linux-kernel - Re: [PATCH 0/2] Don’t leave executable TLB entries to freed pages

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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, luto@...nel.org, will.deacon@....com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        naveen.n.rao@...ux.vnet.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, mhiramat@...nel.org, rostedt@...dmis.org,
        mingo@...hat.com, ast@...nel.org, daniel@...earbox.net,
        jeyu@...nel.org, netdev@...r.kernel.org, ard.biesheuvel@...aro.org,
        jannh@...gle.com, kristen@...ux.intel.com, dave.hansen@...el.com,
        deneen.t.dock@...el.com
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.