From mboxrd@z Thu Jan 1 00:00:00 1970 From: daniel@iogearbox.net (Daniel Borkmann) Date: Fri, 17 Aug 2018 20:30:16 +0200 Subject: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on 4.18rc1 In-Reply-To: <20180817161743.GX30658@n2100.armlinux.org.uk> References: <7ff516fd-1d01-4d7a-1d5d-b58932c0c69d@gmail.com> <20180816203515.GA7688@torres.zugschlus.de> <20180816225844.GW30658@n2100.armlinux.org.uk> <1c2218cb-63bf-1528-6156-8ce93f46169c@iogearbox.net> <20180817161743.GX30658@n2100.armlinux.org.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 08/17/2018 06:17 PM, Russell King - ARM Linux wrote: > On Fri, Aug 17, 2018 at 02:40:19PM +0200, Daniel Borkmann wrote: >> I'd have one potential bug suspicion, for the 4.18 one you were trying, >> could you run with the below patch to see whether it would help? > > I think this is almost certainly the problem - looking at the history, > it seems that the "-4" was assumed to be part of the scratch stuff in > commit 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space") > but it isn't - it's because "off" of zero refers to the top word in the > stack (iow at STACK_SIZE-4). Yeah agree, my thinking as well (albeit bit late, sigh, sorry about that). Waiting for Peter to get back with results for definite confirmation. Your rework in 1c35ba122d4a ("ARM: net: bpf: use negative numbers for stacked registers") and 96cced4e774a ("ARM: net: bpf: access eBPF scratch space using ARM FP register") fixes this in mainline, so unless I'm missing something this would only need a stand-alone fix for 4.18/stable which I can cook up and submit then. Thanks, Daniel