Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933028AbeAKKAV (ORCPT + 1 other); Thu, 11 Jan 2018 05:00:21 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:44547 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932362AbeAKKAU (ORCPT ); Thu, 11 Jan 2018 05:00:20 -0500 X-Amazon-filename: smime.p7s X-IronPort-AV: E=Sophos;i="5.46,343,1511827200"; d="p7s'?scan'208";a="585604630" Message-ID: <1515664721.22302.309.camel@amazon.co.uk> Subject: Re: [PATCH] x86/retpoline: Fill return stack buffer on vmexit To: Borislav Petkov , Peter Zijlstra CC: "Thomas.Lendacky@amd.com" , "linux-kernel@vger.kernel.org" , "tim.c.chen@linux.intel.com" , "Ghitulete, Razvan-alin" , "torvalds@linux-foundation.org" , "tglx@linutronix.de" , "ak@linux.intel.com" , "x86@kernel.org" , "riel@redhat.com" , "keescook@google.com" , "gnomes@lxorguk.ukuu.org.uk" , "pjt@google.com" , "dave.hansen@intel.com" , "luto@amacapital.net" , "jikos@kernel.org" , "gregkh@linux-foundation.org" In-Reply-To: <20180111094759.aohvm5tqztza72es@pd.tnic> References: <1515624682-3556-1-git-send-email-dwmw@amazon.co.uk> <5371f9a0-f221-af1f-641f-05e4d0991847@linux.intel.com> <1515629074.22302.282.camel@amazon.co.uk> <20180111084238.GT6176@hirez.programming.kicks-ass.net> <1F5F831F-0C4B-4DA9-8A48-D0D1C1ADC0D7@alien8.de> <1515661628.22302.294.camel@amazon.co.uk> <20180111093231.GX6176@hirez.programming.kicks-ass.net> <20180111094759.aohvm5tqztza72es@pd.tnic> Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAG1BMVEUHBwcUFBQpKSlGRkZhYWF9fX2Xl5eysrLMzMxFF+rXAAACaElEQVQ4y21UQXbbIBQE9wJALmAg6ToWON22FrhZthHgbvssUPathC7QWMful2JHSmtWwGg+zPxBCE0DU4QoJQgRgsg4w2gJjBNE8PjFBZgnQMBs+uZ1NQNQjZO3BV4AGDFC0f+l4DBG0VUAM4yv7SO8IgRdHXQ+A78HKL5OAeCfNQV5cHX8DsBUyIJKtYbt98BKaGNCKjfgFVkqYVLbkHKsRsbSCSa0T6npIqLrpRBgQKHUpQmgs9eEKaiUcooE8WWfCGVnBiUcn1uF2XhbfmN9apKnmMP2K4kizKkQWxuaVNOpU2cACIyxO1Po8ETHcXEDMVnozcejkAYA9iaD4pU0ZvNQ8VurNnTuFAYVtuIPUZW25PjDIjQAlGyffIiRQxoWAZBmJ0LTdW2Nyc0iP3DqRhxizvGJkBWZmyFVyZkddWzmBoIBVMpCCJ1CFzl98xav4VJKSSD45KbUT75ixikTphDSRh8+Uz7JLgUTAgAFwzqzjxc/nDY7WUApqY0OMdTwCKZSXplSKkgIRCHElCp8ZnhnKqXuwcNbk1L0VXE+I9alUXoHlLHl3mv7/dWQlJwtjREC7mu9L/U2jQyMUuO2EDS4q9Kl2ddm232bxIE5pjJuVwiljNn/Cfv25/T0cu5cZbwHGVq7h/zp0B4n3S99V/utD+Uo8BiGx9xCsOAV5z7/tjo4Z4z1Lvb90KZ7eFOoOeXOukqF2seo234YYuaQPpRP+cVZU5adT1Edun5Iz3z8fTz3+eSDh0Ip1c7zx1MaijGzTd/3MbRuBHz8cvcVgCMBRpOHvgu59WDhoat+nIZm+LWm9C/aaaGq5DCP9QAAAABJRU5ErkJggg== Organization: Amazon Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-r4h8kyxEsDfuuJx8kFgX" Date: Thu, 11 Jan 2018 09:58:41 +0000 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 MIME-Version: 1.0 From: "Woodhouse, David" X-Evolution-Source: 1481217574.17989.4@uc8d3ff76b9bc5848a9cc Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-r4h8kyxEsDfuuJx8kFgX Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2018-01-11 at 10:47 +0100, Borislav Petkov wrote: > On Thu, Jan 11, 2018 at 10:32:31AM +0100, Peter Zijlstra wrote: > >=20 > > can't you do lovely things like: > >=20 > > volatile asm ("call __fill_rsb_thunk_%1" : : "r" (dummy)) > >=20 > > which would still let gcc select the register ? I've had to do that for the __x86_indirect_thunk_\reg thunks and provide all variants thereof, and export them to modules. I'd much rather have this one inline. If I couldn't do that (which I can, and have), then my next choice would probably have been to just hard-code it to use %eax/%r12 and emit a simple call to that from the call sites. > Calling a function from asm is nasty because you need to pay attention > to clobbered registers as gcc doesn't see the function. > > What one can do, I *think*, is do a non-inlined wrapping function and do > all the alternative_call() fun inside. There you can do all the fun and > have callee-clobbered regs which you can use. That's OK; it's not really a C function and it only clobbers the *one* register which is easy enough to tell __asm__() about. --=-r4h8kyxEsDfuuJx8kFgX Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEE4w ggUuMIIEFqADAgECAhEApEtL31g6H7ROXdOiQnA9RjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTcxMjIxMDAwMDAwWhcNMTgxMjIxMjM1 OTU5WjAiMSAwHgYJKoZIhvcNAQkBFhFkd213QGFtYXpvbi5jby51azCCASIwDQYJKoZIhvcNAQEB BQADggEPADCCAQoCggEBAKdGKgXuwKMg2r+i/4BZZC0ddRxNq3xIKTakie/VCSzoO7P17A36ZzUc VMEYPfqDt/65xoc6Tdih+qkY2pNDppZ1DZ8mVrAX6O2O60ZhmXB60wMoDvXPZInvkMOW4drqnje/ 7/NOypn/XQAY+ln4KT+3tHG3TfryyJFMedqC/r29KJlCeeCxIzdtq2j5mN42tvPVv4+p+Kr77uui 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