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Subject: Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is
 established
To:     Jason Andryuk <jandryuk@gmail.com>
Cc:     Juergen Gross <jgross@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
References: <20180319165804.10636-1-jandryuk@gmail.com>
 <c3075b0c-a60b-0809-e34b-223701a53b84@oracle.com>
 <CAKf6xps0HJecKM0gYSK+3BGhKknYp9Ydxr3S0oWBThtXeytegw@mail.gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <ee25829c-e8de-1171-e54e-3b34206acc9e@oracle.com>
Date:   Sat, 31 Mar 2018 14:10:49 -0400
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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.

-boris


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