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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c4-20020a621c04000000b00625c2bd736asi10750426pfc.20.2023.04.04.05.36.33; Tue, 04 Apr 2023 05:36:46 -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=ekmuq8zk; dkim=pass header.i=@messagingengine.com header.s=fm2 header.b="TelJz/PP"; 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 S234858AbjDDMb6 (ORCPT + 99 others); Tue, 4 Apr 2023 08:31:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231344AbjDDMb5 (ORCPT ); Tue, 4 Apr 2023 08:31:57 -0400 Received: from wout3-smtp.messagingengine.com (wout3-smtp.messagingengine.com [64.147.123.19]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37DE3170C for ; Tue, 4 Apr 2023 05:31:55 -0700 (PDT) Received: from compute6.internal (compute6.nyi.internal [10.202.2.47]) by mailout.west.internal (Postfix) with ESMTP id 7FAEF3200934; Tue, 4 Apr 2023 08:31:54 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute6.internal (MEProxy); Tue, 04 Apr 2023 08:31:54 -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=1680611514; x=1680697914; bh=nt 6QuxRluVizW8uPZoCJ4NC8q9XQ4kfvc7TVTu/KcJw=; b=ekmuq8zkGHbLBYey+c 1XMecsdG2y9co0x62WU2T2zlddxfC976rXhIjQynILiMPq1jxI9RFHmdcaaWf06A 0NT61BrlAkFGCNzhM1pb8aW7vnk599VrAgTgXr8STZcdN8sZg5OuznQoCsxznUjN nVoRQo+Fx+JpLQ9v6UZpMuN8JbgpXQml4O8rr9ceuAc9D7sEo7MrCJ0TZfIEYq2U lquCMu2Y+8hni7kuv53j6vX/UxRHu/u+LCdWaC0CGK2nvxuvw+fJoDtXgrv5blhd NTG74N5qr8KfM4T2nTsSySWlRmQsLSRv+vb/L7YzYEwLTbkXBq4C2jA4lW71rqup BJYw== 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= 1680611514; x=1680697914; bh=nt6QuxRluVizW8uPZoCJ4NC8q9XQ4kfvc7T VTu/KcJw=; b=TelJz/PPtY2EeYcftDqF5K1vPxYxI1iHYy4ovtr4RgWveLbfGuj s+a1/TgvBK2uBcvvqj6yh9+WEBjvuyFu5m4NrJCFqjWFM27KIMar6b8NL2QFV87b V1VByMRcLozA0bJZ/3F9ppcOTkjGtvceXGzY0IYKfYXSIBaO+rI3kBhKct+bUumV RMcHZqnlLq3doU7aGwIfbifsow7Gi/AEqNKtlMII1FEy9pQEvEn44I9UPV2/T0Bk A+gZNX584FuL57Xpt520bcyN5LYltUSmSRQOziwm9Iy9FZgIAuoCio7OG5x5J+iS vqhwIHAmYgCNZCkoTZ8Vv84QRFI+y4ZJNSg== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrvdeiledgheefucetufdoteggodetrfdotf 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 08:31:52 -0400 (EDT) Date: Tue, 4 Apr 2023 21:31:48 +0900 From: Josh Triplett To: Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v2] 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,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?1762249205386186832?= 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 --- v2: - Fix W=1 warning about min type mismatch 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..43f922170706 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_t(unsigned long, 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;