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

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Message-ID: <6abc8c6a-c7aa-72ec-8a4e-7dcfeb9ea09b@intel.com>
Date:   Tue, 26 Feb 2019 09:35:26 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     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 <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        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 2/26/19 9:18 AM, Andrey Konovalov wrote:
>> 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.
> This has been suggested before, search for __untagged here [1].
> However there are many places in the kernel where a __user pointer is
> casted into unsigned long and passed further. I'm not sure if it's
> possible apply a __tagged/__untagged kind of attribute to non-pointer
> types, is it?
> 
> [1] https://patchwork.kernel.org/patch/10581535/

I believe we have sparse checking __GFP_* flags.  We also have a gfp_t
for them and I'm unsure whether the sparse support is tied to _that_ or
whether it's just by tagging the type itself as being part of a discrete
address space.