linux-kernel - Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ

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Date:   Thu, 11 Mar 2021 17:51:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Piotr Figiel <figiel@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        paulmck <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Florian Weimer <fweimer@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Oskolkov <posk@...gle.com>,
        Kamil Yurtsever <kyurtsever@...gle.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Paul Turner <pjt@...gle.com>, emmir <emmir@...gle.com>,
        linux-man <linux-man@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request

On Thu, Mar 11, 2021 at 09:51:56AM -0500, Mathieu Desnoyers wrote:
> 
> 
> ----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@...gle.com wrote:
> 
> > For userspace checkpoint and restore (C/R) a way of getting process state
> > containing RSEQ configuration is needed.
> > 
> > There are two ways this information is going to be used:
> > - to re-enable RSEQ for threads which had it enabled before C/R
> > - to detect if a thread was in a critical section during C/R
> > 
> > Since C/R preserves TLS memory and addresses RSEQ ABI will be restored
> > using the address registered before C/R.
> > 
> > Detection whether the thread is in a critical section during C/R is needed
> > to enforce behavior of RSEQ abort during C/R. Attaching with ptrace()
> > before registers are dumped itself doesn't cause RSEQ abort.
> > Restoring the instruction pointer within the critical section is
> > problematic because rseq_cs may get cleared before the control is passed
> > to the migrated application code leading to RSEQ invariants not being
> > preserved. C/R code will use RSEQ ABI address to find the abort handler
> > to which the instruction pointer needs to be set.
> > 
> > To achieve above goals expose the RSEQ ABI address and the signature value
> > with the new ptrace request PTRACE_GET_RSEQ_CONFIGURATION.
> > 
> > This new ptrace request can also be used by debuggers so they are aware
> > of stops within restartable sequences in progress.
> > 
> > Signed-off-by: Piotr Figiel <figiel@...gle.com>
> > Reviewed-by: Michal Miroslaw <emmir@...gle.com>
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

How do we route this? Do I stick this in tip/sched/core as being an rseq
patch?