linux-kernel - Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180627171757.amucnh5znld45cpc@armageddon.cambridge.arm.com>
Date:   Wed, 27 Jun 2018 18:17:58 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Ramana Radhakrishnan <ramana.radhakrishnan@....com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Rutland <Mark.Rutland@....com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Will Deacon <Will.Deacon@....com>,
        Kostya Serebryany <kcc@...gle.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Al Viro <viro@...iv.linux.org.uk>, nd <nd@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lee Smith <Lee.Smith@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Robin Murphy <Robin.Murphy@....com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

On Wed, Jun 27, 2018 at 04:08:09PM +0100, Ramana Radhakrishnan wrote:
> On 27/06/2018 16:05, Andrey Konovalov wrote:
> > On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas
> > <catalin.marinas@....com> wrote:
> >> On Tue, Jun 26, 2018 at 02:47:50PM +0200, Andrey Konovalov wrote:
> >>> On Wed, Jun 20, 2018 at 5:24 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> >>>> arm64 has a feature called Top Byte Ignore, which allows to embed pointer
> >>>> tags into the top byte of each pointer. Userspace programs (such as
> >>>> HWASan, a memory debugging tool [1]) might use this feature and pass
> >>>> tagged user pointers to the kernel through syscalls or other interfaces.
> >>>>
> >>>> This patch makes a few of the kernel interfaces accept tagged user
> >>>> pointers. The kernel is already able to handle user faults with tagged
> >>>> pointers and has the untagged_addr macro, which this patchset reuses.
> >>>>
> >>>> We're not trying to cover all possible ways the kernel accepts user
> >>>> pointers in one patchset, so this one should be considered as a start.
> >>>>
> >>>> Thanks!
> >>>>
> >>>> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
> >>>
> >>> Is there anything I should do to move forward with this?
> >>>
> >>> I've received zero replies to this patch set (v3 and v4) over the last
> >>> month.
> >>
> >> The patches in this series look fine but my concern is that they are not
> >> sufficient and we don't have (yet?) a way to identify where such
> >> annotations are required. You even say in patch 6 that this is "some
> >> initial work for supporting non-zero address tags passed to the kernel".
> >> Unfortunately, merging (or relaxing) an ABI without a clear picture is
> >> not really feasible.
> >>
> >> While I support this work, as a maintainer I'd like to understand
> >> whether we'd be in a continuous chase of ABI breaks with every kernel
> >> release or we have a better way to identify potential issues. Is there
> >> any way to statically analyse conversions from __user ptr to long for
> >> example? Or, could we get the compiler to do this for us?
> > 
> > OK, got it, I'll try to figure out a way to find these conversions.
> 
> This sounds like the kind of thing we should be able to get sparse to do
> already, no ? It's been many years since I last looked at it but I
> thought sparse was the tool of choice in the kernel to do this kind of
> checking.

sparse is indeed an option. The current implementation doesn't warn on
an explicit cast from (void __user *) to (unsigned long) since that's a
valid thing in the kernel. I couldn't figure out if there's any other
__attribute__ that could be used to warn of such conversion.

-- 
Catalin