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client-ip=162.221.158.21; receiver=esa4.hc3370-68.iphmx.com; envelope-from="Andrew.Cooper3@citrix.com"; x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible Authentication-Results: esa4.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=andrew.cooper3@citrix.com; spf=Pass smtp.mailfrom=Andrew.Cooper3@citrix.com; spf=None smtp.helo=postmaster@mail.citrix.com; dmarc=pass (p=none dis=none) d=citrix.com IronPort-SDR: 000k+0R0nErGb8NbHz0FFJQ5jkiWORs981K8+ywmfEg2ECNkXaLzuKfeGqxZ6w8+MgNgToU0GM XzKUNr/OQS1v5utgFig7Vul30YuI8GdX7gGd9sC0wlZIPjzUmVZ1ZKWShwfj85Vab8f0IapLFn RoNmqaG+VG0HeqkzeZ3iO88Q3y80ZDMMLMNWDEjRRgX3t6NOXZOpOhOPv51NlCIwlHz+e+k2fh ic7Y5menFrEfwlJyFxMVS2t02hyHNmhGMZBW+IpJ+rMGZ/2J2g2ZoBFiC51HVumYpkcerfOWGc dC8= X-SBRS: 2.7 X-MesageID: 17932759 X-Ironport-Server: esa4.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.73,380,1583211600"; d="scan'208";a="17932759" Subject: Re: [PATCH 07/16] x86/shstk: Re-layout the stack block for shadow stacks To: Jan Beulich References: <20200501225838.9866-1-andrew.cooper3@citrix.com> <20200501225838.9866-8-andrew.cooper3@citrix.com> <8b6e03ee-545d-eada-457e-79c183a72d6d@suse.com> From: Andrew Cooper Message-ID: <51eca0a6-48ff-9169-2c41-c1cadace1d02@citrix.com> Date: Mon, 11 May 2020 18:48:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <8b6e03ee-545d-eada-457e-79c183a72d6d@suse.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS01.citrite.net (10.69.22.112) To AMSPEX02CL02.citrite.net (10.69.22.126) X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 04/05/2020 15:24, Jan Beulich wrote: > On 02.05.2020 00:58, Andrew Cooper wrote: >> --- a/xen/arch/x86/cpu/common.c >> +++ b/xen/arch/x86/cpu/common.c >> @@ -732,14 +732,14 @@ void load_system_tables(void) >> .rsp2 = 0x8600111111111111ul, >> >> /* >> - * MCE, NMI and Double Fault handlers get their own stacks. >> + * #DB, NMI, DF and #MCE handlers get their own stacks. > Then also #DF and #MC? Ok. > >> --- a/xen/arch/x86/mm.c >> +++ b/xen/arch/x86/mm.c >> @@ -6002,25 +6002,18 @@ void memguard_unguard_range(void *p, unsigned long l) >> >> void memguard_guard_stack(void *p) >> { >> - /* IST_MAX IST pages + at least 1 guard page + primary stack. */ >> - BUILD_BUG_ON((IST_MAX + 1) * PAGE_SIZE + PRIMARY_STACK_SIZE > STACK_SIZE); >> + map_pages_to_xen((unsigned long)p, virt_to_mfn(p), 1, _PAGE_NONE); >> >> - memguard_guard_range(p + IST_MAX * PAGE_SIZE, >> - STACK_SIZE - PRIMARY_STACK_SIZE - IST_MAX * PAGE_SIZE); >> + p += 5 * PAGE_SIZE; > The literal 5 here and ... > >> + map_pages_to_xen((unsigned long)p, virt_to_mfn(p), 1, _PAGE_NONE); >> } >> >> void memguard_unguard_stack(void *p) >> { >> - memguard_unguard_range(p + IST_MAX * PAGE_SIZE, >> - STACK_SIZE - PRIMARY_STACK_SIZE - IST_MAX * PAGE_SIZE); >> -} >> - >> -bool memguard_is_stack_guard_page(unsigned long addr) >> -{ >> - addr &= STACK_SIZE - 1; >> + map_pages_to_xen((unsigned long)p, virt_to_mfn(p), 1, PAGE_HYPERVISOR_RW); >> >> - return addr >= IST_MAX * PAGE_SIZE && >> - addr < STACK_SIZE - PRIMARY_STACK_SIZE; >> + p += 5 * PAGE_SIZE; > ... here could do with macro-izing: IST_MAX + 1 would already be > a little better, I guess. The problem is that "IST_MAX + 1" is now less meaningful than a literal 5, because at least 5 obviously matches up with the comment describing which page does what. ~Andrew > > Preferably with adjustments along these lines > Reviewed-by: Jan Beulich > > Jan