From patchwork Tue Oct 26 12:01:43 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 12584775 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 BFAD5C4332F for ; Tue, 26 Oct 2021 12:08:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A64C8610CB for ; Tue, 26 Oct 2021 12:08:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235632AbhJZMK3 (ORCPT ); Tue, 26 Oct 2021 08:10:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233642AbhJZMKZ (ORCPT ); Tue, 26 Oct 2021 08:10:25 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1C0CC061243; Tue, 26 Oct 2021 05:08:01 -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=2v3uIvVPHvF6X4QD+1Tv1yg25b3qVdoNykrE8xV5weA=; b=A8SulDwX1eGTB0V4PPlfEa+L+o 2bOCW1LNZ59qMSYeBXr93awOfFrmqPjdPft1u9vNM9yE3HOD2EtLJCla0V3M0p27SzU5DynpNkKy4 Lf3tK9yEF7webT7cYmZUlAob37ZTTYuwGNxVszuKj33lrMqgKIJUjdC98uQPNlxVBNNKTZiCegRLN qHAWQ6ehL6/uYtG47UhTOtPnSa/9eSG0RFwtLUCCVLo5jHO8TitggwiMqKAEvpwYYjbpaeCigRUUq RGFTFb7iU/TA+WhqkXB0dywb5NQCmfCCHDHpgelNDr8YmWXXCLL1amQJvQ/Fpu3aE9OQ67uErEDKG mas7+gfw==; 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 1mfLCe-00GprJ-7d; Tue, 26 Oct 2021 12:05:25 +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 43C8E30198B; Tue, 26 Oct 2021 14:05:14 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 2788925E57E60; Tue, 26 Oct 2021 14:05:14 +0200 (CEST) Message-ID: <20211026120310.296470217@infradead.org> User-Agent: quilt/0.66 Date: Tue, 26 Oct 2021 14:01:43 +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, bpf@vger.kernel.org Subject: [PATCH v3 11/16] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg References: <20211026120132.613201817@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@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) { 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;