From nobody Sun Feb 8 22:58:19 2026 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 604E4EB64D9 for ; Thu, 15 Jun 2023 19:40:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231708AbjFOTkt (ORCPT ); Thu, 15 Jun 2023 15:40:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56828 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229694AbjFOTkn (ORCPT ); Thu, 15 Jun 2023 15:40:43 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6C66B2954 for ; Thu, 15 Jun 2023 12:40:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=BhX7pkXejcd+7jOdak4TeKh4gofIP/p6FvONT7yMD5Q=; b=Luncf/CUiCXEJyaixzGv2qhSHY FpBEa0sP9GHb+kSvFbCdnhUAl6ex0IbnWIihLc+vrU5Pw52VWmVi1dYIF5rgUcq/yBbQ5fnBT7C0I 3wroRla56ysNYuNVj7s6Ut8oxsy9oQhuc+xhs6KBlF8eUg6x7JKUC0cX1ZsK5DDlHv12G98EZjay1 cpv9C9FULKKGfXA4bevZK24nVZmoUtTU5Yo4WNZjwGTMnKbQQWdG5EqCJVOkajdE1H0p+FBVsmvSu YWvrH7dT6MjxhkaDEfbxUFnp+PZROLzB6Mfn5k5SkMpHhbmSh+wE8JWtqmXcPcMz3ZWUAJUMwTP2D mPoNrRow==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1q9spY-00BtUT-1s; Thu, 15 Jun 2023 19:40:29 +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) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 1018830031B; Thu, 15 Jun 2023 21:40:27 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id E847C245F1E4B; Thu, 15 Jun 2023 21:40:26 +0200 (CEST) Message-ID: <20230615193722.127844423@infradead.org> User-Agent: quilt/0.66 Date: Thu, 15 Jun 2023 21:35:47 +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, tim.c.chen@linux.intel.com Subject: [PATCH 1/2] x86/cfi: Fix ret_from_fork indirect calls References: <20230615193546.949657149@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The ret_from_fork stub does an indirect call to the kthread function, but only knows about Retpolines. Instead of making the asm more complicated, punt to C and let the compiler figure it out. Specifically, this makes it a proper kCFI indirect call when needed (in fact, it is nearly impossible to code a kCFI indirect call in asm). This was the only callsite that was still calling func()+0 on regular indirect functions. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Kees Cook Reviewed-by: Sami Tolvanen --- arch/x86/entry/entry_64.S | 6 ++++-- arch/x86/include/asm/switch_to.h | 2 ++ arch/x86/kernel/process_64.c | 5 +++++ 3 files changed, 11 insertions(+), 2 deletions(-) --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -304,8 +304,10 @@ SYM_CODE_START_NOALIGN(ret_from_fork) 1: /* kernel thread */ UNWIND_HINT_END_OF_STACK - movq %r12, %rdi - CALL_NOSPEC rbx + movq %rbx, %rdi + movq %r12, %rsi + call kthread_from_fork + /* * A kernel thread is allowed to return here after successfully * calling kernel_execve(). Exit to userspace to complete the execve() --- a/arch/x86/include/asm/switch_to.h +++ b/arch/x86/include/asm/switch_to.h @@ -74,6 +74,8 @@ static inline void update_task_stack(str #endif } =20 +extern void kthread_from_fork(int (*fn)(void *), void *); + static inline void kthread_frame_init(struct inactive_task_frame *frame, int (*fun)(void *), void *arg) { --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -544,6 +544,11 @@ void compat_start_thread(struct pt_regs } #endif =20 +__visible noinstr void kthread_from_fork(int (*fn)(void *), void *arg) +{ + fn(arg); +} + /* * switch_to(x,y) should switch tasks from x to y. *