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SubjectRe: [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

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