From patchwork Wed Oct 27 08:52:55 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 12586739 X-Patchwork-Delegate: bpf@iogearbox.net 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 E857CC433EF for ; Wed, 27 Oct 2021 09:00:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D238C60FC0 for ; Wed, 27 Oct 2021 09:00:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241161AbhJ0JCc (ORCPT ); Wed, 27 Oct 2021 05:02:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241152AbhJ0JC2 (ORCPT ); Wed, 27 Oct 2021 05:02:28 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69FE0C061348 for ; Wed, 27 Oct 2021 02:00:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:To:From:Date:Message-ID:Sender:Reply-To:Cc:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=2v3uIvVPHvF6X4QD+1Tv1yg25b3qVdoNykrE8xV5weA=; b=KMrBiUbItLUw+L4C6EWrePOC4a /Hlb7G9HMVZeP63BabBz9AAtSuPwI2TOKeCGc3Ib4y/9tfpCjcO0nfigvgmIuAe8pBFsQGEraFECa p0+YsvsQFEr9ZLCtTxwLcKbeSeX/fC7yXwoVDBdaEbAfhhG26Laz9JalRXrvKKh6q5lqRI6Z1ju49 oAQ0+bGoAmRNxBmNqu8QcWhE+129FgWrGSisy4zPUo5MzcKshkwhSepzP8yKSrHDHY362znzAVL/t QZH/3h2pgAhTdW1L+0TpYDhkwhzGNjqGSu37VGsr4HVvxf3Pi5Uqnj+QbOYqHQR2wtfvcNc/3sFwH m3noRTPw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mfelQ-00HWTL-5M for bpf@vger.kernel.org; Wed, 27 Oct 2021 08:58:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id AC1EF301994 for ; Wed, 27 Oct 2021 10:58:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 9E5D8236E43DA; Wed, 27 Oct 2021 10:58:20 +0200 (CEST) Message-ID: <20211027085520.838533099@infradead.org> User-Agent: quilt/0.66 Date: Wed, 27 Oct 2021 10:52:55 +0200 From: Peter Zijlstra To: bpf@vger.kernel.org Subject: [PATCH bpf-next 12/17] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg References: <20211027085243.008677168@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Handle the rare cases where the compiler (clang) does an indirect conditional tail-call using: Jcc __x86_indirect_thunk_\reg For the !RETPOLINE case this can be rewritten to fit the original (6 byte) instruction like: Jncc.d8 1f JMP *%\reg NOP 1: Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/alternative.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -393,7 +393,8 @@ static int emit_indirect(int op, int reg static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) { retpoline_thunk_t *target; - int reg, i = 0; + int reg, ret, i = 0; + u8 op, cc; target = addr + insn->length + insn->immediate.value; reg = target - __x86_indirect_thunk_array; @@ -407,9 +408,34 @@ static int patch_retpoline(void *addr, s if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) return -1; - i = emit_indirect(insn->opcode.bytes[0], reg, bytes); - if (i < 0) - return i; + op = insn->opcode.bytes[0]; + + /* + * Convert: + * + * Jcc.d32 __x86_indirect_thunk_\reg + * + * into: + * + * Jncc.d8 1f + * JMP *%\reg + * NOP + * 1: + */ + if (op == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80) { + cc = insn->opcode.bytes[1] & 0xf; + cc ^= 1; /* invert condition */ + + bytes[i++] = 0x70 + cc; /* Jcc.d8 */ + bytes[i++] = insn->length - 2; + + op = JMP32_INSN_OPCODE; + } + + ret = emit_indirect(op, reg, bytes + i); + if (ret < 0) + return ret; + i += ret; for (; i < insn->length;) bytes[i++] = BYTES_NOP1; @@ -443,6 +469,10 @@ void __init_or_module noinline apply_ret case JMP32_INSN_OPCODE: break; + case 0x0f: /* escape */ + if (op2 >= 0x80 && op2 <= 0x8f) + break; + fallthrough; default: WARN_ON_ONCE(1); continue;