From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757880AbeAHVu6 (ORCPT + 1 other); Mon, 8 Jan 2018 16:50:58 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:49996 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754028AbeAHVu4 (ORCPT ); Mon, 8 Jan 2018 16:50:56 -0500 Message-ID: <1515448250.4423.33.camel@infradead.org> Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support From: David Woodhouse To: Borislav Petkov Cc: Josh Poimboeuf , "tglx@linutronix.de" , "linux-kernel@vger.kernel.org" , "tim.c.chen@linux.intel.com" , "peterz@infradead.org" , "torvalds@linux-foundation.org" , "ak@linux.intel.com" , "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: <20180107140351.iukmbuf2xkqtvyoz@pd.tnic> References: <1515160619.29312.126.camel@amazon.co.uk> <1515170506.29312.149.camel@amazon.co.uk> <20180105164505.xpw5pefxsyu3z56e@pd.tnic> <20180105170806.mtylu2zagfxyj3ry@treble> <20180106003059.jhwx4ouc7xbt7yw6@pd.tnic> <1515227001.29312.205.camel@infradead.org> <20180106170243.ndkn3bfj5ezbijdd@pd.tnic> <1515318042.29312.311.camel@infradead.org> <20180107114645.yydecgoi4x53fyrd@pd.tnic> <1515327689.29312.319.camel@infradead.org> <20180107140351.iukmbuf2xkqtvyoz@pd.tnic> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-89EGGVa2xPCzesWQcfUP" Date: Mon, 08 Jan 2018 21:50:50 +0000 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-89EGGVa2xPCzesWQcfUP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2018-01-07 at 15:03 +0100, Borislav Petkov wrote: >=20 > My fear is if some funky compiler changes the sizes of the insns in > RETPOLINE_CALL/JMP and then the padding becomes wrong. But looking at the > labels, they're all close so you have a 2-byte jmp already and the >=20 > call=C2=A0=C2=A0=C2=A0 1112f >=20 > should be ok. The MOV is reg,(reg) which should not change size of 4... >=20 > But I'm remaining cautious here. Right. I forget the specifics, but I've *watched* LLVM break carefully hand-crafted asm code by emitting 4-byte variants when we expected 2- byte, etc. On the whole, I'm sufficiently unhappy with making such assumptions, that I think the cure is worse than the disease. We can live with that *one* out-of-line call to the thunk in the syscall case, and that was the *only* one that really needed the call to be at the end. Note that in the alternative case there, we don't even need to load it into a register at all. We could do our own alternatives specially for that case, and hand-tune the lengths only for them. But *with* a sanity check to break the build on mismatch. I don't think it's worth it at this point though. --=-89EGGVa2xPCzesWQcfUP Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEFQw ggUxMIIEGaADAgECAhBNRhEyk/HZ7naOeTHWrzuAMA0GCSqGSIb3DQEBCwUAMIGXMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTAeFw0xNzEyMjEwMDAwMDBaFw0xODEyMjEyMzU5 NTlaMCQxIjAgBgkqhkiG9w0BCQEWE2R3bXcyQGluZnJhZGVhZC5vcmcwggEiMA0GCSqGSIb3DQEB AQUAA4IBDwAwggEKAoIBAQDgzLNWa18DNpGUj/ZeH0Sgz53ESIbzdPw3OJeuNP6jZhxZojbyfxbM hETscxI/Hj6UZ4a7sHm5BkVjlsB1Af2Za/PXUt8MmLAcPMHkMPGunvkUibEvblDvpqMkQZlaZM+t 5PqFmWkbehLaEvbpNY7dmEAAeKh4klTzJzrr5AAzaCQ32cA2e3+DEIv5O5l9ViMIjy/JM+xMQrfX 3PZ0chY1PaVWjg59d4Uno+5LRDbgCnPkKJX4ysBGadibjBGQGJEZCjh94iiEebn2KsRLvtrJ72Ph 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