Patch "x86/xen: init %gs very early to avoid page faults with stack protector" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    x86/xen: init %gs very early to avoid page faults with stack protector

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-xen-init-gs-very-early-to-avoid-page-faults-with-stack-protector.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 4f277295e54c5b7340e48efea3fc5cc21a2872b7 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Thu, 1 Feb 2018 13:40:19 +0100
Subject: x86/xen: init %gs very early to avoid page faults with stack protector

From: Juergen Gross <jgross@suse.com>

commit 4f277295e54c5b7340e48efea3fc5cc21a2872b7 upstream.

When running as Xen pv guest %gs is initialized some time after
C code is started. Depending on stack protector usage this might be
too late, resulting in page faults.

So setup %gs and MSR_GS_BASE in assembly code already.

Cc: stable@vger.kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: Chris Patterson <cjp256@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/xen/xen-head.S |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -9,7 +9,9 @@
 
 #include <asm/boot.h>
 #include <asm/asm.h>
+#include <asm/msr.h>
 #include <asm/page_types.h>
+#include <asm/percpu.h>
 #include <asm/unwind_hints.h>
 
 #include <xen/interface/elfnote.h>
@@ -35,6 +37,20 @@ ENTRY(startup_xen)
 	mov %_ASM_SI, xen_start_info
 	mov $init_thread_union+THREAD_SIZE, %_ASM_SP
 
+#ifdef CONFIG_X86_64
+	/* Set up %gs.
+	 *
+	 * The base of %gs always points to the bottom of the irqstack
+	 * union.  If the stack protector canary is enabled, it is
+	 * located at %gs:40.  Note that, on SMP, the boot cpu uses
+	 * init data section till per cpu areas are set up.
+	 */
+	movl	$MSR_GS_BASE,%ecx
+	movq	$INIT_PER_CPU_VAR(irq_stack_union),%rax
+	cdq
+	wrmsr
+#endif
+
 	jmp xen_start_kernel
 END(startup_xen)
 	__FINIT


Patches currently in stable-queue which might be from jgross@suse.com are

queue-4.15/x86-xen-init-gs-very-early-to-avoid-page-faults-with-stack-protector.patch