On Wed, Apr 19, 2017 at 11:33:14AM +0100, 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 <catalin.marinas@xxxxxxx> wrote: > > > On Thu, Apr 13, 2017 at 08:33:52PM +0800, dongbo (E) wrote: > > >> From: Dong Bo <dongbo4@xxxxxxxxxx> > > >> > > >> 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). I think it also affects mprotect, which is more worrying imo, particularly for things like JIT code that is ported from 32-bit (although a quick look at v8, ionmonkey and art suggests they all pass PROT_EXEC when needed). Will
