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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c4-20020a170902f30400b001a0492c419csi9194127ple.523.2023.04.03.23.03.06; Mon, 03 Apr 2023 23:03:18 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@joshtriplett.org header.s=fm1 header.b=TVQd44oY; dkim=pass header.i=@messagingengine.com header.s=fm2 header.b=trYbBXo4; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233557AbjDDGAb (ORCPT + 99 others); Tue, 4 Apr 2023 02:00:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233184AbjDDGA3 (ORCPT ); Tue, 4 Apr 2023 02:00:29 -0400 Received: from wout2-smtp.messagingengine.com (wout2-smtp.messagingengine.com [64.147.123.25]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 455711992 for ; Mon, 3 Apr 2023 23:00:27 -0700 (PDT) Received: from compute2.internal (compute2.nyi.internal [10.202.2.46]) by mailout.west.internal (Postfix) with ESMTP id B8082320096F; Tue, 4 Apr 2023 02:00:25 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute2.internal (MEProxy); Tue, 04 Apr 2023 02:00:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= joshtriplett.org; h=cc:content-type:content-type:date:date:from :from:in-reply-to:message-id:mime-version:reply-to:sender :subject:subject:to:to; s=fm1; t=1680588025; x=1680674425; bh=Lr TlRnC1PMOEduoHyaDrJIwpQILB4R4Y2q12p1O1Lq4=; b=TVQd44oYV/EGE32s1j U2FtduT+QMuANL8y4onAgbmKKMM/FqVE0EImoq9XSjzYsMgl97KwCFjN1tNKNNig cWqI/KOygYxL3q5YAkffb9TL6FDpM58aLSeCiQAW8j2YeDeN/4pD8dZev1OvueCu 6z6eQH9PdG19ABcWHXZNVhvqRl6NN3bRJsO6GCKXq61Hw0t0f+fqg0BWaOmCjhNf TWiNCElsY/dZsI91vE8Fe0rBnANoYdv2EQxoWMUWUtnoT+g2kDNTDtyoJN3TWuXg BlanORl+lotAHUArBd/stRjGPHRBLFpEme6U4xP9nqlb35GkYO+RBPj0LEof8Vnn 7UTw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:content-type:date:date :feedback-id:feedback-id:from:from:in-reply-to:message-id :mime-version:reply-to:sender:subject:subject:to:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm2; t= 1680588025; x=1680674425; bh=LrTlRnC1PMOEduoHyaDrJIwpQILB4R4Y2q1 2p1O1Lq4=; b=trYbBXo4nZv9yYGIl660K02BlRjcUspug0z0uEJXchR0X3vVizm CWYp2aspxKTqM9H3SIhFZujUCmPiTQtnw16Ur6xG0fqdcWN9ts+KJViNLM2/c9Qj KHkZNxx0rH7DkboOcSTCxPB7zordka1C1toU/ffxhO0jGDOoq2AQQDRvCGy3mQHd o9GUutruWvP0B2SncJ5QjfMlvHMKlR2s/LQhCK+6ze9IlDFQQmF/a7eg6FguHT4c vaM2d9NaKnP2+OuZLOS9eCkmy18L7pwaXaMby59Mk4IZtnuLFQndsj6VnRkbdWsh FzrkGS0XNPKV/TbNOyiEkfzNRG3LyGN5XBw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrvdeikedgkeehucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucenucfjughrpeffhffvuffkgggtugesthdtredttd dtvdenucfhrhhomheplfhoshhhucfvrhhiphhlvghtthcuoehjohhshhesjhhoshhhthhr ihhplhgvthhtrdhorhhgqeenucggtffrrghtthgvrhhnpeelleeggedtjeejfeeuvddufe eggfektdefkeehveeuvedvvdfhgeffgfdvgfffkeenucevlhhushhtvghrufhiiigvpedt necurfgrrhgrmhepmhgrihhlfhhrohhmpehjohhshhesjhhoshhhthhrihhplhgvthhtrd horhhg X-ME-Proxy: Feedback-ID: i83e94755:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 4 Apr 2023 02:00:23 -0400 (EDT) Date: Tue, 4 Apr 2023 15:00:19 +0900 From: Josh Triplett To: Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH] prctl: Add PR_GET_AUXV to copy auxv to userspace Message-ID: MIME-Version: 1.0 Content-Disposition: inline X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,RCVD_IN_MSPIKE_H2, SPF_HELO_PASS,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1762224450914062793?= X-GMAIL-MSGID: =?utf-8?q?1762224450914062793?= If a library wants to get information from auxv (for instance, AT_HWCAP/AT_HWCAP2), it has a few options, none of them perfectly reliable or ideal: - Be main or the pre-main startup code, and grub through the stack above main. Doesn't work for a library. - Call libc getauxval. Not ideal for libraries that are trying to be libc-independent and/or don't otherwise require anything from other libraries. - Open and read /proc/self/auxv. Doesn't work for libraries that may run in arbitrarily constrained environments that may not have /proc mounted (e.g. libraries that might be used by an init program or a container setup tool). - Assume you're on the main thread and still on the original stack, and try to walk the stack upwards, hoping to find auxv. Extremely bad idea. - Ask the caller to pass auxv in for you. Not ideal for a user-friendly library, and then your caller may have the same problem. Add a prctl that copies current->mm->saved_auxv to a userspace buffer. Signed-off-by: Josh Triplett --- I've built, booted, and tested this. man-pages snippet: .\" prctl PR_GET_AUXV .TP .BR PR_GET_AUXV " (since Linux 6.x)" Get the auxilliary vector (auxv) into the buffer pointed to by .IR "(void\~*) arg2" , whose length is given by \fIarg3\fP. If the buffer is not long enough for the full auxilliary vector, the copy will be truncated. Return (as the function result) the full length of the auxilliary vector. \fIarg4\fP and \fIarg5\fP must be 0. Will send a patch for man-pages once merged. include/uapi/linux/prctl.h | 2 ++ kernel/sys.c | 15 +++++++++++++++ 2 files changed, 17 insertions(+) diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 1312a137f7fb..b2b24eaf2427 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -290,4 +290,6 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +#define PR_GET_AUXV 0x41555856 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 495cd87d9bf4..fdd297507d7e 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2377,6 +2377,16 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3, PR_MDWE_REFUSE_EXEC_GAIN : 0; } +static int prctl_get_auxv(void __user *addr, unsigned long len) +{ + struct mm_struct *mm = current->mm; + unsigned long size = min(sizeof(mm->saved_auxv), len); + + if (size && copy_to_user(addr, mm->saved_auxv, size)) + return -EFAULT; + return sizeof(mm->saved_auxv); +} + SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, unsigned long, arg4, unsigned long, arg5) { @@ -2661,6 +2671,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; + case PR_GET_AUXV: + if (arg4 || arg5) + return -EINVAL; + error = prctl_get_auxv((void __user *)arg2, arg3); + break; default: error = -EINVAL; break;