linux-kernel - Re: [PATCH V2] x86/ftrace: Make sure that ftrace trampolines are not RWX

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Message-Id: <20170526092716.GA14849@osiris>
Date:   Fri, 26 May 2017 11:27:16 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH V2] x86/ftrace: Make sure that ftrace trampolines are not
 RWX

On Fri, May 26, 2017 at 09:03:13AM +0200, Thomas Gleixner wrote:
> > It seems like it really should. That would put it in a single place
> > and avoid this mistake again in the future. Does module_memfree() have
> > access to the allocation size, or does that need to get plumbed?
> 
> No, it doesn't. But the number of instances is pretty limited.
> 
> Btw, looking at BPF. It allocates memory via module_alloc() which means
> it's RWX. There is nothing in that BPF code which changes the permissions
> afterwards ....

For BPF you're probably referring to bpf_jit_binary_alloc()? Permissions
are changed with bpf_jit_binary_lock_ro() within each architecure backend.

Well, except for powerpc (cc'ed Michael).