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From cd0c80aa02dbfe649c743fa98fcc0d9f427e0827 Mon Sep 17 00:00:00 2001
Message-Id: <cd0c80aa02dbfe649c743fa98fcc0d9f427e0827.1518828081.git.jan.steffens@gmail.com>
In-Reply-To: <05a43fb8b36cdaf6a3580f46cab334f2c2796544.1518828081.git.jan.steffens@gmail.com>
References: <05a43fb8b36cdaf6a3580f46cab334f2c2796544.1518828081.git.jan.steffens@gmail.com>
From: Juergen Gross <jgross@suse.com>
Date: Thu, 1 Feb 2018 13:40:19 +0100
Subject: [PATCH 3/3] x86/xen: init %gs very early to avoid page faults with
stack protector
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>
---
arch/x86/xen/xen-head.S | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 497cc55a0c16..96f26e026783 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -9,32 +9,48 @@
#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>
#include <xen/interface/features.h>
#include <xen/interface/xen.h>
#include <xen/interface/xen-mca.h>
#include <asm/xen/interface.h>
#ifdef CONFIG_XEN_PV
__INIT
ENTRY(startup_xen)
UNWIND_HINT_EMPTY
cld
/* Clear .bss */
xor %eax,%eax
mov $__bss_start, %_ASM_DI
mov $__bss_stop, %_ASM_CX
sub %_ASM_DI, %_ASM_CX
shr $__ASM_SEL(2, 3), %_ASM_CX
rep __ASM_SIZE(stos)
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
--
2.16.1
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