Re: [PATCH] usercopy: Skip HIGHMEM page checking

[Kees Cook]

On Mon, Sep 16, 2019 at 05:32:09PM -0700, Matthew Wilcox wrote:
> On Mon, Sep 16, 2019 at 02:32:56PM -0700, Kees Cook wrote:
> > When running on a system with >512MB RAM with a 32-bit kernel built with:
> > 
> > 	CONFIG_DEBUG_VIRTUAL=y
> > 	CONFIG_HIGHMEM=y
> > 	CONFIG_HARDENED_USERCOPY=y
> > 
> > all execve()s will fail due to argv copying into kmap()ed pages, and on
> > usercopy checking the calls ultimately of virt_to_page() will be looking
> > for "bad" kmap (highmem) pointers due to CONFIG_DEBUG_VIRTUAL=y:
> 
> I don't understand why you want to skip the check.  We must not cross a
> page boundary of a kmapped page.

That requires a new test which hasn't existed before. First I need to
fix the bug, and then we can add a new test and get that into -next,
etc.

-- 
Kees Cook