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@xxxxxxxxxxxxxxx> know about it.
>From 4f277295e54c5b7340e48efea3fc5cc21a2872b7 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@xxxxxxxx>
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@xxxxxxxx>
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@xxxxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Tested-by: Chris Patterson <cjp256@xxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxx are
queue-4.15/x86-xen-init-gs-very-early-to-avoid-page-faults-with-stack-protector.patch