Subject: Re: [PATCH 31/33] bpf: Add __bpf_prog_run() to stacktool whitelist

From: Daniel Borkmann <[email-masked]>
Date: Thu, 21 Jan 2016 23:57:41 +0100

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 <[email-masked]>
> Cc: Alexei Starovoitov <[email-masked]>
> Cc: [email-masked]

Fine by me:

Acked-by: Daniel Borkmann <[email-masked]>