From: Eugene Teo <eteo@redhat.com>
Date: Wed, 6 Aug 2008 13:03:12 +0800
Subject: [x86_64] xen: local DOS due to NT bit leakage
Message-id: 20080806050312.GA20735@kernel.sg
O-Subject: [RHEL5.3 PATCH] kernel: local denial of service due to NT bit leakage v2
Bugzilla: 457722
RH-Acked-by: Chuck Ebbert <cebbert@redhat.com>
RH-Acked-by: Jiri Pirko <jpirko@redhat.com>
CVE: CVE-2006-5755

Second try.

This is for bz#457722 (CVE-2006-5755).

Backport of commit 658fdbef66e5e9be79b457edc2cbbb3add840aa9

SYSENTER can cause a NT to be set which might cause crashes on the IRET
in the next task.

This patch ensures that -xen is patched, and not forgotten.

Brew build:
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1422417

Signed-off-by: Eugene Teo <eteo@redhat.com>

diff --git a/arch/x86_64/kernel/entry-xen.S b/arch/x86_64/kernel/entry-xen.S
index c6f2a23..37e1708 100644
--- a/arch/x86_64/kernel/entry-xen.S
+++ b/arch/x86_64/kernel/entry-xen.S
@@ -187,6 +187,10 @@ NMI_MASK = 0x80000000
 /* rdi:	prev */	
 ENTRY(ret_from_fork)
 	CFI_DEFAULT_STACK
+	push kernel_eflags(%rip)
+	CFI_ADJUST_CFA_OFFSET 4
+	popf                # reset kernel eflags
+	CFI_ADJUST_CFA_OFFSET -4
 	call schedule_tail
 	GET_THREAD_INFO(%rcx)
 	testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),threadinfo_flags(%rcx)
diff --git a/arch/x86_64/kernel/setup64-xen.c b/arch/x86_64/kernel/setup64-xen.c
index 36f486e..d4e813d 100644
--- a/arch/x86_64/kernel/setup64-xen.c
+++ b/arch/x86_64/kernel/setup64-xen.c
@@ -213,6 +213,8 @@ void __cpuinit check_efer(void)
         }       
 }
 
+unsigned long kernel_eflags;
+
 /*
  * cpu_init() initializes state that is per-CPU. Some data is already
  * initialized (naturally) in the bootstrap process, such as the GDT
@@ -336,4 +338,6 @@ void __cpuinit cpu_init (void)
 	set_debugreg(0UL, 7);
 
 	fpu_init(); 
+
+	raw_local_save_flags(kernel_eflags);
 }
diff --git a/include/asm-x86_64/mach-xen/asm/system.h b/include/asm-x86_64/mach-xen/asm/system.h
index 7d8b882..69df8a4 100644
--- a/include/asm-x86_64/mach-xen/asm/system.h
+++ b/include/asm-x86_64/mach-xen/asm/system.h
@@ -22,12 +22,13 @@
 #define __RESTORE(reg,offset) "movq (14-" #offset ")*8(%%rsp),%%" #reg "\n\t"
 
 /* frame pointer must be last for get_wchan */
-#define SAVE_CONTEXT    "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
-#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\n\t"
+#define SAVE_CONTEXT    "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
+#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
 
 #define __EXTRA_CLOBBER  \
 	,"rcx","rbx","rdx","r8","r9","r10","r11","r12","r13","r14","r15"
 
+/* Save restore flags to clear handle leaking NT */
 #define switch_to(prev,next,last) \
 	asm volatile(SAVE_CONTEXT						    \
 		     "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */	  \