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

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Message-Id: <5AF9862C02000078001C27B5@prv1-mh.provo.novell.com>
Date:   Mon, 14 May 2018 06:50:52 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Boris Ostrovsky" <boris.ostrovsky@...cle.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 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.

Jan