linux-kernel - Re: [RFC6 PATCH v6 00/21] ILP32 for ARM64

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Date:	Thu, 12 May 2016 11:19:21 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Yury Norov <ynorov@...iumnetworks.com>, catalin.marinas@....com,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-s390@...r.kernel.org, pinskia@...il.com,
	Prasun.Kapoor@...iumnetworks.com, heiko.carstens@...ibm.com,
	linux-doc@...r.kernel.org, Nathan_Lynch@...tor.com, agraf@...e.de,
	klimov.linux@...il.com, broonie@...nel.org,
	bamvor.zhangjian@...wei.com, schwab@...e.de,
	schwidefsky@...ibm.com, joseph@...esourcery.com,
	christoph.muellner@...obroma-systems.com
Subject: Re: [RFC6 PATCH v6 00/21] ILP32 for ARM64

On Thursday 12 May 2016 03:20:00 Yury Norov wrote:
> 
> I debugged preadv02 and pwritev02 failures and found very weird bug.
> Test passes {iovec_base = 0xffffffff, iovec_len = 64} as one element
> of vector, and kernel reports successful read/write.
> 
> There are 2 problems:
> 1. How kernel allows such address to be passed to fs subsystem;
> 2. How fs successes to read/write at non-mapped, and in fact non-user
> address.
> 
> I don't know the answer on 2'nd question, and it might be something
> generic. But I investigated first problem.
> 
> The problem is that compat_rw_copy_check_uvector() uses access_ok() to
> validate user address, and on arm64 it ends up with checking buffer
> end against current_thread_info()->addr_limit.
> 
> current_thread_info()->addr_limit for ilp32, and most probably for
> aarch32 is equal to aarch64 one, and so adress_ok() doesn't fail.
> It happens because on thread creation we call flush_old_exec() to set 
> addr_limit, and completely ignore compat mode there.
> 
> This patch fixes it. It also fixes USER_DS macro to return different
> values depending on compat.
> 
> This patch is enough to handle preadv02 and pwritev02, but problem #2
> is still there.
> 
> Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
> 

Good catch!

Can you do a version of this patch that works on the current
mainline kernel and can be backported to fix aarch32 emulation?

For ilp32 mode, I think we can better fix arch/arm64/kernel/binfmt_ilp32.c
as it is introduced.

	Arnd