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Date:   Thu, 23 May 2019 21:11:05 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Khalid Aziz <khalid.aziz@oracle.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Evgenii Stepanov <eugenis@google.com>,
        Andrey Konovalov <andreyknvl@google.com>,
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Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
Message-ID: <20190523201105.oifkksus4rzcwqt4@mbp>
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Hi Khalid,

On Thu, May 23, 2019 at 11:51:40AM -0600, Khalid Aziz wrote:
> On 5/21/19 6:04 PM, Kees Cook wrote:
> > As an aside: I think Sparc ADI support in Linux actually side-stepped
> > this[1] (i.e. chose "solution 1"): "All addresses passed to kernel must
> > be non-ADI tagged addresses." (And sadly, "Kernel does not enable ADI
> > for kernel code.") I think this was a mistake we should not repeat for
> > arm64 (we do seem to be at least in agreement about this, I think).
> > 
> > [1] https://lore.kernel.org/patchwork/patch/654481/
> 
> That is a very early version of the sparc ADI patch. Support for tagged
> addresses in syscalls was added in later versions and is in the patch
> that is in the kernel.

I tried to figure out but I'm not familiar with the sparc port. How did
you solve the tagged address going into various syscall implementations
in the kernel (e.g. sys_write)? Is the tag removed on kernel entry or it
ends up deeper in the core code?

Thanks.

-- 
Catalin