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 <redacted>

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