On Tue, May 05, 2015 at 06:19:24PM +0100, André Hentschel wrote: > Am 05.05.2015 um 19:15 schrieb Will Deacon: > > On Tue, May 05, 2015 at 06:09:57PM +0100, André Hentschel wrote: > >> Am 05.05.2015 um 12:51 schrieb Will Deacon: > >>> On Sun, May 03, 2015 at 05:24:18PM +0100, André Hentschel wrote: > >>> Curious, but why do you need this? iirc, we added this for arch/arm/ because > >>> of some windows rt (?) emulation in wine. Is that still the case here and is > >>> anybody actually using that? > >> > >> Yes, Windows ARM binaries are the well known use case, but also the compat > >> mode should do what the arm kernel is doing I’d think and the code wasn't > >> adjusted yet. > > > > Sure, I was just curious. > > OK :) > So what about the patch? I'll need to take a proper look (it's on the list). > >> What i'm curious about is why the main TLS register on arm64 is the user > >> writeable, I'm not an security expert but this looks odd. I could easily > >> provoke a crash by writing to it... > > > > You've probably got the wrong TLS. Allowing a program to clobber it's own > > thread-local storage is no worse than allowing it to write to its general > > purpose registers, pc, etc. > > > > I'm assuming the crash you saw was just a userspace crash, rather than > > the kernel? > > > > True, but the system became horribly instable, files were overwritten by > others, very strange. It was in a remote KVM VM on bare metal aarch64... > I don't dare to try it again because it causes others some trouble, but if > someone wants to try it out: https://github.com/AndreRH/tpidrurw-test Seems fine to me running both as 32-bit and 64-bit binary under an arm64 4.1-rc2 kernel. The former just has test failures (because we don't context switch the TLS): [...] ERROR: TPIDRURW is 00000000, expected cafebabe [...] whilst the latter SEGVs: tpidrurw-test[1691]: unhandled level 1 translation fault (11) at 0xdeadbac2, esr 0x92000005 pgd = ffffffc079079000 [deadbac2] *pgd=0000000000000000, *pud=0000000000000000 [...] Will -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
