On 11/10/2017 02:06 PM, Andy Lutomirski wrote: > On Thu, Nov 9, 2017 at 10:31 PM, Dave Hansen > <[email protected]> wrote: >> On 11/09/2017 06:25 PM, Andy Lutomirski wrote: >>> Here are two proposals to address this without breaking vsyscalls. >>> >>> 1. Set NX on low mappings that are _PAGE_USER. Don't set NX on high >>> mappings but, optionally, warn if you see _PAGE_USER on any address >>> that isn't the vsyscall page. >>> >>> 2. Ignore _PAGE_USER entirely and just mark the EFI mm as special so >>> KAISER doesn't muck with it. >> >> These are totally doable. But, what's the big deal with breaking native >> vsyscall? We can still do the emulation so nothing breaks: it is just slow. > > I have nothing against disabling native. I object to breaking the > weird binary tracing behavior in the emulation mode, especially if > it's tangled up with KAISER. I got all kinds of flak in an earlier > version of the vsyscall emulation patches when I broke that use case. > KAISER may get very widely backported -- let's not make changes that > are already known to break things.
Is the thing that broke a "user mode program that actually looks at the vsyscall page"? Like Linus is referring to here: > http://lkml.kernel.org/r/ca+55afyijhb4wndmkgexektzhyt8pajqsau2peo3o4ekizb...@mail.gmail.com
