From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from www62.your-server.de ([213.133.104.62]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jZ1Gt-0004m4-UF for linux-um@lists.infradead.org; Wed, 13 May 2020 23:58:45 +0000 Subject: Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe References: <20200513160038.2482415-1-hch@lst.de> <20200513160038.2482415-12-hch@lst.de> <20200513192804.GA30751@lst.de> <0c1a7066-b269-9695-b94a-bb5f4f20ebd8@iogearbox.net> <20200513232816.GZ23230@ZenIV.linux.org.uk> From: Daniel Borkmann Message-ID: <866cbe54-a027-04eb-65db-c6423d16b924@iogearbox.net> Date: Thu, 14 May 2020 01:58:33 +0200 MIME-Version: 1.0 In-Reply-To: <20200513232816.GZ23230@ZenIV.linux.org.uk> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Al Viro Cc: bpf@vger.kernel.org, linux-parisc@vger.kernel.org, Netdev , the arch/x86 maintainers , linux-um , Alexei Starovoitov , Linux Kernel Mailing List , Linux-MM , Masami Hiramatsu , Andrew Morton , bgregg@netflix.com, Linus Torvalds , Christoph Hellwig On 5/14/20 1:28 AM, Al Viro wrote: > On Thu, May 14, 2020 at 12:36:28AM +0200, Daniel Borkmann wrote: > >>> So on say s390 TASK_SIZE_USUALLy is (-PAGE_SIZE), which means we'd alway >>> try the user copy first, which seems odd. >>> >>> I'd really like to here from the bpf folks what the expected use case >>> is here, and if the typical argument is kernel or user memory. >> >> It's used for both. Given this is enabled on pretty much all program types, my >> assumption would be that usage is still more often on kernel memory than user one. > > Then it needs an argument telling it which one to use. Look at sparc64. > Or s390. Or parisc. Et sodding cetera. > > The underlying model is that the kernel lives in a separate address space. > Yes, on x86 it's actually sharing the page tables with userland, but that's > not universal. The same address can be both a valid userland one _and_ > a valid kernel one. You need to tell which one do you want. Yes, see also 6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel} and probe_read_{user, kernel}_str helpers"), and my other reply wrt bpf_trace_printk() on how to address this. All I'm trying to say is that both bpf_probe_read() and bpf_trace_printk() do exist in this form since early [e]bpf days for ~5yrs now and while broken on non-x86 there are a lot of users on x86 for this in the wild, so they need to have a chance to migrate over to the new facilities before they are fully removed. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um