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Commit 4f277295 authored by Juergen Gross's avatar Juergen Gross
Browse files

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: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: default avatarChris Patterson <cjp256@gmail.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent ddb9e13a

arch/x86/xen/xen-head.S

+16 −0
Original line number Diff line number Diff line
@@ -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