commit 6b12095a4a0e1f21bbf83f95f13299ca99d758fe
Author: Andi Kleen <ak@suse.de>
Date:   Wed Apr 12 08:19:29 2006 +0200

    [PATCH] x86_64: When user could have changed RIP always force IRET (CVE-2006-0744)
    
    Intel EM64T CPUs handle uncanonical return addresses differently from
    AMD CPUs.
    
    The exception is reported in the SYSRET, not the next instruction.
    Thgis leads to the kernel exception handler running on the user stack
    with the wrong GS because the kernel didn't expect exceptions on this
    instruction.
    
    This version of the patch has the teething problems that plagued an
    earlier version fixed.
    
    This is CVE-2006-0744
    
    Thanks to Ernie Petrides and Asit B. Mallick for analysis and initial
    patches.
    
    Signed-off-by: Andi Kleen <ak@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index 25dcb77..ab6e44d 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -180,6 +180,10 @@ rff_trace:
  *
  * XXX	if we had a free scratch register we could save the RSP into the stack frame
  *      and report it properly in ps. Unfortunately we haven't.
+ *
+ * When user can change the frames always force IRET. That is because
+ * it deals with uncanonical addresses better. SYSRET has trouble
+ * with them due to bugs in both AMD and Intel CPUs.
  */ 			 		
 
 ENTRY(system_call)
@@ -254,7 +258,10 @@ sysret_signal:
 	xorl %esi,%esi # oldset -> arg2
 	call ptregscall_common
 1:	movl $_TIF_NEED_RESCHED,%edi
-	jmp sysret_check
+	/* Use IRET because user could have changed frame. This
+	   works because ptregscall_common has called FIXUP_TOP_OF_STACK. */
+	cli
+	jmp int_with_check
 	
 badsys:
 	movq $-ENOSYS,RAX-ARGOFFSET(%rsp)
@@ -280,7 +287,8 @@ tracesys:
 	call syscall_trace_leave
 	RESTORE_TOP_OF_STACK %rbx
 	RESTORE_REST
-	jmp ret_from_sys_call
+	/* Use IRET because user could have changed frame */
+	jmp int_ret_from_sys_call
 	CFI_ENDPROC
 		
 /*