x86/vsyscall/64: Warn and fail vsyscall emulation in NATIVE mode

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 <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index daad57c76e42..1faf40f2dda9 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -139,6 +139,10 @@ 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");