linux-kernel - Re: [PATCH v3 bpf-next 5/8] bpf: use module_alloc_huge for bpf_prog

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Message-ID: <20220525060142.GB10762@lst.de>
Date:   Wed, 25 May 2022 08:01:42 +0200
From:   "hch@....de" <hch@....de>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "hch@....de" <hch@....de>, "dave@...olabs.net" <dave@...olabs.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "kernel-team@...com" <kernel-team@...com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "song@...nel.org" <song@...nel.org>,
        "Torvalds, Linus" <torvalds@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        Adam Manzanares <a.manzanares@...sung.com>
Subject: Re: [PATCH v3 bpf-next 5/8] bpf: use module_alloc_huge for
 bpf_prog_pack

On Tue, May 24, 2022 at 03:08:12PM -0700, Luis Chamberlain wrote:
> > A rename seems good to me. Module space is really just dynamically
> > allocated text space now. There used to be a vmalloc_exec() that
> > allocated text in vmalloc space, 
> 
> Yes I saw that but it was generic and it did not do the arch-specific
> override, and so that is why Christoph ripped it out and open coded
> it on the only user, on module_alloc().

It it also because random code does not have any business allocating
executable memory.  Executable memory in kernel is basically for
modules and module-like code like eBPF, and no one else has any business
allocating pages with the execute bit set (or the NX bit not set).