linux-kernel - Prevent inconsistent CPU state after sequence of dlclose/dlopen

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Message-ID: <c606fd39-e835-44a6-a9be-9c6fab3c48fd@efficios.com>
Date: Fri, 10 Jan 2025 10:55:36 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: libc-alpha <libc-alpha@...rceware.org>
Cc: Florian Weimer <fweimer@...hat.com>, "carlos@...hat.com"
 <carlos@...hat.com>, Mark Rutland <mark.rutland@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 linux-kernel <linux-kernel@...r.kernel.org>, x86@...nel.org,
 paulmck <paulmck@...nel.org>, Michael Jeanson <mjeanson@...icios.com>
Subject: Prevent inconsistent CPU state after sequence of dlclose/dlopen

Hi,

I was discussing with Mark Rutland recently, and he pointed out that a
sequence of dlclose/dlopen mapping new code at the same addresses in
multithreaded environments is an issue on ARM, and possibly on Intel/AMD
with the newer TLB broadcast maintenance.

I maintain the membarrier(2) system call, which provides a
MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE command for this
purpose. It's been there since Linux 4.16. It can be configured
out (CONFIG_MEMBARRIER=n), but it's enabled by default.

Calling this after dlclose() in glibc would prevent this issue.

Is it handled in some other way, or should we open a bugzilla
entry to track this ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com