On 03/19/2018 12:58 PM, Jason Andryuk wrote:
> 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 <[email protected]>
>
Applied to for-linus-4.17
-boris
