Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 18 Sep 2020 17:11:50 -0700 | Subject | Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled |
| |
On Fri, Sep 18, 2020 at 12:23 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > > Emulation of the legacy vsyscall page is required by some programs > built before 2013. Newer programs after 2013 don't use it. > Disable vsyscall emulation when Control-flow Enforcement (CET) is > enabled to enhance security. > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > --- > v12: > - Disable vsyscall emulation only when it is attempted (vs. at compile time). > > arch/x86/entry/vsyscall/vsyscall_64.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c > index 44c33103a955..3196e963e365 100644 > --- a/arch/x86/entry/vsyscall/vsyscall_64.c > +++ b/arch/x86/entry/vsyscall/vsyscall_64.c > @@ -150,6 +150,15 @@ bool emulate_vsyscall(unsigned long error_code, > > WARN_ON_ONCE(address != regs->ip); > > +#ifdef CONFIG_X86_INTEL_CET > + if (current->thread.cet.shstk_size || > + current->thread.cet.ibt_enabled) { > + warn_bad_vsyscall(KERN_INFO, regs, > + "vsyscall attempted with cet enabled"); > + return false; > + }
Nope, try again. Having IBT on does *not* mean that every library in the process knows that we have indirect branch tracking. The legacy bitmap exists for a reason. Also, I want a way to flag programs as not using the vsyscall page, but that flag should not be called CET. And a process with vsyscalls off should not be able to read the vsyscall page, and /proc/self/maps should be correct.
So you have some choices:
1. Drop this patch and make it work.
2. Add a real per-process vsyscall control. Either make it depend on vsyscall=xonly and wire it up correctly or actually make it work correctly with vsyscall=emulate.
NAK to any hacks in this space. Do it right or don't do it at all.
| |