From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [RFC6 PATCH v6 00/21] ILP32 for ARM64 Date: Thu, 12 May 2016 16:28:06 +0100 Message-ID: <20160512152805.GJ11226@e104818-lin.cambridge.arm.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from foss.arm.com ([217.140.101.70]:59661 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932211AbcELP2N (ORCPT ); Thu, 12 May 2016 11:28:13 -0400 Content-Disposition: inline In-Reply-To: <20160512142457.GC30205@yury-N73SV> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yury Norov Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, arnd@arndb.de, pinskia@gmail.com, Prasun.Kapoor@caviumnetworks.com, heiko.carstens@de.ibm.com, linux-doc@vger.kernel.org, Nathan_Lynch@mentor.com, linux-kernel@vger.kernel.org, agraf@suse.de, klimov.linux@gmail.com, broonie@kernel.org, bamvor.zhangjian@huawei.com, linux-arm-kernel@lists.infradead.org, schwab@suse.de, schwidefsky@de.ibm.com, joseph@codesourcery.com, christoph.muellner@theobroma-systems.com 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. 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. -- Catalin