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Date: Tue, 27 Nov 2018 17:06:05 -0800
From: Nadav Amit <>
To: Rick Edgecombe <>
Subject: Re: [PATCH 0/2] Don’t leave executable TLB entries to freed pages

> On Nov 27, 2018, at 4:07 PM, Rick Edgecombe <> 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.


Note that this may cause conflict with "x86: avoid W^X being broken during
modules loading”, which I recently submitted.

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