linux-kernel - Re: [PATCH v2 1/7] modules: Create rlimit for module space

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Message-ID: <CAG48ez383rjt+v_DvLF902X33od_SwMh8dZ-6=w1DZ-YPZ_U9Q@mail.gmail.com>
Date:   Sat, 13 Oct 2018 02:09:09 +0200
From:   Jann Horn <jannh@...gle.com>
To:     rick.p.edgecombe@...el.com
Cc:     linux-fsdevel@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>, jeyu@...nel.org,
        Arjan van de Ven <arjan@...ux.intel.com>,
        linux-mips@...ux-mips.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-s390 <linux-s390@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kristen@...ux.intel.com, deneen.t.dock@...el.com,
        Catalin Marinas <catalin.marinas@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        "David S. Miller" <davem@...emloft.net>,
        linux-arch <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, sparclinux@...r.kernel.org
Subject: Re: [PATCH v2 1/7] modules: Create rlimit for module space

On Sat, Oct 13, 2018 at 2:04 AM Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
> On Fri, 2018-10-12 at 19:22 +0200, Jann Horn wrote:
> > On Fri, Oct 12, 2018 at 7:04 PM Edgecombe, Rick P
> > <rick.p.edgecombe@...el.com> wrote:
> > > On Fri, 2018-10-12 at 02:35 +0200, Jann Horn wrote:
> > > > Why all the rbtree stuff instead of stashing a pointer in struct
> > > > vmap_area, or something like that?
> > >
> > > Since the tracking was not for all vmalloc usage, the intention was to not
> > > bloat
> > > the structure for other usages likes stacks. I thought usually there
> > > wouldn't be
> > > nearly as much module space allocations as there would be kernel stacks, but
> > > I
> > > didn't do any actual measurements on the tradeoffs.
> >
> > I imagine that one extra pointer in there - pointing to your struct
> > mod_alloc_user - would probably not be terrible. 8 bytes more per
> > kernel stack shouldn't be so bad?
>
> I looked into this and it starts to look a little messy. The nommu.c version of
> vmalloc doesn't use or expose access to vmap_area or vm_struct. So it starts to
> look like a bunch of IFDEFs to remove the rlimit in the nommu case or making a
> stand in that maintains pretend vm struct's in nommu.c. I had actually
> previously tried to at least pull the allocations size from vmalloc structs, but it broke on nommu.
>
> Thought I would check back and see. How important do you think this is?

I don't think it's important - I just thought that it would be nice to
avoid the extra complexity if it is easily avoidable.