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SubjectRe: [PATCH] x86/dumpstack/64: Add guard pages to stack_info
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On 2021/9/15 下午11:17, Peter Zijlstra wrote:
> On Wed, Sep 15, 2021 at 09:51:57AM +0800, 王贇 wrote:
>
>>> +
>>> + if (in_exception_stack_guard((void *)address))
>>> + pr_emerg("PANIC: exception stack guard: 0x%lx\n", address);
>>> #endif
>>>
>>> pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
>>>
>>
>> The panic triggered as below after the stack size recovered, I found this info
>> could be helpful, maybe we should keep it?
>
> Could you please test this?

I did some debug and found the issue, we are missing:

@@ -122,7 +137,10 @@ static __always_inline bool in_exception_stack(unsigned long *stack, struct stac
info->type = ep->type;
info->begin = (unsigned long *)begin;
info->end = (unsigned long *)end;
- info->next_sp = (unsigned long *)regs->sp;
+
+ if (!(ep->type & STACK_TYPE_GUARD))
+ info->next_sp = (unsigned long *)regs->sp;
+
return true;
}

as the guard page are not working as real stack I guess?

With that one things going on correctly, and some trivials below.

>
> ---
> Subject: x86/dumpstack/64: Add guard pages to stack_info
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Sep 15 17:12:59 CEST 2021
>
> Explicitly add the exception stack guard pages to stack_info and
> report on them from #DF.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/include/asm/cpu_entry_area.h | 3 +++
> arch/x86/include/asm/stacktrace.h | 3 ++-
> arch/x86/kernel/dumpstack_64.c | 17 ++++++++++++++++-
> arch/x86/kernel/traps.c | 17 ++++++++++++++++-
> 4 files changed, 37 insertions(+), 3 deletions(-)
>
> --- a/arch/x86/include/asm/cpu_entry_area.h
> +++ b/arch/x86/include/asm/cpu_entry_area.h
> @@ -61,6 +61,9 @@ enum exception_stack_ordering {
> #define CEA_ESTACK_OFFS(st) \
> offsetof(struct cea_exception_stacks, st## _stack)
>
> +#define CEA_EGUARD_OFFS(st) \
> + offsetof(struct cea_exception_stacks, st## _stack_guard)
> +
> #define CEA_ESTACK_PAGES \
> (sizeof(struct cea_exception_stacks) / PAGE_SIZE)
>
> --- a/arch/x86/include/asm/stacktrace.h
> +++ b/arch/x86/include/asm/stacktrace.h
> @@ -14,13 +14,14 @@
> #include <asm/switch_to.h>
>
> enum stack_type {
> - STACK_TYPE_UNKNOWN,
> + STACK_TYPE_UNKNOWN = 0,

Is this necessary?

> STACK_TYPE_TASK,
> STACK_TYPE_IRQ,
> STACK_TYPE_SOFTIRQ,
> STACK_TYPE_ENTRY,
> STACK_TYPE_EXCEPTION,
> STACK_TYPE_EXCEPTION_LAST = STACK_TYPE_EXCEPTION + N_EXCEPTION_STACKS-1,
> + STACK_TYPE_GUARD = 0x80,
> };
>
> struct stack_info {
> --- a/arch/x86/kernel/dumpstack_64.c
> +++ b/arch/x86/kernel/dumpstack_64.c
> @@ -32,9 +32,15 @@ const char *stack_type_name(enum stack_t
> {
> BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);
>
> + if (type == STACK_TYPE_TASK)
> + return "TASK";
> +
> if (type == STACK_TYPE_IRQ)
> return "IRQ";
>
> + if (type == STACK_TYPE_SOFTIRQ)
> + return "SOFTIRQ";
> +

Do we need one for GUARD too?

> if (type == STACK_TYPE_ENTRY) {
> /*
> * On 64-bit, we have a generic entry stack that we
> @@ -63,6 +69,11 @@ struct estack_pages {
> };
>
> #define EPAGERANGE(st) \
> + [PFN_DOWN(CEA_EGUARD_OFFS(st))] = { \
> + .offs = CEA_EGUARD_OFFS(st), \
> + .size = PAGE_SIZE, \
> + .type = STACK_TYPE_GUARD + \
> + STACK_TYPE_EXCEPTION + ESTACK_ ##st, }, \
> [PFN_DOWN(CEA_ESTACK_OFFS(st)) ... \
> PFN_DOWN(CEA_ESTACK_OFFS(st) + CEA_ESTACK_SIZE(st) - 1)] = { \
> .offs = CEA_ESTACK_OFFS(st), \
> @@ -111,10 +122,11 @@ static __always_inline bool in_exception
> k = (stk - begin) >> PAGE_SHIFT;
> /* Lookup the page descriptor */
> ep = &estack_pages[k];
> - /* Guard page? */
> + /* unknown entry */
> if (!ep->size)
> return false;
>
> +

Extra line?

Regards,
Michael Wang

> begin += (unsigned long)ep->offs;
> end = begin + (unsigned long)ep->size;
> regs = (struct pt_regs *)end - 1;
> @@ -193,6 +205,9 @@ int get_stack_info(unsigned long *stack,
> if (!get_stack_info_noinstr(stack, task, info))
> goto unknown;
>
> + if (info->type & STACK_TYPE_GUARD)
> + goto unknown;
> +
> /*
> * Make sure we don't iterate through any given stack more than once.
> * If it comes up a second time then there's something wrong going on:
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -461,6 +461,19 @@ DEFINE_IDTENTRY_DF(exc_double_fault)
> }
> #endif
>
> +#ifdef CONFIG_X86_64
> + {
> + struct stack_info info;
> +
> + if (get_stack_info_noinstr((void *)address, current, &info) &&
> + info.type & STACK_TYPE_GUARD) {
> + const char *name = stack_type_name(info.type & ~STACK_TYPE_GUARD);
> + pr_emerg("BUG: %s stack guard hit at %p (stack is %p..%p)\n",
> + name, (void *)address, info.begin, info.end);
> + }
> + }
> +#endif
> +
> pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
> die("double fault", regs, error_code);
> panic("Machine halted.");
> @@ -708,7 +721,9 @@ asmlinkage __visible noinstr struct pt_r
> sp = regs->sp;
> stack = (unsigned long *)sp;
>
> - if (!get_stack_info_noinstr(stack, current, &info) || info.type == STACK_TYPE_ENTRY ||
> + if (!get_stack_info_noinstr(stack, current, &info) ||
> + info.type & STACK_TYPE_GUARD ||
> + info.type == STACK_TYPE_ENTRY ||
> info.type >= STACK_TYPE_EXCEPTION_LAST)
> sp = __this_cpu_ist_top_va(VC2);
>
>

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