From nobody Wed Dec 17 23:28:38 2025 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 0528CC0015E for ; Tue, 15 Aug 2023 23:09:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240536AbjHOXJI (ORCPT ); Tue, 15 Aug 2023 19:09:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240526AbjHOXIl (ORCPT ); Tue, 15 Aug 2023 19:08:41 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 62E65BC for ; Tue, 15 Aug 2023 16:08:40 -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:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=jbwfzUfYwAhMlh7v4ac7NWW4BAx8Lm8Q9u70PaxXfWs=; b=AglFnBZgkijyTGw5EcYzT+X6Iq rdUFjovtFNW7j/tW4MSZShJvIQzXzYZwKNbIwQMqTIacCdWi5Qk6SBqQkjmnDavG5PEJLe6y7NRb8 LZkgJ/JedXTBmt2nQHjMgU9UMdWq1StN34/iBjXT/fPFZZ3KjbNrZVjtigTvvNVUcpziBqmxJ8ybi YjLm8MzMof1IUmPkORhM6P4s9TO5o4f++2k+RVmNeHDUOKkjIB6eJ+5auDj1ztpKEbIuSJ4/ZqAdI 4M/mQS3QvgrW7iWb/99qAot/u/APtklZ8ZAMXCaUuvwcpiLGqb1gyILpjW6qiVPhZrrUPy335UU+W XGe7ABvQ==; 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 1qW390-00B50N-Sc; Tue, 15 Aug 2023 23:08:11 +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 24599300222; Wed, 16 Aug 2023 01:08:10 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 025B720307331; Wed, 16 Aug 2023 01:08:09 +0200 (CEST) Date: Wed, 16 Aug 2023 01:08:09 +0200 From: Peter Zijlstra To: jpoimboe@kernel.org, x86@kernel.org Cc: baron@akamai.com, rostedt@goodmis.org, ardb@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, christian@bricart.de, song@kernel.org, mcgrof@kernel.org Subject: [PATCH] x86/static_call: Fix __static_call_fixup() Message-ID: <20230815230809.GA973560@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Christian reported spurious module crashes after some of Song's module memory layout patches. Turns out that if the very last instruction on the very last page of the module is a 'JMP __x86_return_thunk' then __static_call_fixup() will trip a fault and dies. And while the module rework made this slightly more likely to happen, it's always been possible. Fixes: ee88d363d156 ("x86,static_call: Use alternative RET encoding") Reported-by: Christian Bricart Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/static_call.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index b70670a98597..2e67512d7104 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -186,6 +186,16 @@ EXPORT_SYMBOL_GPL(arch_static_call_transform); */ bool __static_call_fixup(void *tramp, u8 op, void *dest) { + /* + * Not all .return_sites are a static_call trampoline (most are not). + * Check if the next 3 bytes are still kernel text, if not, then this + * definitely is not a trampoline and we need not worry further. + * + * This avoids the memcmp() below tripping over pagefaults etc.. + */ + if (!kernel_text_address(tramp+7)) + return false; + if (memcmp(tramp+5, tramp_ud, 3)) { /* Not a trampoline site, not our problem. */ return false;