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Message-Id: <CDB8B7C1-FD55-44AD-9B71-B3A750BF5489@gmail.com>
Date: Tue, 27 Nov 2018 17:06:05 -0800
From: Nadav Amit <nadav.amit@...il.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: akpm@...ux-foundation.org,
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Subject: Re: [PATCH 0/2] Don’t leave executable TLB entries to freed pages
> On Nov 27, 2018, at 4:07 PM, Rick Edgecombe <rick.p.edgecombe@...el.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.
>
> There are sort of three categories of this which show up across modules, bpf,
> kprobes and ftrace:
>
> 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.
Interesting!
Note that this may cause conflict with "x86: avoid W^X being broken during
modules loading”, which I recently submitted.
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