From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: xen/link: Move .data.rel.ro sections into .rodata for final link Date: Wed, 02 Aug 2017 12:43:54 +0100 Message-ID: <1501674234.4771.398.camel@infradead.org> References: <1500564043.4400.15.camel@infradead.org> <597D79BD0200007800102F92@prv-mh.provo.novell.com> <1501498940.4771.251.camel@infradead.org> <597F2D860200007800103049@prv-mh.provo.novell.com> <1501516597.4771.328.camel@infradead.org> <598198C30200007800103235@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============2672165285867382752==" Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcs6V-0000SI-SH for xen-devel@lists.xenproject.org; Wed, 02 Aug 2017 11:46:20 +0000 In-Reply-To: <598198C30200007800103235@prv-mh.provo.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" To: Jan Beulich Cc: xen-devel@lists.xenproject.org, jiewen.yao@intel.com, jeff.fan@intel.com, mark.doran@intel.com List-Id: xen-devel@lists.xenproject.org --===============2672165285867382752== Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-Z7FMbiKt+rBMRDNFFnng" --=-Z7FMbiKt+rBMRDNFFnng Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2017-08-02 at 03:17 -0600, Jan Beulich wrote: >=20 > >... but then again, if the whole function is really doing nothing at > >all when invoked with delta=3D=3D0 then perhaps it would just be easier = to > >remove the first pass altogether. I feel sure I'm missing something, >=20 > The reason is even visible in context above: We can't call blexit() after > having called ExitBootServices(). Hence we need a "dry run" done early, > to be certain we won't encounter unhandlable relocations later on. Ah, thanks. I'd glossed over that as a "can never happen" condition. And the 'default:' case really is that =E2=80=94 the build system is broken= if we ever see that. But the DIR64 / in_page_tables() one is less provably impossible. > >Either way, this is still broken before my patch though, right? >=20 > As long as there are .rodata entries needing relocation (which I > understand you've found example of), yes. And more to the point, .init.text entries needing relocation (since UEFI isn't marking read-only *data* sections read-only yet for some reason; only R+X sections). But still that basically means that new versions of UEFI are going to stop booting all existing EFI Xen images, doesn't it? Perhaps we should look for a mitigation on the UEFI side. Jeff, Jiewen, has this actually been shipped in an EDK2 release yet? I confess I haven't actually built a current OVMF and *tested* the hypothesis that it breaks; it just seems "obvious" :) Adding Mark. Background: we think https://github.com/tianocore/edk2/commit/d0e92aad46=C2=A0will break existin= g Xen EFI binaries because they write to a read-only code section (.init.te) before calling ExitBootServices(). --=-Z7FMbiKt+rBMRDNFFnng Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDzUw ggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQswCQYDVQQG EwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVybmFsIFRU UCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MB4XDTE0MTIyMjAw MDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1h bmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMUEw PwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBF bWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAImxDdp6UxlOcFIdvFamBia3 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