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Subject: Re: [PATCH v10 00/12] arm64: untag user pointers passed to the kernel
To:     Andrey Konovalov <andreyknvl@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        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>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Evgeniy Stepanov <eugenis@google.com>,
        Lee Smith <Lee.Smith@arm.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
        Jacob Bramley <Jacob.Bramley@arm.com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
        Chintan Pandya <cpandya@codeaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Szabolcs Nagy <Szabolcs.Nagy@arm.com>
References: <cover.1550839937.git.andreyknvl@google.com>
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Message-ID: <2ad5f897-25c0-90cf-f54f-827876873a0a@intel.com>
Date:   Fri, 22 Feb 2019 14:54:51 -0800
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On 2/22/19 4:53 AM, Andrey Konovalov wrote:
> The following testing approaches has been taken to find potential issues
> with user pointer untagging:
> 
> 1. Static testing (with sparse [3] and separately with a custom static
>    analyzer based on Clang) to track casts of __user pointers to integer
>    types to find places where untagging needs to be done.

First of all, it's really cool that you took this approach.  Sounds like
there was a lot of systematic work to fix up the sites in the existing
codebase.

But, isn't this a _bit_ fragile going forward?  Folks can't just "make
sparse" to find issues with missing untags.  This seems like something
where we would ideally add an __tagged annotation (or something) to the
source tree and then have sparse rules that can look for missed untags.