace.h> + /* * AArch64 PCS assigns the frame pointer to x29. * @@ -43,6 +44,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) { unsigned long fp = frame->fp; + bool same_stack; if (fp & 0xf) return -EINVAL; @@ -56,6 +58,13 @@ 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)); + 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; + #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..3b1c472 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -120,6 +120,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) frame.fp = thread_saved_fp(tsk); frame.pc = thread_saved_pc(tsk); } + frame.nr_stacks = 1; #ifdef CONFIG_FUNCTION_GRAPH_TRACER frame.graph = tsk->curr_ret_stack;