[PATCH 4.1 002/102] x86/ldt: Correct LDT access in single stepping logic

From: Greg Kroah-Hartman
Date: Sat Sep 19 2015 - 14:28:56 EST


4.1-stable review patch. If anyone has any objections, please let me know.

------------------

From: Juergen Gross <jgross@xxxxxxxx>

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@xxxxxxxx>
Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bp@xxxxxxx
Link: http://lkml.kernel.org/r/1438848278-12906-1-git-send-email-jgross@xxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
arch/x86/kernel/step.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -28,11 +28,11 @@ unsigned long convert_ip_to_linear(struc
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];


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