From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Date: Thu, 5 Sep 2019 12:57:49 +0200 Message-ID: <20190905105749.GW2386@hirez.programming.kicks-ass.net> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> <20190905073205.GY2332@hirez.programming.kicks-ass.net> <20190905092622.tlb6nn3uisssdfbu@yavin.dot.cyphar.com> <20190905094305.GJ2349@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ne0I6Jb3EBTCOHFAthZ0YWUTT79Oz59igWgXS4KJDt8=; b=P4LASZEfIY3qVP RxOe94FPj8EqkkDhZn6w+7cvCj7p1lEfEodrRXciEjChbFVkyNNWgEKUa7vf3u+2MLpPNPdAbMhvE diX11GKJp7HdCgGRkm9LC/QNyKxtMAsesda4R9Gl8DyZVKUf02SswXi9y3XVPDTD1+mIrpQUXVTkf ON+1mZ4NsoEeCi7j4lZUbkJa6UlIemJa5j3Wl5x1MYBhNl6ic2JXPRd1ZM9VRDS6cvBIjIPkE7zIP Aw0uPmYSu5GX/vOqcz8ciyHnRQYbb1yAo6pRwKFopQOPC7Mg/OS3iJfKvak42ZYvlTOAPpwpl7nX5 NVENbOX8AkQsolzdwLeA==; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=+Sinl1C05/gcXMERfRM/CU0CjBg4xK+OsBSdZDx7CWA=; b=IjEDEzxQ6IOLkFjkqA8G4weVr 2ix5c/aN4vGafnJXRf8rm/lgF5V/h8pr9d+f7e8f9OSp80GpF3zbO7SWy+3CyteSdnLqJ6Ic01Eck Qw45hjOn6CGILdH7NYdlX3QNlS6oBhbtjqOQIJ4pNdWA6KkcZlyOT+79D27wNXhjHRMhibB3VXOyP sAJWusCKmntCRiDFHFAB8StBwMoFAeeUSuWFHvMRXj5LbGacMCNuzaOlSVL9EYzyssCtUNWwPs/OK 0uzjRDmNrV/qRN36OfkME7aOIHLiHj9z0OGY4db+OtNKgaMRhA1yiHliWNZazO5KpD60UvZM6wqyK PFVlbiYIA==; Content-Disposition: inline In-Reply-To: <20190905094305.GJ2349@hirez.programming.kicks-ass.net> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Aleksa Sarai Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Alexander Shishkin , Rasmus Villemoes , Alexei Starovoitov , linux-kernel@vger.kernel.org, David Howells , linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, Jiri Olsa , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Tycho Andersen , Aleksa Sarai , Shuah Khan , Ingo Molnar , linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-xtensa@linux-xtensa.org, Kees Cook , Arnd Bergmann , Jann Horn , linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org, Al Viro , Andy Lutomirski , Shuah Khan On Thu, Sep 05, 2019 at 11:43:05AM +0200, Peter Zijlstra wrote: > On Thu, Sep 05, 2019 at 07:26:22PM +1000, Aleksa Sarai wrote: > > On 2019-09-05, Peter Zijlstra wrote: > > > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > > > > +/** > > > > + * copy_struct_to_user: copy a struct to user space > > > > + * @dst: Destination address, in user space. > > > > + * @usize: Size of @dst struct. > > > > + * @src: Source address, in kernel space. > > > > + * @ksize: Size of @src struct. > > > > + * > > > > + * Copies a struct from kernel space to user space, in a way that guarantees > > > > + * backwards-compatibility for struct syscall arguments (as long as future > > > > + * struct extensions are made such that all new fields are *appended* to the > > > > + * old struct, and zeroed-out new fields have the same meaning as the old > > > > + * struct). > > > > + * > > > > + * @ksize is just sizeof(*dst), and @usize should've been passed by user space. > > > > + * The recommended usage is something like the following: > > > > + * > > > > + * SYSCALL_DEFINE2(foobar, struct foo __user *, uarg, size_t, usize) > > > > + * { > > > > + * int err; > > > > + * struct foo karg = {}; > > > > + * > > > > + * // do something with karg > > > > + * > > > > + * err = copy_struct_to_user(uarg, usize, &karg, sizeof(karg)); > > > > + * if (err) > > > > + * return err; > > > > + * > > > > + * // ... > > > > + * } > > > > + * > > > > + * There are three cases to consider: > > > > + * * If @usize == @ksize, then it's copied verbatim. > > > > + * * If @usize < @ksize, then kernel space is "returning" a newer struct to an > > > > + * older user space. In order to avoid user space getting incomplete > > > > + * information (new fields might be important), all trailing bytes in @src > > > > + * (@ksize - @usize) must be zerored > > > > > > s/zerored/zero/, right? > > > > It should've been "zeroed". > > That reads wrong to me; that way it reads like this function must take > that action and zero out the 'rest'; which is just wrong. > > This function must verify those bytes are zero, not make them zero. > > > > > , otherwise -EFBIG is returned. > > > > > > 'Funny' that, copy_struct_from_user() below seems to use E2BIG. > > > > This is a copy of the semantics that sched_[sg]etattr(2) uses -- E2BIG for > > a "too big" struct passed to the kernel, and EFBIG for a "too big" > > struct passed to user-space. I would personally have preferred EMSGSIZE > > instead of EFBIG, but felt using the existing error codes would be less > > confusing. > > Sadly a recent commit: > > 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code") > > Made the situation even 'worse'. And thinking more about things; I'm not convinced the above patch is actually right. Do we really want to simply truncate all the attributes of the task? And should we not at least set sched_flags when there are non-default clamp values applied? See; that is I think the primary bug that had chrt failing; we tried to publish the default clamp values as !0.