| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 038/167] x86/xen: init %gs very early to avoid page faults with stack protector | Date | Wed, 21 Feb 2018 13:47:29 +0100 |
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4.14-stable review patch. If anyone has any objections, please let me know.
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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
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