linux-kernel - Re: [PATCH v10 00/12] arm64: untag user pointers passed to the kernel

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Date:   Fri, 22 Feb 2019 14:54:51 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v10 00/12] arm64: untag user pointers passed to the kernel

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.