From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C03A7C433EF for ; Thu, 28 Oct 2021 17:43:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 951A060F38 for ; Thu, 28 Oct 2021 17:43:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230174AbhJ1RqR (ORCPT ); Thu, 28 Oct 2021 13:46:17 -0400 Received: from mail.skyhub.de ([5.9.137.197]:36016 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229610AbhJ1RqR (ORCPT ); Thu, 28 Oct 2021 13:46:17 -0400 Received: from zn.tnic (p200300ec2f13a700349123b1f000d126.dip0.t-ipconnect.de [IPv6:2003:ec:2f13:a700:3491:23b1:f000:d126]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 11AA41EC067E; Thu, 28 Oct 2021 19:43:49 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1635443029; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=LV/QiZdF7ZKqnJvyt4f9O/KBxui21yF4wr9jzKFDXrY=; b=qIWNzriERo9OwiVILV1unRM52LETMnLqD3z4taQIYbRTcwlLNSDkB47m4F2nal4ODvWhVM w4+M1r126g/lvOGdl3krqz4WodnO5D2W6NkFwVoas+Cn1RunTatMwxHEAvo9Ipf6dTk/9m zn3qhAel7oTvjr4iS1fpAWUK6sTL+04= Date: Thu, 28 Oct 2021 19:43:45 +0200 From: Borislav Petkov To: Peter Zijlstra Cc: x86@kernel.org, jpoimboe@redhat.com, andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org, alexei.starovoitov@gmail.com, ndesaulniers@google.com, bpf@vger.kernel.org Subject: Re: [PATCH v3 00/16] x86: Rewrite the retpoline rewrite logic Message-ID: References: <20211026120132.613201817@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211026120132.613201817@infradead.org> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Oct 26, 2021 at 02:01:32PM +0200, Peter Zijlstra wrote: > Hi, > > These patches rewrite the way retpolines are rewritten. Currently objtool emits > alternative entries for most retpoline calls. However trying to extend that led > to trouble (ELF files are horrid). > > Therefore completely overhaul this and have objtool emit a .retpoline_sites > section that lists all compiler generated retpoline thunk calls. Then the > kernel can do with them as it pleases. > > Notably it will: > > - rewrite them to indirect instructions for !RETPOLINE > - rewrite them to lfence; indirect; for RETPOLINE_AMD, > where size allows (boo clang!) > > Specifically, the !RETPOLINE case can now also deal with the clang-special > conditional-indirect-tail-call: > > Jcc __x86_indirect_thunk_\reg. > > Finally, also update the x86 BPF jit to catch up to recent times and do these > same things. > > All this should help improve performance by removing an indirection. > > Patches can (soon) be found here: > > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git objtool/core > > Changes since v2: > > - rewrite the __x86_indirect_thunk_array[] stuff again > - rewrite the retpoline,amd rewrite logic, it now also supports > rewriting the Jcc case, if the original instruction is long enough, but > more importantly, it's simpler code. > - bpf label simplification patch > - random assorted cleanups > - actually managed to get bpf selftests working > > --- > arch/um/kernel/um_arch.c | 4 + > arch/x86/include/asm/GEN-for-each-reg.h | 14 ++- > arch/x86/include/asm/alternative.h | 1 + > arch/x86/include/asm/asm-prototypes.h | 18 --- > arch/x86/include/asm/nospec-branch.h | 72 ++--------- > arch/x86/kernel/alternative.c | 189 ++++++++++++++++++++++++++++- > arch/x86/kernel/cpu/bugs.c | 7 -- > arch/x86/kernel/module.c | 9 +- > arch/x86/kernel/vmlinux.lds.S | 14 +++ > arch/x86/lib/retpoline.S | 56 ++------- > arch/x86/net/bpf_jit_comp.c | 160 +++++++++--------------- > arch/x86/net/bpf_jit_comp32.c | 22 +++- > tools/objtool/arch/x86/decode.c | 120 ------------------ > tools/objtool/check.c | 208 ++++++++++++++++++++++---------- > tools/objtool/elf.c | 84 ------------- > tools/objtool/include/objtool/check.h | 1 - > tools/objtool/include/objtool/elf.h | 6 +- > tools/objtool/special.c | 8 -- > 18 files changed, 472 insertions(+), 521 deletions(-) Ok, this all looks real nice, thx! Reviewed-by: Borislav Petkov -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette