Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check.

[Kees Cook]

On December 4, 2024 5:56:34 AM GMT+10:00, Matthew Wilcox <wi...@infradead.org> 
wrote:
>On Tue, Dec 03, 2024 at 08:02:26PM +0100, Uladzislau Rezki wrote:
>
>I think there are a few other things we can try here.
>
>First, if the copy is small (and I still don't have an answer to that
>...), we can skip the vmalloc lookup if the copy doesn't cross a page
>boundary.

Yeah, this seems a reasonable optimization.

>Anyway, NACK to the original patch; that's just a horrible idea.

Right, please no debugfs knob. The point is to make sure the check cannot be 
disabled at runtime and to make the check a no-op. Please use the boot param to 
disable this check. 

-Kees

-- 
Kees Cook