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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A197EB64D8 for ; Thu, 22 Jun 2023 14:51:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231977AbjFVOvH (ORCPT ); Thu, 22 Jun 2023 10:51:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231913AbjFVOuj (ORCPT ); Thu, 22 Jun 2023 10:50:39 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2462FE7E for ; Thu, 22 Jun 2023 07:50:38 -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=r2emQb1KTou2w3E9LTe7OUggXTTKEQJMuYJi6cUiILo=; b=ojMRDX4ZBEo3NUsxlNBhbZLvLt fkA47p2jhqe8lzrjurlZD2De4pLm2TykWc791yVF/zL0xFJOdfWxq++Veod7TQ+XhUdasBxrjX8nN OPAOuz0MCUzYEi5uA94oEvnGBs/JxIEIewilpDBPNdDupmEPS2IQkauXWZ1vv9BQ0B4FqjdrHr9/k uz//mQ/fof1UKUzFvRn3jAOYUN6rNV20xLBwELPIXwHorcoG27Mi7SDZOq2BCt3HWvJBLHzwNlkWM jBEnghKq3fIWQ5vkBpYn7CMxzJOb13s5sOeop9IS55tSD/6RdDNLVPyBCkK7oQ7E5V7V/TqIP49tf wSh7KL6A==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qCLdh-00FgfE-V5; Thu, 22 Jun 2023 14:50:26 +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 (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7716F300790; Thu, 22 Jun 2023 16:50:24 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 29E62209FB79B; Thu, 22 Jun 2023 16:50:24 +0200 (CEST) Message-ID: <20230622144321.696656240@infradead.org> User-Agent: quilt/0.66 Date: Thu, 22 Jun 2023 16:42:24 +0200 From: Peter Zijlstra To: x86@kernel.org, alyssa.milburn@linux.intel.com Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, samitolvanen@google.com, keescook@chromium.org, jpoimboe@kernel.org, joao@overdrivepizza.com, brgerst@gmail.com, "Milburn, Alyssa" Subject: [PATCH v2 6/6] x86/fineibt: Poison ENDBR at +0 References: <20230622144218.860926475@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 Alyssa noticed that when building the kernel with CFI_CLANG+IBT and booting on IBT enabled hardware to obtain FineIBT, the indirect functions look like: __cfi_foo: endbr64 subl $hash, %r10d jz 1f ud2 nop 1: foo: endbr64 This is because the compiler generates code for kCFI+IBT. In that case the caller does the hash check and will jump to +0, so there must be an ENDBR there. The compiler doesn't know about FineIBT at all; also it is possible to actually use kCFI+IBT when booting with 'cfi=kcfi' on IBT enabled hardware. Having this second ENDBR however makes it possible to elide the CFI check. Therefore, we should poison this second ENDBR when switching to FineIBT mode. Fixes: 931ab63664f0 ("x86/ibt: Implement FineIBT") Reported-by: "Milburn, Alyssa" Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Sami Tolvanen Acked-by: Kees Cook Link: https://lore.kernel.org/r/20230615193722.194131053@infradead.org --- arch/x86/kernel/alternative.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1063,6 +1063,17 @@ static int cfi_rewrite_preamble(s32 *sta return 0; } +static void cfi_rewrite_endbr(s32 *start, s32 *end) +{ + s32 *s; + + for (s = start; s < end; s++) { + void *addr = (void *)s + *s; + + poison_endbr(addr+16, false); + } +} + /* .retpoline_sites */ static int cfi_rand_callers(s32 *start, s32 *end) { @@ -1157,14 +1168,19 @@ static void __apply_fineibt(s32 *start_r return; case CFI_FINEIBT: + /* place the FineIBT preamble at func()-16 */ ret = cfi_rewrite_preamble(start_cfi, end_cfi); if (ret) goto err; + /* rewrite the callers to target func()-16 */ ret = cfi_rewrite_callers(start_retpoline, end_retpoline); if (ret) goto err; + /* now that nobody targets func()+0, remove ENDBR there */ + cfi_rewrite_endbr(start_cfi, end_cfi); + if (builtin) pr_info("Using FineIBT CFI\n"); return;