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 62B35C4332F for ; Wed, 20 Oct 2021 11:04:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4DE69613B5 for ; Wed, 20 Oct 2021 11:04:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230268AbhJTLG3 (ORCPT ); Wed, 20 Oct 2021 07:06:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60352 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230174AbhJTLGU (ORCPT ); Wed, 20 Oct 2021 07:06:20 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06324C061765 for ; Wed, 20 Oct 2021 04:04:05 -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:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=xSMVP5j96yVHQwjbR9gNeckaGov+Y1BQGvjn8ahsflw=; b=S6ODRhq9HxfjnfJbB+gmA6h7Pl TjmBRm0KrK9dQdr6EVXM/MSLdaUVuNpg/n8yYWCZ+I0bMVq3DVJDOlkURtCQI//FGqZxVpTzsuGaF 6xpVmkS09g7SYcYOq8tSmv47IL2yO1IAmIe3CzcOeVnmoo94bB0bz7x8MeP//U6+1HYDxNuGNbalL oWoe87OI21I/9qiLwgyy6wb5CJ2MCoWg0/0gIdmFIqkCDcbRf2bBriH5MXAXy0xxxA3bZyE17Fua6 P/v7zC7jT2Z98jsgNUPQMYKxPOmxLBf9KEHTUSDbv+R8KVz3qO4poA6RRhkMXhT/HQSwt5GirUx5Y JXZ9IfAA==; 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 1md9L1-00CR12-9N; Wed, 20 Oct 2021 11:01:12 +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 2C2C73007C3; Wed, 20 Oct 2021 13:00:50 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 17070201BB3D0; Wed, 20 Oct 2021 13:00:50 +0200 (CEST) Message-ID: <20211020105843.102958676@infradead.org> User-Agent: quilt/0.66 Date: Wed, 20 Oct 2021 12:44:52 +0200 From: Peter Zijlstra To: x86@kernel.org, jpoimboe@redhat.com, andrew.cooper3@citrix.com Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, alexei.starovoitov@gmail.com, ndesaulniers@google.com Subject: [PATCH v2 10/14] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg References: <20211020104442.021802560@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) { void (*target)(void); - int reg, i = 0; + int reg, ret, i = 0; + u8 op, cc; target = addr + insn->length + insn->immediate.value; reg = (target - &__x86_indirect_thunk_rax) / @@ -408,9 +409,34 @@ 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; @@ -444,6 +470,10 @@ 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;