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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 28 Jun 2018 21:30:16 +0200
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Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Kees Cook <keescook@chromium.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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        Linux Memory Management List <linux-mm@kvack.org>,
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        LKML <linux-kernel@vger.kernel.org>,
        Chintan Pandya <cpandya@codeaurora.org>,
        Jacob Bramley <Jacob.Bramley@arm.com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
        Lee Smith <Lee.Smith@arm.com>,
        Kostya Serebryany <kcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
        Evgeniy Stepanov <eugenis@google.com>
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On Wed, Jun 27, 2018 at 5:05 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas
> <catalin.marinas@arm.com> wrote:
>> 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.

I've prototyped a checker on top of clang static analyzer (initially
looked at sparse, but couldn't find any documentation or examples).
The results are here [1], search for "warning: user pointer cast".
Sharing in case anybody wants to take a look, will look at them myself
tomorrow.

[1] https://gist.github.com/xairy/433edd5c86456a64026247cb2fef2115