1 files changed, 56 insertions, 0 deletions
diff --git a/main/linux-grsec/xsa40.patch b/main/linux-grsec/xsa40.patch
new file mode 100644
index 000000000..29db917cb
--- /dev/null
+++ b/main/linux-grsec/xsa40.patch
@@ -0,0 +1,56 @@
+Xen: Fix stack corruption in xen_failsafe_callback for 32bit PVOPS guests.
+
+This fixes CVE-2013-0190 / XSA-40
+
+There has been an error on the xen_failsafe_callback path for failed
+iret, which causes the stack pointer to be wrong when entering the
+iret_exc error path.  This can result in the kernel crashing.
+
+In the classic kernel case, the relevant code looked a little like:
+
+        popl %eax      # Error code from hypervisor
+        jz 5f
+        addl $16,%esp
+        jmp iret_exc   # Hypervisor said iret fault
+5:      addl $16,%esp
+                       # Hypervisor said segment selector fault
+
+Here, there are two identical addls on either option of a branch which
+appears to have been optimised by hoisting it above the jz, and
+converting it to an lea, which leaves the flags register unaffected.
+
+In the PVOPS case, the code looks like:
+
+        popl_cfi %eax         # Error from the hypervisor
+        lea 16(%esp),%esp     # Add $16 before choosing fault path
+        CFI_ADJUST_CFA_OFFSET -16
+        jz 5f
+        addl $16,%esp         # Incorrectly adjust %esp again
+        jmp iret_exc
+
+It is possible unprivileged userspace applications to cause this
+behaviour, for example by loading an LDT code selector, then changing
+the code selector to be not-present.  At this point, there is a race
+condition where it is possible for the hypervisor to return back to
+userspace from an interrupt, fault on its own iret, and inject a
+failsafe_callback into the kernel.
+
+This bug has been present since the introduction of Xen PVOPS support
+in commit 5ead97c84 (xen: Core Xen implementation), in 2.6.23.
+
+Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
+Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
+
+diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
+index ff84d54..6ed91d9 100644
+--- a/arch/x86/kernel/entry_32.S
++++ b/arch/x86/kernel/entry_32.S
+@@ -1065,7 +1065,6 @@ ENTRY(xen_failsafe_callback)
+ 	lea 16(%esp),%esp
+ 	CFI_ADJUST_CFA_OFFSET -16
+ 	jz 5f
+-	addl $16,%esp
+ 	jmp iret_exc
+ 5:	pushl_cfi $-1 /* orig_ax = -1 => not a system call */
+ 	SAVE_ALL
+