x86-64, modify_ldt: Make support for 16-bit segments a runtime option

[karo-tx-linux.git] / arch / x86 / kernel / ldt.c

diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index ebc9873989233dcba13d1fa1af14e3e921959a85..dcbbaa165bdeed61dd2b504a13ca05ced99737c7 100644 (file)
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -20,6 +20,8 @@
 #include <asm/mmu_context.h>
 #include <asm/syscalls.h>
 
+int sysctl_ldt16 = 0;
+
 #ifdef CONFIG_SMP
 static void flush_ldt(void *current_mm)
 {
@@ -229,6 +231,17 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
                }
        }
 
+       /*
+        * On x86-64 we do not support 16-bit segments due to
+        * IRET leaking the high bits of the kernel stack address.
+        */
+#ifdef CONFIG_X86_64
+       if (!ldt_info.seg_32bit && !sysctl_ldt16) {
+               error = -EINVAL;
+               goto out_unlock;
+       }
+#endif
+
        fill_ldt(&ldt, &ldt_info);
        if (oldmode)
                ldt.avl = 0;