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x86/xen: Delay get_cpu_cap until stack canary is established 

Commit 2cc42bac1c ("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 4f277295e5 ("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 2cc42bac1c ("x86-64/Xen: eliminate W+X mappings")

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
This commit is contained in:
Jason Andryuk 2018-03-19 12:58:04 -04:00 committed by Boris Ostrovsky
parent 8fe5ab4112
commit 36104cb901
1 changed files with 4 additions and 4 deletions
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8
arch/x86/xen/enlighten_pv.c
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@ -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. */