From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751492AbcEMIMK (ORCPT ); Fri, 13 May 2016 04:12:10 -0400 Received: from szxga04-in.huawei.com ([58.251.152.52]:45993 "EHLO szxga04-in.huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751288AbcEMIMA (ORCPT ); Fri, 13 May 2016 04:12:00 -0400 Subject: Re: [RFC6 PATCH v6 00/21] ILP32 for ARM64 To: Catalin Marinas , Yury Norov References: <1459894127-17698-1-git-send-email-ynorov@caviumnetworks.com> <20160512002000.GA30997@yury-N73SV> <20160512133533.GF11226@e104818-lin.cambridge.arm.com> <20160512134431.GB30205@yury-N73SV> <20160512140734.GG11226@e104818-lin.cambridge.arm.com> <20160512142457.GC30205@yury-N73SV> <20160512152805.GJ11226@e104818-lin.cambridge.arm.com> CC: , , , , , , , , , , , , , , , , , "Zhangjian (Bamvor)" , Kefeng Wang From: "Zhangjian (Bamvor)" Message-ID: <57358C2B.1010106@huawei.com> Date: Fri, 13 May 2016 16:11:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <20160512152805.GJ11226@e104818-lin.cambridge.arm.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.72.170] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020206.57358C3E.00A2,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: e999ea89e92442d7dec6c170c32535d5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 2016/5/12 23:28, Catalin Marinas wrote: > On Thu, May 12, 2016 at 05:24:57PM +0300, Yury Norov wrote: >> On Thu, May 12, 2016 at 03:07:35PM +0100, Catalin Marinas wrote: >>> On Thu, May 12, 2016 at 04:44:31PM +0300, Yury Norov wrote: >>>> On Thu, May 12, 2016 at 02:35:34PM +0100, Catalin Marinas wrote: >>>>> On Thu, May 12, 2016 at 03:20:00AM +0300, 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. >>> >>> [...] >>> >>>>>> --- a/arch/arm64/kernel/binfmt_elf32.c >>>>>> +++ b/arch/arm64/kernel/binfmt_elf32.c >>>>>> @@ -12,6 +12,7 @@ >>>>>> do { \ >>>>>> clear_thread_flag(TIF_32BIT_AARCH64); \ >>>>>> set_thread_flag(TIF_32BIT); \ >>>>>> + set_fs(TASK_SIZE_32); \ >>>>>> } while (0) >>>>>> >>>>>> #define COMPAT_ARCH_DLINFO >>>>>> diff --git a/arch/arm64/kernel/binfmt_ilp32.c b/arch/arm64/kernel/binfmt_ilp32.c >>>>>> index a934fd4..a8599c6 100644 >>>>>> --- a/arch/arm64/kernel/binfmt_ilp32.c >>>>>> +++ b/arch/arm64/kernel/binfmt_ilp32.c >>>>>> @@ -59,6 +59,7 @@ static void cputime_to_compat_timeval(const cputime_t cputime, >>>>>> do { \ >>>>>> set_thread_flag(TIF_32BIT_AARCH64); \ >>>>>> clear_thread_flag(TIF_32BIT); \ >>>>>> + set_fs(TASK_SIZE_32); \ >>>>>> } while (0) >>>>> >>>>> I don't think we need these two. AFAICT, flush_old_exec() takes care of >>>>> setting the USER_DS for the new thread. >>>> >>>> That's true, but USER_DS depends on personality which is not set yet >>>> for new thread, as I wrote above. In fact, I tried correct USER_DS >>>> only, and it doesn't work >>> >>> Ah, it looks like load_elf_binary() sets the personality after >>> flush_old_exec(). Looking at powerpc and x86, they set USER_DS to the >>> maximum 64-bit task value, so they should have a similar issue with >>> native 32-bit vs compat behaviour. >> >> Hmmm. If so, it means we'd introduce generic fix. It would be removing >> set_fs() from flush_old_exec() and appending it to load_elf_binary() >> after SET_PERSONALITY(). But I think it should be agreed with other >> arches developers. > > The set_fs() in flush_old_exec() is probably fine, it may be meant to > re-set the USER_DS for the old thread. > > It appears that at least powerpc and x86 don't have different USER_DS > setting for native and compat, so moving the set_fs() call further down > would not make any difference for them, nor will it fix the preadv02 LTP > test (if it fails for them, I haven't checked). > >> I've sent standalone patch for aarch64 (you in CC) so let's move >> discussion there. > > I've seen the patch but we would lose some discussion history here. I > think we should continue this thread and just summarise the conclusion > in reply to the other patch. This thread is also available on > linux-arch, in case other architecture maintainers follow it. > >>> So what exactly is LTP complaining about? Is different error (like >>> EFAULT vs EINVAL) or not getting an error at all. >> >> It should be EINVAL, but it succeed. The other problem is that >> following fs routines does not complain on wrong address. > > I see. The test asks the kernel to write a single byte (out of maximum > 64) to the user address 0xffffffff. What address We should set for this limitation, TASK_SIZE or STACK_TOP? It is same for 64bit application. But STACK_TOP(0xffff0000) is below TASK_SIZE in 32bit application. The address above STACK_TOP is preserved for 32bit application. Regards Bamvor > In the absence of the access_ok() > check, this operation succeeds. If the preadv syscall gets 2 bytes as > the count, then it would fail with EFAULT. > > While it's not really a bug, I agree that for matching the native 32-bit > behavior (basically for other syscalls like those involving vfs_read()), > the simplest fix would be to have a dynamic USER_DS. >