Re: [PATCH 2/3] mm: page table check

[Jiri Slaby]

On 23. 11. 21, 22:48, Pasha Tatashin wrote:
> Check user page table entries at the time they are added and removed.
>
> Allows to synchronously catch memory corruption issues related to
> double mapping.
>
> When a pte for an anonymous page is added into page table, we verify
> that this pte does not already point to a file backed page, and vice
> versa if this is a file backed page that is being added we verify that
> this page does not have an anonymous mapping
>
> We also enforce that read-only sharing for anonymous pages is allowed
> (i.e. cow after fork). All other sharing must be for file pages.
>
> Page table check allows to protect and debug cases where "struct page"
> metadata became corrupted for some reason. For example, when refcnt or
> mapcount become invalid.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
...
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -62,6 +62,30 @@ config PAGE_OWNER
>   
>   	  If unsure, say N.
>   
> +config PAGE_TABLE_CHECK
> +	bool "Check for invalid mappings in user page tables"
> +	depends on ARCH_SUPPORTS_PAGE_TABLE_CHECK
> +	select PAGE_EXTENSION
> +	help
> +	  Check that anonymous page is not being mapped twice with read write
> +	  permissions. Check that anonymous and file pages are not being
> +	  erroneously shared. Since the checking is performed at the time
> +	  entries are added and removed to user page tables, leaking, corruption
> +	  and double mapping problems are detected synchronously.
> +
> +	  If unsure say "n".
> +
> +config PAGE_TABLE_CHECK_ENFORCED
> +	bool "Enforce the page table checking by defauled"

s/defauled/default/

regards,
--
js
suse labs