Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Merge x86 fixes from Ingo Molnar:
 "Two followup fixes related to the previous LDT fix"

Also applied a further FPU emulation fix from Andy Lutomirski to the
branch before actually merging it.

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
  x86/ldt: Further fix FPU emulation
  x86/ldt: Correct FPU emulation access to LDT
  x86/ldt: Correct LDT access in single stepping logic

arch/x86/kernel/step.c

@@ -28,11 +28,11 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re
 		struct desc_struct *desc;
 		unsigned long base;
 
-		seg &= ~7UL;
+		seg >>= 3;
 
 		mutex_lock(&child->mm->context.lock);
 		if (unlikely(!child->mm->context.ldt ||
-			     (seg >> 3) >= child->mm->context.ldt->size))
+			     seg >= child->mm->context.ldt->size))
 			addr = -1L; /* bogus selector, access would fault */
 		else {
 			desc = &child->mm->context.ldt->entries[seg];

arch/x86/math-emu/fpu_entry.c

@@ -29,7 +29,6 @@
 
 #include <asm/uaccess.h>
 #include <asm/traps.h>
-#include <asm/desc.h>
 #include <asm/user.h>
 #include <asm/fpu/internal.h>
 
@@ -181,7 +180,7 @@ void math_emulate(struct math_emu_info *info)
 			math_abort(FPU_info, SIGILL);
 		}
 
-		code_descriptor = LDT_DESCRIPTOR(FPU_CS);
+		code_descriptor = FPU_get_ldt_descriptor(FPU_CS);
 		if (SEG_D_SIZE(code_descriptor)) {
 			/* The above test may be wrong, the book is not clear */
 			/* Segmented 32 bit protected mode */

arch/x86/math-emu/fpu_system.h

@@ -16,9 +16,24 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 
-/* s is always from a cpu register, and the cpu does bounds checking
- * during register load --> no further bounds checks needed */
-#define LDT_DESCRIPTOR(s)	(((struct desc_struct *)current->mm->context.ldt)[(s) >> 3])
+#include <asm/desc.h>
+#include <asm/mmu_context.h>
+
+static inline struct desc_struct FPU_get_ldt_descriptor(unsigned seg)
+{
+	static struct desc_struct zero_desc;
+	struct desc_struct ret = zero_desc;
+
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+	seg >>= 3;
+	mutex_lock(&current->mm->context.lock);
+	if (current->mm->context.ldt && seg < current->mm->context.ldt->size)
+		ret = current->mm->context.ldt->entries[seg];
+	mutex_unlock(&current->mm->context.lock);
+#endif
+	return ret;
+}
+
 #define SEG_D_SIZE(x)		((x).b & (3 << 21))
 #define SEG_G_BIT(x)		((x).b & (1 << 23))
 #define SEG_GRANULARITY(x)	(((x).b & (1 << 23)) ? 4096 : 1)

arch/x86/math-emu/get_address.c

@@ -20,7 +20,6 @@
 #include <linux/stddef.h>
 
 #include <asm/uaccess.h>
-#include <asm/desc.h>
 
 #include "fpu_system.h"
 #include "exception.h"
@@ -158,7 +157,7 @@ static long pm_address(u_char FPU_modrm, u_char segment,
 		addr->selector = PM_REG_(segment);
 	}
 
-	descriptor = LDT_DESCRIPTOR(PM_REG_(segment));
+	descriptor = FPU_get_ldt_descriptor(addr->selector);
 	base_address = SEG_BASE_ADDR(descriptor);
 	address = base_address + offset;
 	limit = base_address