From a5b9e5a2f14f25a8dae987494d50ad3aac7366b6 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Thu, 30 Jul 2015 14:31:34 -0700
Subject: x86/ldt: Make modify_ldt() optional

The modify_ldt syscall exposes a large attack surface and is
unnecessary for modern userspace.  Make it optional.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: security@kernel.org <security@kernel.org>
Cc: xen-devel <xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/a605166a771c343fd64802dece77a903507333bd.1438291540.git.luto@kernel.org
[ Made MATH_EMULATION dependent on MODIFY_LDT_SYSCALL. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/process_64.c | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'arch/x86/kernel/process_64.c')

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7ff035c6c54d..3c1bbcf12924 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -121,6 +121,7 @@ void __show_regs(struct pt_regs *regs, int all)
 void release_thread(struct task_struct *dead_task)
 {
 	if (dead_task->mm) {
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
 		if (dead_task->mm->context.ldt) {
 			pr_warn("WARNING: dead process %s still has LDT? <%p/%d>\n",
 				dead_task->comm,
@@ -128,6 +129,7 @@ void release_thread(struct task_struct *dead_task)
 				dead_task->mm->context.ldt->size);
 			BUG();
 		}
+#endif
 	}
 }
 
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