Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request

[Peter Zijlstra]

On Thu, Mar 11, 2021 at 09:51:56AM -0500, Mathieu Desnoyers wrote:
> 
> 
> ----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@xxxxxxxxxx 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@xxxxxxxxxx>
> > Reviewed-by: Michal Miroslaw <emmir@xxxxxxxxxx>
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

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