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Date:   Thu, 28 Jun 2018 11:27:42 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc:     Mark Rutland <Mark.Rutland@arm.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
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        Chintan Pandya <cpandya@codeaurora.org>,
        Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
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Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel
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On Thu, Jun 28, 2018 at 08:17:59AM +0200, Luc Van Oostenryck wrote:
> On Wed, Jun 27, 2018 at 06:17:58PM +0100, Catalin Marinas wrote:
> > sparse is indeed an option. The current implementation doesn't warn on
> > an explicit cast from (void __user *) to (unsigned long) since that's a
> > valid thing in the kernel. I couldn't figure out if there's any other
> > __attribute__ that could be used to warn of such conversion.
> 
> sparse doesn't have such attribute but would an new option that would warn
> on such cast be a solution for your case?

I can't tell for sure whether such sparse option would be the full
solution but detecting explicit __user pointer casts to long is a good
starting point. So far this patchset pretty much relies on detecting
a syscall failure and trying to figure out why, patching the kernel. It
doesn't really scale.

As a side note, we have cases in the user-kernel ABI where the user
address type is "unsigned long": mmap() and friends. My feedback on an
early version of this patchset was to always require untagged pointers
coming from user space on such syscalls, so no need for explicit
untagging.

-- 
Catalin