From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] bpf: fix bpf_trace_printk on 32 bit archs Date: Tue, 15 Aug 2017 17:32:57 -0700 (PDT) Message-ID: <20170815.173257.21810623154828496.davem@davemloft.net> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: james.hogan@imgtec.com, ast@fb.com, netdev@vger.kernel.org To: daniel@iogearbox.net Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:44416 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752718AbdHPAc6 (ORCPT ); Tue, 15 Aug 2017 20:32:58 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Daniel Borkmann Date: Wed, 16 Aug 2017 01:45:33 +0200 > James reported that on MIPS32 bpf_trace_printk() is currently > broken while MIPS64 works fine: > > bpf_trace_printk() uses conditional operators to attempt to > pass different types to __trace_printk() depending on the > format operators. This doesn't work as intended on 32-bit > architectures where u32 and long are passed differently to > u64, since the result of C conditional operators follows the > "usual arithmetic conversions" rules, such that the values > passed to __trace_printk() will always be u64 [causing issues > later in the va_list handling for vscnprintf()]. > > For example the samples/bpf/tracex5 test printed lines like > below on MIPS32, where the fd and buf have come from the u64 > fd argument, and the size from the buf argument: > > [...] 1180.941542: 0x00000001: write(fd=1, buf= (null), size=6258688) > > Instead of this: > > [...] 1625.616026: 0x00000001: write(fd=1, buf=009e4000, size=512) > > One way to get it working is to expand various combinations > of argument types into 8 different combinations for 32 bit > and 64 bit kernels. Fix tested by James on MIPS32 and MIPS64 > as well that it resolves the issue. > > Fixes: 9c959c863f82 ("tracing: Allow BPF programs to call bpf_trace_printk()") > Reported-by: James Hogan > Tested-by: James Hogan > Signed-off-by: Daniel Borkmann Applied and queued up for -stable, thanks Daniel.