From: Andy Lutomirski <luto@kernel.org>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Andrew Lutomirski <luto@kernel.org>,
Tycho Andersen <tycho@tycho.ws>,
LKML <linux-kernel@vger.kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Alexei Starovoitov <ast@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Jessica Yu <jeyu@kernel.org>, Linux-MM <linux-mm@kvack.org>,
Jann Horn <jannh@google.com>, Nadav Amit <nadav.amit@gmail.com>,
"Dock, Deneen T" <deneen.t.dock@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@redhat.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
"Naveen N . Rao" <naveen.n.rao@linux.vnet.ibm.com>,
"David S. Miller" <davem@davemloft.net>,
Network Development <netdev@vger.kernel.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages
Date: Thu, 6 Dec 2018 12:26:18 -0800 [thread overview]
Message-ID: <CALCETrUzHzQWTW8ZAz0jL6BA2KmnBPBod8a3oYuwiEhbL98WtQ@mail.gmail.com> (raw)
In-Reply-To: <f6096b80bdab59d2d21ece4ff31fcfd36bf6b809.camel@intel.com>
On Thu, Dec 6, 2018 at 12:20 PM Edgecombe, Rick P
<rick.p.edgecombe@intel.com> wrote:
>
> On Thu, 2018-12-06 at 11:19 -0800, Andy Lutomirski wrote:
> > On Thu, Dec 6, 2018 at 11:01 AM Tycho Andersen <tycho@tycho.ws> wrote:
> > >
> > > On Thu, Dec 06, 2018 at 10:53:50AM -0800, Andy Lutomirski wrote:
> > > > > If we are going to unmap the linear alias, why not do it at vmalloc()
> > > > > time rather than vfree() time?
> > > >
> > > > That’s not totally nuts. Do we ever have code that expects __va() to
> > > > work on module data? Perhaps crypto code trying to encrypt static
> > > > data because our APIs don’t understand virtual addresses. I guess if
> > > > highmem is ever used for modules, then we should be fine.
> > > >
> > > > RO instead of not present might be safer. But I do like the idea of
> > > > renaming Rick's flag to something like VM_XPFO or VM_NO_DIRECT_MAP and
> > > > making it do all of this.
> > >
> > > Yeah, doing it for everything automatically seemed like it was/is
> > > going to be a lot of work to debug all the corner cases where things
> > > expect memory to be mapped but don't explicitly say it. And in
> > > particular, the XPFO series only does it for user memory, whereas an
> > > additional flag like this would work for extra paranoid allocations
> > > of kernel memory too.
> > >
> >
> > I just read the code, and I looks like vmalloc() is already using
> > highmem (__GFP_HIGH) if available, so, on big x86_32 systems, for
> > example, we already don't have modules in the direct map.
> >
> > So I say we go for it. This should be quite simple to implement --
> > the pageattr code already has almost all the needed logic on x86. The
> > only arch support we should need is a pair of functions to remove a
> > vmalloc address range from the address map (if it was present in the
> > first place) and a function to put it back. On x86, this should only
> > be a few lines of code.
> >
> > What do you all think? This should solve most of the problems we have.
> >
> > If we really wanted to optimize this, we'd make it so that
> > module_alloc() allocates memory the normal way, then, later on, we
> > call some function that, all at once, removes the memory from the
> > direct map and applies the right permissions to the vmalloc alias (or
> > just makes the vmalloc alias not-present so we can add permissions
> > later without flushing), and flushes the TLB. And we arrange for
> > vunmap to zap the vmalloc range, then put the memory back into the
> > direct map, then free the pages back to the page allocator, with the
> > flush in the appropriate place.
> >
> > I don't see why the page allocator needs to know about any of this.
> > It's already okay with the permissions being changed out from under it
> > on x86, and it seems fine. Rick, do you want to give some variant of
> > this a try?
> Hi,
>
> Sorry, I've been having email troubles today.
>
> I found some cases where vmap with PAGE_KERNEL_RO happens, which would not set
> NP/RO in the directmap, so it would be sort of inconsistent whether the
> directmap of vmalloc range allocations were readable or not. I couldn't see any
> places where it would cause problems today though.
>
> I was ready to assume that all TLBs don't cache NP, because I don't know how
> usages where a page fault is used to load something could work without lots of
> flushes.
Or the architecture just fixes up the spurious faults, I suppose. I'm
only well-educated on the x86 mmu.
> If that's the case, then all archs with directmap permissions could
> share a single vmalloc special permission flush implementation that works like
> Andy described originally. It could be controlled with an
> ARCH_HAS_DIRECT_MAP_PERMS. We would just need something like set_pages_np and
> set_pages_rw on any archs with directmap permissions. So seems simpler to me
> (and what I have been doing) unless I'm missing the problem.
Hmm. The only reason I've proposed anything fancier was because I was
thinking of minimizing flushes, but I think I'm being silly. This
sequence ought to work optimally:
- vmalloc(..., VM_HAS_DIRECT_MAP_PERMS); /* no flushes */
- Write some data, via vmalloc's return address.
- Use some set_memory_whatever() functions to update permissions,
which will flush, hopefully just once.
- Run the module code!
- vunmap -- this will do a single flush that will fix everything.
This does require that set_pages_np() or set_memory_np() or whatever
exists and that it's safe to do that, then flush, and then
set_pages_rw(). So maybe you want set_pages_np_noflush() and
set_pages_rw_noflush() to make it totally clear what's supposed to
happen.
--Andy
next prev parent reply other threads:[~2018-12-06 20:26 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 0:07 [PATCH 0/2] Don’t leave executable TLB entries to freed pages Rick Edgecombe
2018-11-28 0:07 ` [PATCH 1/2] vmalloc: New flag for flush before releasing pages Rick Edgecombe
2018-12-04 0:04 ` Edgecombe, Rick P
2018-12-04 1:43 ` Nadav Amit
2018-12-04 16:03 ` Will Deacon
2018-12-04 20:02 ` Edgecombe, Rick P
2018-12-04 20:09 ` Andy Lutomirski
2018-12-04 23:52 ` Edgecombe, Rick P
2018-12-05 1:57 ` Andy Lutomirski
2018-12-05 11:41 ` Will Deacon
2018-12-05 23:16 ` Andy Lutomirski
2018-12-06 7:29 ` Ard Biesheuvel
2018-12-06 11:10 ` Will Deacon
2018-12-06 18:53 ` Andy Lutomirski
2018-12-06 19:01 ` Tycho Andersen
2018-12-06 19:19 ` Andy Lutomirski
2018-12-06 19:39 ` Nadav Amit
2018-12-06 20:17 ` Andy Lutomirski
2018-12-06 23:08 ` Nadav Amit
2018-12-07 3:06 ` Edgecombe, Rick P
2018-12-06 20:19 ` Edgecombe, Rick P
2018-12-06 20:26 ` Andy Lutomirski [this message]
2018-12-06 19:04 ` Ard Biesheuvel
2018-12-06 19:20 ` Andy Lutomirski
2018-12-06 19:23 ` Ard Biesheuvel
2018-12-06 19:31 ` Will Deacon
2018-12-06 19:36 ` Ard Biesheuvel
2018-12-04 20:36 ` Nadav Amit
[not found] ` <e70c618d10ddbb834b7a3bbdd6e2bebed0f8719d.camel@intel.com>
2018-12-05 0:01 ` Nadav Amit
2018-12-05 0:29 ` Edgecombe, Rick P
2018-12-05 0:53 ` Nadav Amit
2018-12-05 1:45 ` Edgecombe, Rick P
2018-12-05 2:09 ` Nadav Amit
2018-12-04 18:56 ` Andy Lutomirski
2018-12-04 19:44 ` Nadav Amit
2018-12-04 19:48 ` Andy Lutomirski
2018-12-04 22:48 ` Nadav Amit
2018-12-04 23:27 ` Andy Lutomirski
2018-12-04 23:34 ` Nadav Amit
2018-12-05 1:09 ` Edgecombe, Rick P
2018-12-05 1:45 ` Nadav Amit
2018-11-28 0:07 ` [PATCH 2/2] x86/modules: Make x86 allocs to flush when free Rick Edgecombe
2018-11-28 23:11 ` Andrew Morton
2018-11-29 0:02 ` Edgecombe, Rick P
2018-11-29 1:40 ` Andy Lutomirski
2018-11-29 6:14 ` Edgecombe, Rick P
2018-11-28 1:06 ` [PATCH 0/2] Don’t leave executable TLB entries to freed pages Nadav Amit
2018-11-28 1:21 ` Nadav Amit
2018-11-28 9:57 ` Will Deacon
2018-11-28 18:29 ` Nadav Amit
2018-11-29 14:06 ` Masami Hiramatsu
2018-11-29 18:49 ` Edgecombe, Rick P
2018-11-29 23:19 ` Masami Hiramatsu
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