x86/ldt: Correct LDT access in single stepping logic

commit 136d9d83c07c5e30ac49fc83b27e8c4842f108fc upstream.

Commit 37868fe113ff ("x86/ldt: Make modify_ldt synchronous")
introduced a new struct ldt_struct anchored at mm->context.ldt.

convert_ip_to_linear() was changed to reflect this, but indexing
into the ldt has to be changed as the pointer is no longer void *.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/1438848278-12906-1-git-send-email-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index b54e52d..bfe6a14 100644 (file)
--- 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];