linux-kernel - Re: [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <14D6DBA0-0572-44FB-A566-464B1FF541E0@fb.com>
Date:   Fri, 5 Aug 2022 05:29:51 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "naveen.n.rao@...ux.ibm.com" <naveen.n.rao@...ux.ibm.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "anil.s.keshavamurthy@...el.com" <anil.s.keshavamurthy@...el.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc_exec which
 allocates RO+X memory

Hi Peter,

> On Jul 13, 2022, at 3:20 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 

[...]

> 
> So how about instead we separate them? Then much of the problem goes
> away, you don't need to track these 2M chunks at all.
> 
> Start by adding VM_TOPDOWN_VMAP, which instead of returning the lowest
> (leftmost) vmap_area that fits, picks the higests (rightmost).
> 
> Then add module_alloc_data() that uses VM_TOPDOWN_VMAP and make
> ARCH_WANTS_MODULE_DATA_IN_VMALLOC use that instead of vmalloc (with a
> weak function doing the vmalloc).
> 
> This gets you bottom of module range is RO+X only, top is shattered
> between different !X types.
> 
> Then track the boundary between X and !X and ensure module_alloc_data()
> and module_alloc() never cross over and stay strictly separated.
> 
> Then change all module_alloc() users to expect RO+X memory, instead of
> RW.
> 
> Then make sure any extention of the X range is 2M aligned.
> 
> And presto, *everybody* always uses 2M TLB for text, modules, bpf,
> ftrace, the lot and nobody is tracking chunks.
> 
> Maybe migration can be eased by instead providing module_alloc_text()
> and ARCH_WANTS_MODULE_ALLOC_TEXT.

I finally got some time to look into the code. A few questions:

1. AFAICT, vmap_area tree only works with PAGE_SIZE aligned addresses. 
   For the sharing to be more efficient, I think we need to go with
   smaller granularity. Will this work? Shall we pick a smaller 
   granularity, say 64 bytes? Or shall we go all the way to 1 byte?

2. I think we will need multiple vmap_area's sharing the same vm_struct. 
   Do we need to add refcount to vm_struct?

Thanks,
Song