[PATCH PTI v3 06/10] x86/vsyscall/64: Warn and fail vsyscall emulation in NATIVE mode

[Andy Lutomirski]

If something goes wrong with pagetable setup, vsyscall=native will
accidentally fall back to emulation.  Make it warn and fail so that
we notice.

Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
 arch/x86/entry/vsyscall/vsyscall_64.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c 
b/arch/x86/entry/vsyscall/vsyscall_64.c
index bc88a0540347..a06f2ae09ad6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -138,6 +138,10 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long 
address)
 
        WARN_ON_ONCE(address != regs->ip);
 
+       /* This should be unreachable in NATIVE mode. */
+       if (WARN_ON(vsyscall_mode == NATIVE))
+               return false;
+
        if (vsyscall_mode == NONE) {
                warn_bad_vsyscall(KERN_INFO, regs,
                                  "vsyscall attempted with vsyscall=none");
-- 
2.13.6