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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 30 Aug 2018 13:48:15 +0200
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Subject: Re: [PATCH v6 00/11] arm64: untag user pointers passed to the kernel
To:     Catalin Marinas <catalin.marinas@arm.com>
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>,
        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>,
        Andrey Konovalov <andreyknvl@google.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>,
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On Thu, Aug 30, 2018 at 1:41 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> arm64 has a feature called Top Byte Ignore, which allows to embed pointer
> tags into the top byte of each pointer. Userspace programs (such as
> HWASan, a memory debugging tool [1]) might use this feature and pass
> tagged user pointers to the kernel through syscalls or other interfaces.
>
> This patch makes a few of the kernel interfaces accept tagged user
> pointers. The kernel is already able to handle user faults with tagged
> pointers and has the untagged_addr macro, which this patchset reuses.
>
> Thanks!
>
> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
>
> Changes in v6:
> - Added annotations for user pointer casts found by sparse.

Hi Catalin,

I've added annotations for the user pointer casts pointed by the new
sparse flag -Wcast-from-as as you asked. I've used __force casts
instead of adding specialized macros.

There are also non annotated casts for other pointer types (iomem,
rcu) which are detected with the new flag, should I annotate those as
well?

I'm not sure though what value would that bring though, as there are
~3000 various sparse warnings produced with the default flags anyway.

WDYT?

Thanks!

[1] https://github.com/lucvoo/sparse-dev/commit/5f960cb10f56ec2017c128ef9d16060e0145f292