[kernel-hardening] Re: [PATCH] Provide useful debugging information for VM_BUG

[Michal Hocko <mhocko@kernel.org>]

On Tue 19-12-17 05:32:36, Matthew Wilcox wrote:
> 
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> With the recent addition of hashed kernel pointers, places which need
> to produce useful debug output have to specify %px, not %p.  This patch
> fixes all the VM debug to use %px.  This is appropriate because it's
> debug output that the user should never be able to trigger, and kernel
> developers need to see the actual pointers.

Agreed. This is essentially a BUG_ON so we shouldn't hide information.
I am just wondering why %px rather than %lx (like __show_regs e.g.)?
 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> diff --git a/mm/debug.c b/mm/debug.c
> index d947f3e03b0d..56e2d9125ea5 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -50,7 +50,7 @@ void __dump_page(struct page *page, const char *reason)
>  	 */
>  	int mapcount = PageSlab(page) ? 0 : page_mapcount(page);
>  
> -	pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
> +	pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx",
>  		  page, page_ref_count(page), mapcount,
>  		  page->mapping, page_to_pgoff(page));
>  	if (PageCompound(page))
> @@ -69,7 +69,7 @@ void __dump_page(struct page *page, const char *reason)
>  
>  #ifdef CONFIG_MEMCG
>  	if (page->mem_cgroup)
> -		pr_alert("page->mem_cgroup:%p\n", page->mem_cgroup);
> +		pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup);
>  #endif
>  }
>  
> @@ -84,10 +84,10 @@ EXPORT_SYMBOL(dump_page);
>  
>  void dump_vma(const struct vm_area_struct *vma)
>  {
> -	pr_emerg("vma %p start %p end %p\n"
> -		"next %p prev %p mm %p\n"
> -		"prot %lx anon_vma %p vm_ops %p\n"
> -		"pgoff %lx file %p private_data %p\n"
> +	pr_emerg("vma %px start %px end %px\n"
> +		"next %px prev %px mm %px\n"
> +		"prot %lx anon_vma %px vm_ops %px\n"
> +		"pgoff %lx file %px private_data %px\n"
>  		"flags: %#lx(%pGv)\n",
>  		vma, (void *)vma->vm_start, (void *)vma->vm_end, vma->vm_next,
>  		vma->vm_prev, vma->vm_mm,
> @@ -100,27 +100,27 @@ EXPORT_SYMBOL(dump_vma);
>  
>  void dump_mm(const struct mm_struct *mm)
>  {
> -	pr_emerg("mm %p mmap %p seqnum %d task_size %lu\n"
> +	pr_emerg("mm %px mmap %px seqnum %d task_size %lu\n"
>  #ifdef CONFIG_MMU
> -		"get_unmapped_area %p\n"
> +		"get_unmapped_area %px\n"
>  #endif
>  		"mmap_base %lu mmap_legacy_base %lu highest_vm_end %lu\n"
> -		"pgd %p mm_users %d mm_count %d pgtables_bytes %lu map_count %d\n"
> +		"pgd %px mm_users %d mm_count %d pgtables_bytes %lu map_count %d\n"
>  		"hiwater_rss %lx hiwater_vm %lx total_vm %lx locked_vm %lx\n"
>  		"pinned_vm %lx data_vm %lx exec_vm %lx stack_vm %lx\n"
>  		"start_code %lx end_code %lx start_data %lx end_data %lx\n"
>  		"start_brk %lx brk %lx start_stack %lx\n"
>  		"arg_start %lx arg_end %lx env_start %lx env_end %lx\n"
> -		"binfmt %p flags %lx core_state %p\n"
> +		"binfmt %px flags %lx core_state %px\n"
>  #ifdef CONFIG_AIO
> -		"ioctx_table %p\n"
> +		"ioctx_table %px\n"
>  #endif
>  #ifdef CONFIG_MEMCG
> -		"owner %p "
> +		"owner %px "
>  #endif
> -		"exe_file %p\n"
> +		"exe_file %px\n"
>  #ifdef CONFIG_MMU_NOTIFIER
> -		"mmu_notifier_mm %p\n"
> +		"mmu_notifier_mm %px\n"
>  #endif
>  #ifdef CONFIG_NUMA_BALANCING
>  		"numa_next_scan %lu numa_scan_offset %lu numa_scan_seq %d\n"
> 
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-- 
Michal Hocko
SUSE Labs