From: Christoph Hellwig <hch@infradead.org>
To: Jann Horn <jannh@google.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org,
Dave Kleikamp <shaggy@linux.vnet.ibm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
kernel list <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
sparclinux@vger.kernel.org,
Anthony Yznaga <anthony.yznaga@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/2] mm/mprotect: Call arch_validate_prot under mmap_lock and with length
Date: Thu, 8 Oct 2020 07:21:40 +0100 [thread overview]
Message-ID: <20201008062140.GA24315@infradead.org> (raw)
In-Reply-To: <CAG48ez3kjTeVtQcjQerYYRs7sX5qq3O7SU-FEaYLNXisFmAeOg@mail.gmail.com>
On Wed, Oct 07, 2020 at 04:42:55PM +0200, Jann Horn wrote:
> > > @@ -43,7 +43,7 @@ static inline long do_mmap2(unsigned long addr, size_t len,
> > > {
> > > long ret = -EINVAL;
> > >
> > > - if (!arch_validate_prot(prot, addr))
> > > + if (!arch_validate_prot(prot, addr, len))
> >
> > This call isn't under mmap lock. I also find it rather weird as the
> > generic code only calls arch_validate_prot from mprotect, only powerpc
> > also calls it from mmap.
> >
> > This seems to go back to commit ef3d3246a0d0
> > ("powerpc/mm: Add Strong Access Ordering support")
>
> I'm _guessing_ the idea in the generic case might be that mmap()
> doesn't check unknown bits in the protection flags, and therefore
> maybe people wanted to avoid adding new error cases that could be
> caused by random high bits being set? So while the mprotect() case
> checks the flags and refuses unknown values, the mmap() code just lets
> the architecture figure out which bits are actually valid to set (via
> arch_calc_vm_prot_bits()) and silently ignores the rest?
>
> And powerpc apparently decided that they do want to error out on bogus
> prot values passed to their version of mmap(), and in exchange, assume
> in arch_calc_vm_prot_bits() that the protection bits are valid?
The problem really is that now programs behave different on powerpc
compared to all other architectures.
> powerpc's arch_validate_prot() doesn't actually need the mmap lock, so
> I think this is fine-ish for now (as in, while the code is a bit
> unclean, I don't think I'm making it worse, and I don't think it's
> actually buggy). In theory, we could move the arch_validate_prot()
> call over into the mmap guts, where we're holding the lock, and gate
> it on the architecture or on some feature CONFIG that powerpc can
> activate in its Kconfig. But I'm not sure whether that'd be helping or
> making things worse, so when I sent this patch, I deliberately left
> the powerpc stuff as-is.
For now I'd just duplicate the trivial logic from arch_validate_prot
in the powerpc version of do_mmap2 and add a comment that this check
causes a gratious incompatibility to all other architectures. And then
hope that the powerpc maintainers fix it up :)
next prev parent reply other threads:[~2020-10-08 6:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 7:39 [PATCH 1/2] mm/mprotect: Call arch_validate_prot under mmap_lock and with length Jann Horn
2020-10-07 7:39 ` [PATCH 2/2] sparc: Check VMA range in sparc_validate_prot() Jann Horn
2020-10-07 12:36 ` Christoph Hellwig
2020-10-07 20:15 ` Khalid Aziz
2020-10-07 12:35 ` [PATCH 1/2] mm/mprotect: Call arch_validate_prot under mmap_lock and with length Christoph Hellwig
2020-10-07 14:42 ` Jann Horn
2020-10-08 6:21 ` Christoph Hellwig [this message]
2020-10-08 10:34 ` Michael Ellerman
2020-10-08 11:03 ` Catalin Marinas
2020-10-07 20:14 ` Khalid Aziz
2020-10-10 11:09 ` Catalin Marinas
2020-10-12 17:03 ` Khalid Aziz
2020-10-12 17:22 ` Catalin Marinas
2020-10-12 19:14 ` Khalid Aziz
2020-10-13 9:16 ` Catalin Marinas
2020-10-14 21:21 ` Khalid Aziz
2020-10-14 22:29 ` Jann Horn
2020-10-15 9:05 ` Catalin Marinas
2020-10-15 14:53 ` Khalid Aziz
2020-10-08 10:12 ` Catalin Marinas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201008062140.GA24315@infradead.org \
--to=hch@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=anthony.yznaga@oracle.com \
--cc=benh@kernel.crashing.org \
--cc=catalin.marinas@arm.com \
--cc=davem@davemloft.net \
--cc=jannh@google.com \
--cc=khalid.aziz@oracle.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
--cc=shaggy@linux.vnet.ibm.com \
--cc=sparclinux@vger.kernel.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).