On Wed, Nov 1, 2017 at 3:20 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Wed, 1 Nov 2017, Linus Torvalds wrote: >> On Wed, Nov 1, 2017 at 2:52 PM, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: >> > On 11/01/2017 02:28 PM, Thomas Gleixner wrote: >> >> On Wed, 1 Nov 2017, Andy Lutomirski wrote: >> >>> The vsyscall page is _PAGE_USER and lives in init_mm via the fixmap. >> >> >> >> Groan, forgot about that abomination, but still there is no point in having >> >> it marked PAGE_USER in the init_mm at all, kaiser or not. >> > >> > So shouldn't this patch effectively make the vsyscall page unusable? >> > Any idea why that didn't show up in any of the x86 selftests? >> >> I actually think there may be two issues here: >> >> - vsyscall isn't even used much - if any - any more > > Only legacy user space uses it. > >> - the vsyscall emulation works fine without _PAGE_USER, since the >> whole point is that we take a fault on it and then emulate. >> >> We do expose the vsyscall page read-only to user space in the >> emulation case, but I'm not convinced that's even required. > > I don't see a reason why it needs to be mapped at all for emulation. > >> Nobody who configures KAISER enabled would possibly want to have the >> actual native vsyscall page enabled. That would be an insane >> combination. >> >> So the only possibly difference would be a user mode program that >> actually looks at the vsyscall page, which sounds unlikely to be an >> issue. It's legacy and not really used. > > Right, and we can either disable the NATIVE mode when KAISER is on or just > rip the native mode out completely. Most distros have native mode disabled > anyway, so you cannot even enable it on the kernel command line. > > I'm all for ripping it out or at least removing the config switch to enable > native mode as a first step. I would like to see NATIVE removed too. -Kees -- Kees Cook Pixel Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
