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Message-ID: <201909162003.FEEAC65@keescook>
Date: Mon, 16 Sep 2019 20:05:00 -0700
From: Kees Cook <keescook@...omium.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH] usercopy: Skip HIGHMEM page checking
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
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