linux-hardening - Re: [PATCH v3 3/3] mm/usercopy: Detect compound page overruns

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Date:   Mon, 13 Dec 2021 23:44:33 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 3/3] mm/usercopy: Detect compound page overruns

On Mon, Dec 13, 2021 at 12:52:22PM -0800, Kees Cook wrote:
> On Mon, Dec 13, 2021 at 02:27:03PM +0000, Matthew Wilcox (Oracle) wrote:
> > Move the compound page overrun detection out of
> > CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people.
> 
> I'd argue that everything else enabled by USERCOPY_PAGESPAN could be
> removed now too. Do you want to add a 4th patch to rip that out?
> 
> https://github.com/KSPP/linux/issues/163

I don't mind ... is it your assessment that it's not worth checking for
a copy_to/from_user that spans a boundary between a reserved and
!reserved page, or overlaps the boundary of rodata/bss/data/CMA?

I have no basis on which to judge that, so it's really up to you.