From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] ARM: net: delegate filter to kernel interpreter when imm_offset() return value can't fit into 12bits. Date: Sun, 10 May 2015 19:22:17 -0400 (EDT) Message-ID: <20150510.192217.1306037281172187835.davem@davemloft.net> References: <1431011661-10277-1-git-send-email-nschichan@freebox.fr> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: linux@arm.linux.org.uk, ast@plumgrid.com, daniel@iogearbox.net, mgherzan@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: nschichan@freebox.fr Return-path: In-Reply-To: <1431011661-10277-1-git-send-email-nschichan@freebox.fr> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Nicolas Schichan Date: Thu, 7 May 2015 17:14:21 +0200 > The ARM JIT code emits "ldr rX, [pc, #offset]" to access the literal > pool. #offset maximum value is 4095 and if the generated code is too > large, the #offset value can overflow and not point to the expected > slot in the literal pool. Additionally, when overflow occurs, bits of > the overflow can end up changing the destination register of the ldr > instruction. > > Fix that by detecting the overflow in imm_offset() and setting a flag > that is checked for each BPF instructions converted in > build_body(). As of now it can only be detected in the second pass. As > a result the second build_body() call can now fail, so add the > corresponding cleanup code in that case. > > Using multiple literal pools in the JITed code is going to require > lots of intrusive changes to the JIT code (which would better be done > as a feature instead of fix), just delegating to the kernel BPF > interpreter in that case is a more straight forward, minimal fix and > easy to backport. > > Signed-off-by: Nicolas Schichan Applied, thanks Nicolas.