On Thu, May 12, 2022 at 09:21:13AM +0200, Arnd Bergmann wrote: > On Wed, May 11, 2022 at 11:12 PM Rich Felker <dalias@xxxxxxxx> wrote: > > On Wed, May 11, 2022 at 09:11:56AM +0200, Arnd Bergmann wrote: > > > On Mon, May 9, 2022 at 12:00 PM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > ..... > > > > I can try and move a poc for this up the todo list. > > > > > > > > Without an approach like this certain sandboxes will fallback to > > > > ENOSYSing system calls they can't filter. This is a generic problem > > > > though with clone3() being one promiment example. > > > > > > Thank you for the detailed reply. It sounds to me like this will eventually have > > > to get solved anyway, so we could move ahead without clone() on loongarch, > > > and just not have support for Chrome until this is fully solved. > > > > > > As both the glibc and musl ports are being proposed for inclusion right > > > now, we should try to come to a decision so the libc ports can adjust if > > > necessary. Adding both mailing lists to Cc here, the discussion is archived > > > at [1]. > > > > > > Arnd > > > > > > [1] https://lore.kernel.org/linux-arch/20220509100058.vmrgn5fkk3ayt63v@wittgenstein/ > > > > Having read about the seccomp issue, I think it's a very strong > > argument that __NR_clone should be kept permanently for all future > > archs. > > Ok, let's keep clone() around for all architectures then. We should probably > just remove the __ARCH_WANT_SYS_CLONE macro and build the > code into the kernel unconditionally, but at the moment there > are still private versions for ia64 and sparc with the same name as > the generic version. Both are also still lacking support for clone3() and > don't have anyone actively working on them. > > In this case, we probably don't need to change clone3() to allow the > zero-length stack after all, and the wrapper that was added to the > musl port should get removed again. I still think disallowing a zero length (unknown length with caller providing the start address only) stack is a gratuitous limitation on the clone3 interface, and would welcome leaving the change to allow zero-length in place. There does not seem to be any good justification for forbidding it, and it does pose other real-world obstruction to use. For example if your main thread had exited (or if you're forking from a non-main thread) and you wanted to create a new process using the old main thread stack as your stack, you would not know a size/lowest-address, only a starting address from which it extends some long (and possibly expanding) amount. Rich
