Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Boris Ostrovsky]

On 03/31/2018 01:38 PM, Jason Andryuk wrote:
> On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky 
> <boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote:
>
>     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:Â Â 0
>      > (XEN) RIP:Â Â 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 <jandryuk@xxxxxxxxx
>     <mailto:jandryuk@xxxxxxxxx>>
>      >
>
>
>     Applied to for-linus-4.17
>
>
> Thanks. If it's not too late, can this be cc: stable? 


We can always try ;-)

This is 4.15 and 4.16 only, I believe.

-boris



> If not, I'll 
> submit the request after it is in Linus's tree.
>
> -Jason