linux-kernel - Re: [RESEND RFC PATCH 0/3] Provide fast access to thread specific data

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6A88B271-EC5E-46B7-8D60-A7543635FDC5@oracle.com>
Date:   Mon, 13 Sep 2021 17:36:24 +0000
From:   Prakash Sangappa <prakash.sangappa@...cle.com>
To:     Peter Oskolkov <posk@...gle.com>
CC:     Jann Horn <jannh@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Paul Turner <pjt@...gle.com>,
        Peter Oskolkov <posk@...k.io>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RESEND RFC PATCH 0/3] Provide fast access to thread specific
 data



> On Sep 10, 2021, at 12:36 PM, Peter Oskolkov <posk@...gle.com> wrote:
> 
> On Fri, Sep 10, 2021 at 12:12 PM Jann Horn <jannh@...gle.com> wrote:
>> 
>> On Fri, Sep 10, 2021 at 6:28 PM Peter Oskolkov <posk@...gle.com> wrote:
>>> On Fri, Sep 10, 2021 at 9:13 AM Prakash Sangappa
>>> <prakash.sangappa@...cle.com> wrote:
>>>>> Do you think your sys_task_getshared can be tweaked to return an
>>>>> arbitrarily-sized block of memory (subject to overall constraints)
>>>>> rather than a fixed number of "options"?
>>>> 
>>>> I suppose it could. How big of a size? We don’t want to hold on to
>>>> arbitrarily large  amount of pinned memory. The preference would
>>>> be for the kernel to decide what is going to be shared based on
>>>> what functionality/data sharing is supported. In that sense the size
>>>> is pre defined not something the userspace/application can ask.
>>> 
>>> There could be a sysctl or some other mechanism that limits the amount
>>> of memory pinned per mm (or per task). Having "options" hardcoded for
>>> such a generally useful feature seems limiting...
>> 
>> That seems like it'll just create trouble a few years down the line
>> when the arbitrarily-chosen limit that nobody is monitoring blows up
>> in someone's production environment.
>> 
>> If this area is used for specific per-thread items, then the kernel
>> should be able to enforce that you only allocate as much space as is
>> needed for all threads of the process (based on the maximum number
>> that have ever been running in parallel in the process), right? Which
>> would probably work best if the kernel managed those allocations.
> 
> This sounds, again, as if the kernel should be aware of the kind of
> items being allocated; having a more generic mechanism of allocating
> pinned memory for the userspace to use at its discretion would be more
> generally useful, I think. But how then the kernel/system should be
> protected from a buggy or malicious process trying to grab too much?
> 
> One option would be to have a generic in-kernel mechanism for this,
> but expose it to the userspace via domain-specific syscalls that do
> the accounting you hint at. This sounds a bit like an over-engineered
> solution, though…


What will this pinned memory be used for in your use case,
can you explain?