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Date: Thu, 12 Feb 2015 17:07:15 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Szabolcs Nagy <nsz@...t70.net>
Cc: musl@...ts.openwall.com, Rich Felker <dalias@...c.org>,
Andrew Pinski <apinski@...ium.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"pinskia@...il.com" <pinskia@...il.com>,
"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
Marcus Shawcroft <Marcus.Shawcroft@....com>
Subject: Re: Re: [PATCHv3 00/24] ILP32 support in ARM64
On Thu, Feb 12, 2015 at 09:12:34AM +0100, Szabolcs Nagy wrote:
> * Szabolcs Nagy <nsz@...t70.net> [2015-02-11 20:05:37 +0100]:
> > (i think this is also a problem if userspace code uses syscall(2) directly,
> > libc cannot possibly know where to signextend and the kernel side does not
> > do the fixup right now)
>
> nobody picked up this issue, is this resolved?
>
> ie. if userspace calls syscall(SYS_foo,...) directly with 32bit
> longs does it always work out correctly on the kernel side?
I think the only way to solve this is to have syscall wrappers in the
kernel rather than glibc.
> the sign extension is a problem for signed long arguments,
> i only found these in the kernel:
>
> fs/buffer.c:SYSCALL_DEFINE2(bdflush, int, func, long, data)
This is part of the deprecated syscalls, it is not used on new user
ABIs.
> fs/open.c:SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
The kernel uses a long (64-bit) here and the user ABI defines this as an
off_t. With x32, this should be a long long (__kernel_long_t), so not a
problem.
> fs/aio.c:SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
> fs/aio.c- struct iocb __user * __user *, iocbpp)
>
> fs/aio.c:SYSCALL_DEFINE5(io_getevents, aio_context_t, ctx_id,
> fs/aio.c- long, min_nr,
> fs/aio.c- long, nr,
These would need some int->long conversion for nr, min_nr (it may be
done in x32 glibc already but as you said it would not work via
syscall() directly).
> kernel/ptrace.c:SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
> kernel/ptrace.c- unsigned long, data)
The pid in user space would be pid_t which is 32-bit. The kernel seems
to use it as pid_t afterwards, so looks safe. For addr and data, I guess
it needs wrappers to zero the top part.
> ipc/syscall.c:SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
> ipc/syscall.c- unsigned long, third, void __user *, ptr, long, fifth)
ipc(2) shows the first, second, third as ints. I guess some kernel
wrapper is needed here as well.
--
Catalin
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