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

4 files changed, 22 insertions, 9 deletions

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 6273324186ac..0ccb53a9fcd9 100644
--- a/arch/x86/kernel/step.c
+++ b/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];
diff --git a/arch/x86/math-emu/fpu_entry.c b/arch/x86/math-emu/fpu_entry.c
index f37e84ab49f3..3d8f2e421466 100644
--- a/arch/x86/math-emu/fpu_entry.c
+++ b/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 */
diff --git a/arch/x86/math-emu/fpu_system.h b/arch/x86/math-emu/fpu_system.h
index 9ccecb61a4fa..5e044d506b7a 100644
--- a/arch/x86/math-emu/fpu_system.h
+++ b/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)
diff --git a/arch/x86/math-emu/get_address.c b/arch/x86/math-emu/get_address.c
index 6ef5e99380f9..8300db71c2a6 100644
--- a/arch/x86/math-emu/get_address.c
+++ b/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