From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Wed, 19 Apr 2017 11:33:14 +0100 Subject: [PATCH] fs: Preventing READ_IMPLIES_EXEC Propagation In-Reply-To: References: <1492088223-98232-1-git-send-email-zhangshaokun@hisilicon.com> <2414e3b3-03f6-bd6c-5aa4-ad58c66b5aa5@huawei.com> <20170418170118.GH27592@e104818-lin.cambridge.arm.com> Message-ID: <20170419103313.GA3238@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. > > > 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. > 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. -- Catalin