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

On Sat, Mar 31, 2018 at 2:10 PM, Boris Ostrovsky boris.ostrovsky@oracle.com wrote:

On 03/31/2018 01:38 PM, Jason Andryuk wrote:

...

On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky <boris.ostrovsky@oracle.com mailto:boris.ostrovsky@oracle.com> 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:    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 <jandryuk@gmail.com
<mailto:jandryuk@gmail.com>>
 >


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.

I'm using this patch on 4.14, so there as well.

-Jason