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Wed, 2 May 2018 04:16:23 -0400 Received: from prv1-mh.provo.novell.com ([137.65.248.33]:42734 "EHLO prv1-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751220AbeEBIQW (ORCPT ); Wed, 2 May 2018 04:16:22 -0400 Message-Id: <5AE973CD02000078001C008E@prv1-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 18.0.0 Date: Wed, 02 May 2018 02:16:13 -0600 From: "Jan Beulich" To: "Boris Ostrovsky" Cc: "xen-devel" , "Juergen Gross" , , Subject: Re: [Xen-devel] [PATCH 3/4] xen/PVH: Set up GS segment for stack canary References: <20180430162339.17143-1-boris.ostrovsky@oracle.com> <20180430162339.17143-4-boris.ostrovsky@oracle.com> In-Reply-To: <20180430162339.17143-4-boris.ostrovsky@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: >>> On 30.04.18 at 18:23, wrote: > --- a/arch/x86/xen/xen-pvh.S > +++ b/arch/x86/xen/xen-pvh.S > @@ -54,6 +54,9 @@ > * charge of setting up it's own stack, GDT and IDT. > */ > > +#define PVH_GDT_ENTRY_CANARY 4 > +#define PVH_CANARY_SEL (PVH_GDT_ENTRY_CANARY * 8) I can only advise against doing it this way: There's no safeguard against someone changing asm/segment.h without changing this value (in fact this applies to all of the GDT selectors populated in this file). At the very least tie this to GDT_ENTRY_BOOT_TSS / __BOOT_TSS? > @@ -64,6 +67,9 @@ ENTRY(pvh_start_xen) > mov %eax,%es > mov %eax,%ss > > + mov $(PVH_CANARY_SEL),%eax > + mov %eax,%gs > + > /* Stash hvm_start_info. */ > mov $_pa(pvh_start_info), %edi > mov %ebx, %esi > @@ -150,6 +156,7 @@ gdt_start: > .quad 0x00cf9a000000ffff /* __BOOT_CS */ > #endif > .quad 0x00cf92000000ffff /* __BOOT_DS */ > + .quad 0x0040900000000018 /* PVH_CANARY_SEL */ Without any further code before loading the selector, this points at physical address 0. Don't you need to add in the base address of the per-CPU stack_canary? Jan