From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940736AbdDTDyl (ORCPT ); Wed, 19 Apr 2017 23:54:41 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:5447 "EHLO dggrg03-dlp.huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S937582AbdDTDyd (ORCPT ); Wed, 19 Apr 2017 23:54:33 -0400 Subject: Re: [PATCH] fs: Preventing READ_IMPLIES_EXEC Propagation To: Catalin Marinas , Peter Maydell , References: <1492088223-98232-1-git-send-email-zhangshaokun@hisilicon.com> <2414e3b3-03f6-bd6c-5aa4-ad58c66b5aa5@huawei.com> <20170418170118.GH27592@e104818-lin.cambridge.arm.com> <20170419103313.GA3238@e104818-lin.cambridge.arm.com> CC: Mark Rutland , Peter Maydell , Will Deacon , Linuxarm , "linux-kernel@vger.kernel.org" , Al Viro , , arm-mail-list , From: "dongbo (E)" Message-ID: Date: Thu, 20 Apr 2017 11:50:38 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20170419103313.GA3238@e104818-lin.cambridge.arm.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.63.194.120] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A010204.58F8301C.0005,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: df5153f1fb48a6f711e4c11891e18821 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/4/19 18:33, Catalin Marinas wrote: > On Tue, Apr 18, 2017 at 09:01:52PM +0100, Peter Maydell wrote: >> On 18 April 2017 at 18:01, Catalin Marinas wrote: >>> On Thu, Apr 13, 2017 at 08:33:52PM +0800, dongbo (E) wrote: >>>> From: Dong Bo >>>> >>>> In load_elf_binary(), once the READ_IMPLIES_EXEC flag is set, >>>> the flag is propagated to its child processes, even the elf >>>> files are marked as not requiring executable stack. It may >>>> cause superfluous operations on some arch, e.g. >>>> __sync_icache_dcache on aarch64 due to a PROT_READ mmap is >>>> also marked as PROT_EXEC. >>>> >>>> Signed-off-by: Dong Bo >>>> --- >>>> fs/binfmt_elf.c | 2 ++ >>>> fs/binfmt_elf_fdpic.c | 2 ++ >>>> 2 files changed, 4 insertions(+) >>>> >>>> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c >>>> index 5075fd5..c52e670 100644 >>>> --- a/fs/binfmt_elf.c >>>> +++ b/fs/binfmt_elf.c >>>> @@ -863,6 +863,8 @@ static int load_elf_binary(struct linux_binprm *bprm) >>>> SET_PERSONALITY2(loc->elf_ex, &arch_state); >>>> if (elf_read_implies_exec(loc->elf_ex, executable_stack)) >>>> current->personality |= READ_IMPLIES_EXEC; >>>> + else >>>> + current->personality &= ~READ_IMPLIES_EXEC; >>>> if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space) >>>> current->flags |= PF_RANDOMIZE; >>>> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c >>>> index cf93a4f..c4bc4d0 100644 >>>> --- a/fs/binfmt_elf_fdpic.c >>>> +++ b/fs/binfmt_elf_fdpic.c >>>> @@ -354,6 +354,8 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm) >>>> set_personality(PER_LINUX); >>>> if (elf_read_implies_exec(&exec_params.hdr, executable_stack)) >>>> current->personality |= READ_IMPLIES_EXEC; >>>> + else >>>> + current->personality &= ~READ_IMPLIES_EXEC; >>>> setup_new_exec(bprm); >> >>> That's affecting most architectures with a risk of ABI breakage. We >>> could do it on arm64 only, though I'm not yet clear on the ABI >>> implications (at a first look, there shouldn't be any). >> >> Is there a reason why it isn't just straightforwardly a bug >> (which we could fix) to make READ_IMPLIES_EXEC propagate to >> child processes? > > While I agree that it looks like a bug, if there are user programs > relying on such bug we call it "ABI". On arm64, I don't think there is > anything relying on inheriting READ_IMPLIES_EXEC but I wouldn't change > the compat task handling without the corresponding change in arch/arm. > With READ_IMPLIES_EXEC propagation, several hundreds times of __sync_icache_dcache operations shows up than not READ_IMPLIES_EXEC propagation, which degenerating the system performance. Changing arm64 only would settle our problem down, thanks for figuring out previously. Seems that arch/arm had discussed the propagation of READ_IMPLIES_EXEC: http://lists.infradead.org/pipermail/linux-arm-kernel/2012-February/086490.html But the READ_IMPLIES_EXEC is still not cleared in elf_set_personality(). >> AFAICT this should be per-process: just because >> init happens not to have been (re)compiled to permit non-executable >> stacks doesn't mean every process on the system needs to have >> an executable stack. > > I think this also affects the heap if brk(2) is used (via > VM_DATA_DEFAULT_FLAGS though I guess malloc mostly uses mmap these > days). > >> Behaviour shouldn't be variable across architectures either, I would >> hope. > > The behaviour has already been variable for a long time. Even on x86, > AFAICT x86_32 differs from x86_64 in this respect. > > Anyway, the patch should be posted to linux-arch for a cross-arch > discussion. > OK, this mail Cc to linux-arch. Thanks.