From patchwork Thu Jun 13 13:37:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zheng Yejian X-Patchwork-Id: 13696836 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) (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 0D3B4A94D; Thu, 13 Jun 2024 13:36:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.187 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718285806; cv=none; b=qWca11L3i0hc5iDQgJWA843OgQJtFTSG8l1OrJR/BXGYocIECiWA8nG1UykL4KU3mYKbrzWSv9HFuco/aaWhtGHVnMFfW+qtPynJvSZR+TW9yOhyj/4b82LuhyzzG1b785nDADBSnkYZzatzlU+ESKg/rQJMEdfWKp6XKGU6W3A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718285806; c=relaxed/simple; bh=crdyNwsLpflDPQo0G+t76e/7LQbMlKLEt8GfxsQJhn0=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=abE3eOByPbZnbAL6OmE3SeGCSusIanC0Vx/zsOMyihMCMc0J+Byj+tJFf2yjmQ5LBa3JnrmPDli/bHpKuLA0s/yguGn2xMDZpR4+j7BhNnglypCKA4WQEP/2PldfYgEn+UU0Phes7Gi2FdX5J1KRfkYXBUT+aseSZc1Sex5oSgw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.252]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4W0Ncw5QKGzwTS8; Thu, 13 Jun 2024 21:32:32 +0800 (CST) Received: from dggpeml500012.china.huawei.com (unknown [7.185.36.15]) by mail.maildlp.com (Postfix) with ESMTPS id 0E8DA180069; Thu, 13 Jun 2024 21:36:40 +0800 (CST) Received: from localhost.localdomain (10.67.175.61) by dggpeml500012.china.huawei.com (7.185.36.15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Thu, 13 Jun 2024 21:36:39 +0800 From: Zheng Yejian To: , , , , , , , , , , , , , , , , , , , , , , , CC: , , , , , , Subject: [PATCH 0/6] kallsyms: Emit symbol for holes in text and fix weak function issue Date: Thu, 13 Jun 2024 21:37:05 +0800 Message-ID: <20240613133711.2867745-1-zhengyejian1@huawei.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpeml500012.china.huawei.com (7.185.36.15) ftrace_location() was changed to not only return the __fentry__ location when called for the __fentry__ location, but also when called for the sym+0 location after commit aebfd12521d9 ("x86/ibt,ftrace: Search for __fentry__ location"). That is, if sym+0 location is not __fentry__, ftrace_location() would find one over the entire size of the sym. However, there is case that more than one __fentry__ exist in the sym range (described below) and ftrace_location() would find wrong __fentry__ location by binary searching, which would cause its users like livepatch/ kprobe/bpf to not work properly on this sym! The case is that, based on current compiler behavior, suppose: - function A is followed by weak function B1 in same binary file; - weak function B1 is overridden by function B2; Then in the final binary file: - symbol B1 will be removed from symbol table while its instructions are not removed; - __fentry__ of B1 will be still in __mcount_loc table; - function size of A is computed by substracting the symbol address of A from its next symbol address (see kallsyms_lookup_size_offset()), but because symbol info of B1 is removed, the next symbol of A is originally the next symbol of B1. See following example, function sizeof A will be (symbol_address_C - symbol_address_A): symbol_address_A symbol_address_B1 (Not in symbol table) symbol_address_C The weak function issue has been discovered in commit b39181f7c690 ("ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak function") but it didn't resolve the issue in ftrace_location(). Peter suggested to use entry size for FUNC type objects to find holes in the text and fill them with a symbol, then check the mcount locations against the symbol table and for every one that falls in a hole [1] [2]. What the patch set does is described as follows: - Patch 1: Do an optimization for scripts/kallsym.c about memory allocation when read symbols from file. This patch has little to do with the above issue, but since I changed this script, so it also can be reviewed here; - Patch 2: Change scripts/kallsyms.c to emit a symbol where there is a hole in the text, the symbol name is temporarily named "__hole_symbol_XXXXX"; - Patch 3: When lookup symbols in module, use entry size info to determine the exact boundaries of a function symbol; - Patch 4: Holes in text have been found in previous patches, now check __fentry__ in mcount table and skip those locate in the holes; - Patch 5: Accidentally found a out-of-bound issue when all __fentry__ are skipped, so fix it; - Patch 6: Revert Steve's patch about the FTRACE_MCOUNT_MAX_OFFSET solution, also two related definition for powerpc. [1] https://lore.kernel.org/all/20240607150228.GR8774@noisy.programming.kicks-ass.net/ [2] https://lore.kernel.org/all/20240611092157.GU40213@noisy.programming.kicks-ass.net/ Zheng Yejian (6): kallsyms: Optimize multiple times of realloc() to one time of malloc() kallsyms: Emit symbol at the holes in the text module: kallsyms: Determine exact function size ftrace: Skip invalid __fentry__ in ftrace_process_locs() ftrace: Fix possible out-of-bound issue in ftrace_process_locs() ftrace: Revert the FTRACE_MCOUNT_MAX_OFFSET workaround arch/powerpc/include/asm/ftrace.h | 7 -- arch/x86/include/asm/ftrace.h | 7 -- include/linux/kallsyms.h | 13 +++ include/linux/module.h | 14 +++ kernel/module/kallsyms.c | 42 ++++++-- kernel/trace/ftrace.c | 174 ++++++------------------------ scripts/kallsyms.c | 134 ++++++++++++++++++++--- scripts/link-vmlinux.sh | 4 +- scripts/mksysmap | 2 +- 9 files changed, 216 insertions(+), 181 deletions(-)