From 36104cb9012a82e73c32a3b709257766b16bcd1d Mon Sep 17 00:00:00 2001 From: Jason Andryuk Date: Mon, 19 Mar 2018 12:58:04 -0400 Subject: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") introduced a call to get_cpu_cap, which is fstack-protected. This is works on x86-64 as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page faults with stack protector") ensures the stack protector is configured, but it it did not cover x86-32. Delay calling get_cpu_cap until after xen_setup_gdt has initialized the stack canary. Without this, a 32bit PV machine crashes early in boot. (XEN) Domain 0 (vcpu#0) crashed on cpu#0: (XEN) ----[ Xen-4.6.6-xc x86_64 debug=n Tainted: C ]---- (XEN) CPU: 0 (XEN) RIP: e019:[<00000000c10362f8>] And the PV kernel IP corresponds to init_scattered_cpuid_features 0xc10362f8 <+24>: mov %gs:0x14,%eax Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") Signed-off-by: Jason Andryuk Reviewed-by: Boris Ostrovsky Signed-off-by: Boris Ostrovsky --- arch/x86/xen/enlighten_pv.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 3c2c2530737e..c36d23aa6c35 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -1259,10 +1259,6 @@ asmlinkage __visible void __init xen_start_kernel(void) */ __userpte_alloc_gfp &= ~__GFP_HIGHMEM; - /* Work out if we support NX */ - get_cpu_cap(&boot_cpu_data); - x86_configure_nx(); - /* Get mfn list */ xen_build_dynamic_phys_to_machine(); @@ -1272,6 +1268,10 @@ asmlinkage __visible void __init xen_start_kernel(void) */ xen_setup_gdt(0); + /* Work out if we support NX */ + get_cpu_cap(&boot_cpu_data); + x86_configure_nx(); + xen_init_irq_ops(); /* Let's presume PV guests always boot on vCPU with id 0. */ -- 2.30.2