[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <81f06e13-0e05-4421-9a65-9fa65ef5ebae@linaro.org>
Date: Fri, 10 Jan 2025 14:24:17 -0300
From: Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Florian Weimer <fweimer@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
"carlos@...hat.com" <carlos@...hat.com>, Mark Rutland
<mark.rutland@....com>, linux-kernel <linux-kernel@...r.kernel.org>,
x86@...nel.org, paulmck <paulmck@...nel.org>,
Michael Jeanson <mjeanson@...icios.com>
Subject: Re: Prevent inconsistent CPU state after sequence of dlclose/dlopen
On 10/01/25 14:15, Mathieu Desnoyers wrote:
> On 2025-01-10 12:10, Florian Weimer wrote:
>> * Mathieu Desnoyers:
>>
>>> On 2025-01-10 11:54, Peter Zijlstra wrote:
>>>> On Fri, Jan 10, 2025 at 10:55:36AM -0500, Mathieu Desnoyers wrote:
>>>>> 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.
>>>> What is the exact race? Should not munmap() invalidate the TLBs
>>>> before
>>>> it allows overlapping mmap() to complete?
>>>
>>> The race Mark mentioned (on ARM) is AFAIU the following scenario:
>>>
>>> CPU 0 CPU 1
>>>
>>> - dlopen()
>>> - mmap PROT_EXEC @addr
>>> - fetch insn @addr, CPU state expects unchanged insn.
>>> - execute unrelated code
>>> - dlclose(addr)
>>> - munmap @addr
>>> - dlopen()
>>> - mmap PROT_EXEC @addr
>>> - fetch new insn @addr. Incoherent CPU state.
>>
>> Unmapping an object while code is executing in it is undefined.
>
> That's not the scenario though. In this scenario, CPU 1 executes
> _unrelated code_ while we unmap @addr.
But in this scenario you still a concurrent dlclose while you have a running
thread executing code from that module, right? Or am I still missing something
here?
Or, are you saying that even after dlopen returns (assuming the scenario where
it maps the code in a previous used mapping), the CPU is in an inconsistent
state unless MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE is issued?
Powered by blists - more mailing lists