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Date: Thu, 21 Jan 2016 23:57:41 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Josh Poimboeuf <jpoimboe@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org CC: linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, Michal Marek <mmarek@...e.cz>, Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <andi@...stfloor.org>, Pedro Alves <palves@...hat.com>, Namhyung Kim <namhyung@...il.com>, Bernd Petrovitsch <bernd@...rovitsch.priv.at>, Chris J Arges <chris.j.arges@...onical.com>, Andrew Morton <akpm@...ux-foundation.org>, Jiri Slaby <jslaby@...e.cz>, Arnaldo Carvalho de Melo <acme@...nel.org>, Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org Subject: Re: [PATCH 31/33] bpf: Add __bpf_prog_run() to stacktool whitelist On 01/21/2016 11:49 PM, Josh Poimboeuf wrote: > stacktool reports the following false positive warnings: > > stacktool: kernel/bpf/core.o: __bpf_prog_run()+0x5c: sibling call from callable instruction with changed frame pointer > stacktool: kernel/bpf/core.o: __bpf_prog_run()+0x60: function has unreachable instruction > stacktool: kernel/bpf/core.o: __bpf_prog_run()+0x64: function has unreachable instruction > [...] > > It's confused by the following dynamic jump instruction in > __bpf_prog_run():: > > jmp *(%r12,%rax,8) > > which corresponds to the following line in the C code: > > goto *jumptable[insn->code]; > > There's no way for stacktool to deterministically find all possible > branch targets for a dynamic jump, so it can't verify this code. > > In this case the jumps all stay within the function, and there's nothing > unusual going on related to the stack, so we can whitelist the function. > > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com> > Cc: Alexei Starovoitov <ast@...nel.org> > Cc: netdev@...r.kernel.org Fine by me: Acked-by: Daniel Borkmann <daniel@...earbox.net>
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