From 782e9c805d19610d5821d1f75a3854ac587e2dac Mon Sep 17 00:00:00 2001 Message-Id: <782e9c805d19610d5821d1f75a3854ac587e2dac.1518653356.git.jan.steffens@gmail.com> In-Reply-To: <44c5097b2711429f0d49d138681f67157982e729.1518653356.git.jan.steffens@gmail.com> References: <44c5097b2711429f0d49d138681f67157982e729.1518653356.git.jan.steffens@gmail.com> From: Juergen Gross Date: Thu, 1 Feb 2018 13:40:19 +0100 Subject: [PATCH 4/4] 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 Reviewed-by: Boris Ostrovsky Tested-by: Chris Patterson Signed-off-by: Juergen Gross --- 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 #include +#include #include +#include #include #include #include #include #include #include #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