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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Fri, 3 Aug 2018 16:59:18 +0200
Message-ID: <CAAeHK+xTxPhfbVTNxcbsx7VdwQ21Bt-vo2ZU1tEM1_JX7uKnng@mail.gmail.com>
Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        linux-doc@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
        Kostya Serebryany <kcc@google.com>,
        linux-kselftest@vger.kernel.org,
        Chintan Pandya <cpandya@codeaurora.org>,
        Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        linux-arch@vger.kernel.org, Jacob Bramley <Jacob.Bramley@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Evgeniy Stepanov <eugenis@google.com>,
        Kees Cook <keescook@chromium.org>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lee Smith <Lee.Smith@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Robin Murphy <robin.murphy@arm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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On Thu, Aug 2, 2018 at 5:00 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> On Wed, Aug 1, 2018 at 7:42 PM, Catalin Marinas <catalin.marinas@arm.com> wrote:
>> On Mon, Jul 16, 2018 at 01:25:59PM +0200, Andrey Konovalov wrote:
>>> On Thu, Jun 28, 2018 at 9:30 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
>>> So the checker reports ~100 different places where a __user pointer
>>> being casted. I've looked through them and found 3 places where we
>>> need to add untagging. Source code lines below come from 4.18-rc2+
>>> (6f0d349d).
>> [...]
>>> I'll add the 3 patches with fixes to v5 of this patchset.
>>
>> Thanks for investigating. You can fix those three places in your code
>
> OK, will do.
>
>> but I was rather looking for a way to check such casting in the future
>> for newly added code. While for the khwasan we can assume it's a debug
>> option, the tagged user pointers are ABI and we need to keep it stable.
>>
>> We could we actually add some macros for explicit conversion between
>> __user ptr and long and silence the warning there (I guess this would
>> work better for sparse). We can then detect new ptr to long casts as
>> they appear. I just hope that's not too intrusive.
>>
>> (I haven't tried the sparse patch yet, hopefully sometime this week)
>
> Haven't look at that sparse patch yet myself, but sounds doable.
> Should these macros go into this patchset or should they go
> separately?

Started looking at this. When I run sparse with default checks enabled
(make C=1) I get countless warnings. Does anybody actually use it?