From: Masami Hiramatsu <mhiramat@kernel.org>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: akpm@linux-foundation.org, luto@kernel.org, will.deacon@arm.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com,
naveen.n.rao@linux.vnet.ibm.com, anil.s.keshavamurthy@intel.com,
davem@davemloft.net, rostedt@goodmis.org, mingo@redhat.com,
ast@kernel.org, daniel@iogearbox.net, jeyu@kernel.org,
netdev@vger.kernel.org, ard.biesheuvel@linaro.org,
jannh@google.com, kristen@linux.intel.com, dave.hansen@intel.com,
deneen.t.dock@intel.com
Subject: Re: [PATCH 0/2] Don’t leave executable TLB entries to freed pages
Date: Thu, 29 Nov 2018 23:06:16 +0900 [thread overview]
Message-ID: <20181129230616.f017059a093841dbaa4b82e6@kernel.org> (raw)
In-Reply-To: <20181128000754.18056-1-rick.p.edgecombe@intel.com>
On Tue, 27 Nov 2018 16:07:52 -0800
Rick Edgecombe <rick.p.edgecombe@intel.com> wrote:
> Sometimes when memory is freed via the module subsystem, an executable
> permissioned TLB entry can remain to a freed page. If the page is re-used to
> back an address that will receive data from userspace, it can result in user
> data being mapped as executable in the kernel. The root of this behavior is
> vfree lazily flushing the TLB, but not lazily freeing the underlying pages.
Good catch!
>
> There are sort of three categories of this which show up across modules, bpf,
> kprobes and ftrace:
For x86-64 kprobe, it sets the page NX and after that RW, and then release
via module_memfree. So I'm not sure it really happens on kprobes. (Of course
the default memory allocator is simpler so it may happen on other archs) But
interesting fixes.
Thank you,
>
> 1. When executable memory is touched and then immediatly freed
>
> This shows up in a couple error conditions in the module loader and BPF JIT
> compiler.
>
> 2. When executable memory is set to RW right before being freed
>
> In this case (on x86 and probably others) there will be a TLB flush when its
> set to RW and so since the pages are not touched between setting the
> flush and the free, it should not be in the TLB in most cases. So this
> category is not as big of a concern. However, techinically there is still a
> race where an attacker could try to keep it alive for a short window with a
> well timed out-of-bound read or speculative read, so ideally this could be
> blocked as well.
>
> 3. When executable memory is freed in an interrupt
>
> At least one example of this is the freeing of init sections in the module
> loader. Since vmalloc reuses the allocation for the work queue linked list
> node for the deferred frees, the memory actually gets touched as part of the
> vfree operation and so returns to the TLB even after the flush from resetting
> the permissions.
>
> I have only actually tested category 1, and identified 2 and 3 just from reading
> the code.
>
> To catch all of these, module_alloc for x86 is changed to use a new flag that
> instructs the unmap operation to flush the TLB before freeing the pages.
>
> If this solution seems good I can plug the flag in for other architectures that
> define PAGE_KERNEL_EXEC.
>
>
> Rick Edgecombe (2):
> vmalloc: New flag for flush before releasing pages
> x86/modules: Make x86 allocs to flush when free
>
> arch/x86/kernel/module.c | 4 ++--
> include/linux/vmalloc.h | 1 +
> mm/vmalloc.c | 13 +++++++++++--
> 3 files changed, 14 insertions(+), 4 deletions(-)
>
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2018-11-29 14:06 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
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 [this message]
2018-11-29 18:49 ` Edgecombe, Rick P
2018-11-29 23:19 ` Masami Hiramatsu
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