linux-kernel - Re: [Xen-devel] [PATCH v2 1/2] xen/PVH: Set up GS segment for stack canary

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Message-ID: <b0c80258-008a-9b4e-38c9-a5451b59c44e@oracle.com>
Date:   Mon, 14 May 2018 14:27:39 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     xen-devel <xen-devel@...ts.xenproject.org>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH v2 1/2] xen/PVH: Set up GS segment for stack
 canary

On 05/14/2018 08:50 AM, Jan Beulich wrote:
>>>> On 09.05.18 at 22:33, <boris.ostrovsky@...cle.com> wrote:
>> @@ -64,6 +67,17 @@ ENTRY(pvh_start_xen)
>>  	mov %eax,%es
>>  	mov %eax,%ss
>>  
>> +	/* Set base address in stack canary descriptor. */
>> +	movl _pa(gdt_start),%eax
>> +	movl $_pa(canary),%ecx
>> +	movw %cx, (PVH_GDT_ENTRY_CANARY * 8) + 0(%eax)
>> +	shrl $16, %ecx
>> +	movb %cl, (PVH_GDT_ENTRY_CANARY * 8) + 2(%eax)
>> +	movb %ch, (PVH_GDT_ENTRY_CANARY * 8) + 5(%eax)
> Is this meaningful / correct for the 64-bit case? I'd rather expect you to
> write the GS base address MSR there.

Yes, I should use the MSR for 64-bit mode and existing code for 32-bit mode.

-boris