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

[Yury Norov]

On Thu, May 12, 2016 at 11:19:21AM +0200, Arnd Bergmann wrote:
> 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@xxxxxxxxxxxxxxxxxx>
> > 
> 
> 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
> 

OK, will do

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