[tip:x86/entry] x86/vsyscall: Change the default vsyscall mode to xonly

[tip-bot for Andy Lutomirski]

Commit-ID:  625b7b7f79c66626fb2b7687fc1a58309a57edd5
Gitweb:     https://git.kernel.org/tip/625b7b7f79c66626fb2b7687fc1a58309a57edd5
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Wed, 26 Jun 2019 21:45:07 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200

x86/vsyscall: Change the default vsyscall mode to xonly

The use case for full emulation over xonly is very esoteric, e.g. magic
instrumentation tools.

Change the default to the safer xonly mode.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Florian Weimer <fweimer@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/30539f8072d2376b9c9efcc07e6ed0d6bf20e882.1561610354.git.luto@xxxxxxxxxx

---
 arch/x86/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0182d2c67590..32028edc1b0e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2285,7 +2285,7 @@ config COMPAT_VDSO
 choice
 	prompt "vsyscall table for legacy applications"
 	depends on X86_64
-	default LEGACY_VSYSCALL_EMULATE
+	default LEGACY_VSYSCALL_XONLY
 	help
 	  Legacy user code that does not know how to find the vDSO expects
 	  to be able to issue three syscalls by calling fixed addresses in