Re: [PATCH v2] stackdepot: ignore junk last entry in case of switch from user mode.

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

On 10/11/2017 03:43 PM, Maninder Singh wrote:
> Issue observed on ARM.
> 
> Whenever there is switch from user mode, we end up with invalid last entry
> with some user space address as below:-
> 
>  save_stack+0x40/0xec
>  __set_page_owner+0x2c/0x64
> ....
> ....
>  __handle_domain_irq+0x9c/0x130
>  gic_handle_irq+0x40/0x80
>  __irq_usr+0x4c/0x60
>  0xb6507818
> 

Sounds like an ARM issue to me.

...
 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index f87d138..a045748 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -214,6 +214,13 @@ depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
>  	if (unlikely(trace->nr_entries == 0))
>  		goto fast_exit;
>  
> +	/* 
> +	 * Ignore last entry if it belongs to user space

And if it belongs to module too. NACK.


> +	 * in case of switch from user mode.
> +	 */
> +	if (!kernel_text_address(trace->entries[trace->nr_entries - 1]))
> +		trace->nr_entries--;
> +
>  	hash = hash_stack(trace->entries, trace->nr_entries);
>  	bucket = &stack_table[hash & STACK_HASH_MASK];
>  
>