From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C47281171A for ; Mon, 21 Aug 2023 20:01:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8CF6C433C8; Mon, 21 Aug 2023 20:01:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1692648066; bh=dbRHxPMkQ9nrNWUKoWZNWzUzsxBX/FS2dqF9mwM0wSM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Zgo36UyQP8jc/RRIV6GOYcjk0vpIRt6HKZwFPFZ+6gDHCoY3qOu9Tvu2Hr7YXCX9E Bu1qF6yPhcuv502vwvkWp2dfTdkxpJ8KfZaD3Pi13VAUv/riHw2xTg/bzLUoHvZe3n 4HWdMgDOWiVWcL0wYUzm1qAdbbCFKF+cF3fD4ZlQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Masahiro Yamada , Nick Desaulniers , Sasha Levin Subject: [PATCH 6.4 043/234] Revert "[PATCH] uml: export symbols added by GCC hardened" Date: Mon, 21 Aug 2023 21:40:06 +0200 Message-ID: <20230821194130.636870207@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230821194128.754601642@linuxfoundation.org> References: <20230821194128.754601642@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Masahiro Yamada [ Upstream commit 8635e8df477bc77837886da206f4915576f88fec ] This reverts commit cead61a6717a9873426b08d73a34a325e3546f5d. It exported __stack_smash_handler and __guard, while they may not be defined by anyone. The code *declares* __stack_smash_handler and __guard. It does not create weak symbols. If no external library is linked, they are left undefined, but yet exported. If a loadable module tries to access non-existing symbols, bad things (a page fault, NULL pointer dereference, etc.) will happen. So, the current code is wrong and dangerous. If the code were written as follows, it would *define* them as weak symbols so modules would be able to get access to them. void (*__stack_smash_handler)(void *) __attribute__((weak)); EXPORT_SYMBOL(__stack_smash_handler); long __guard __attribute__((weak)); EXPORT_SYMBOL(__guard); In fact, modpost forbids exporting undefined symbols. It shows an error message if it detects such a mistake. ERROR: modpost: "..." [...] was exported without definition Unfortunately, it is checked only when the code is built as modular. The problem described above has been unnoticed for a long time because arch/um/os-Linux/user_syms.c is always built-in. With a planned change in Kbuild, exporting undefined symbols will always result in a build error instead of a run-time error. It is a good thing, but we need to fix the breakage in advance. One fix is to define weak symbols as shown above. An alternative is to export them conditionally as follows: #ifdef CONFIG_STACKPROTECTOR extern void __stack_smash_handler(void *); EXPORT_SYMBOL(__stack_smash_handler); external long __guard; EXPORT_SYMBOL(__guard); #endif This is what other architectures do; EXPORT_SYMBOL(__stack_chk_guard) is guarded by #ifdef CONFIG_STACKPROTECTOR. However, adding the #ifdef guard is not sensible because UML cannot enable the stack-protector in the first place! (Please note UML does not select HAVE_STACKPROTECTOR in Kconfig.) So, the code is already broken (and unused) in multiple ways. Just remove. Signed-off-by: Masahiro Yamada Reviewed-by: Nick Desaulniers Signed-off-by: Sasha Levin --- arch/um/os-Linux/user_syms.c | 7 ------- 1 file changed, 7 deletions(-) diff --git a/arch/um/os-Linux/user_syms.c b/arch/um/os-Linux/user_syms.c index 9b62a9d352b3a..a310ae27b479a 100644 --- a/arch/um/os-Linux/user_syms.c +++ b/arch/um/os-Linux/user_syms.c @@ -37,13 +37,6 @@ EXPORT_SYMBOL(vsyscall_ehdr); EXPORT_SYMBOL(vsyscall_end); #endif -/* Export symbols used by GCC for the stack protector. */ -extern void __stack_smash_handler(void *) __attribute__((weak)); -EXPORT_SYMBOL(__stack_smash_handler); - -extern long __guard __attribute__((weak)); -EXPORT_SYMBOL(__guard); - #ifdef _FORTIFY_SOURCE extern int __sprintf_chk(char *str, int flag, size_t len, const char *format); EXPORT_SYMBOL(__sprintf_chk); -- 2.40.1