Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 17 Jan 2018 12:01:35 -0800
From: Eric Dumazet <>
To: Linus Torvalds <>
Cc: Alan Cox <>, Dan Williams <>, 
	Linux Kernel Mailing List <>,, 
	Andi Kleen <>, Kees Cook <>,, 
	Greg Kroah-Hartman <>, "the arch/x86 maintainers" <>, 
	Ingo Molnar <>, Al Viro <>, 
	"H. Peter Anvin" <>, Thomas Gleixner <>, 
	Andrew Morton <>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in
 get_user paths

On Wed, Jan 17, 2018 at 11:26 AM, Linus Torvalds
<> wrote:
> On Wed, Jan 17, 2018 at 6:17 AM, Alan Cox <> wrote:
>> Can we kill off the remaining users of set_fs() ?
> I would love to, but it's not going to happen short-term. If ever.
> Some could be removed today: the code in arch/x86/net/bpf_jit_comp.c
> seems to be literally the ramblings of a diseased mind. There's no
> reason for the set_fs(), there's no reason for the
> flush_icache_range() (it's a no-op on x86 anyway), and the smp_wmb()
> looks bogus too.
> I have no idea how that braindamage happened, but I assume it got
> copied from some broken source.

At the time commit 0a14842f5a3c0e88a1e59fac5c3025db39721f74 went in,
this was the first JIT implementation for BPF, so maybe I wanted to avoid
other arches to forget to flush icache : You bet that my implementation served
as a reference for other JIT.

At that time, various calls to flush_icache_range() were definitely in arch/x86
or kernel/module.c

(I believe I must have copied the code from kernel/module.c, but that
I am not sure)

> But there are about ~100 set_fs() calls in generic code, and some of
> those really are pretty fundamental. Doing things like "kernel_read()"
> without set_fs() is basically impossible.
> We've had set_fs() since the beginning. The naming is obviously very
> historical. We have it for a very good reason, and I don't really see
> that reason going away.
> So realistically, we want to _minimize_ set_fs(), and we might want to
> make sure that it's done only in limited settings (it might, for
> example, be a good idea and a realistic goal to make sure that drivers
> and modules can't do it, and use proper helper functions like that
> "read_kernel()").
> But getting rid of the concept entirely? Doesn't seem likely.
>              Linus

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.