From mboxrd@z Thu Jan  1 00:00:00 1970
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
Date: Thu, 23 May 2019 21:11:05 +0100
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To: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Kees Cook <keescook@chromium.org>, Evgenii Stepanov <eugenis@google.com>, Andrey Konovalov <andreyknvl@google.com>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Linux Memory Management List <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will.deacon@arm.com>, Mark Rutland <mark.rutland@arm.com>, Andrew Morton <akpm@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Yishai Hadas <yishaih@mellanox.com>, Felix Kuehling <Felix.Kuehling@amd.com>
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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