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==== Dump ====
==== Dump ====
We need to determine where the <code>struct rseq</code> is and dump its address length and signature.
To achieve that we use special ptrace handle <code>PTRACE_GET_RSEQ_CONFIGURATION</code> (refer to the <code>dump_thread_rseq</code> function).
We have to fix up IP to the abort handler.
==== Restore ====
==== Restore ====
We need to take data about the <code>struct rseq</code> from the image (see images/rseq.proto) and register it from the parasite context using the <code>rseq</code> syscall (take a look on <code>restore_rseq</code> in criu/pie/restorer.c)
No additional actions here. The process will be restored and will continue execution from the abort handler (not within the rseq CS!).
=== inside CS: <code>flags</code> is <code>RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL</code> ===
=== inside CS: <code>flags</code> is <code>RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL</code> ===
Rare case, but we support it too.
Rare case, but we support it too. If the rseq CS has <code>RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL</code> flag it means that its technically
non-abortable. So, from the first glance, it seems like we can just not do anything special: save rseq structure address, not fix up IP.
This is incorrect.
The kernel will clean up <code>(struct rseq).rseq_cs</code> pointer once we jump into the parasite on the dump:
<pre>
static int rseq_ip_fixup(struct pt_regs *regs)
{
...
/*
* Handle potentially not being within a critical section.
* If not nested over a rseq critical section, restart is useless.
* Clear the rseq_cs pointer and return.
*/
if (!in_rseq_cs(ip, &rseq_cs))
return clear_rseq_cs(t);
</pre>
and after the restore process will continue the rseq CS execution from the same place (it's okay) but from the kernel point of view,
the process will continue this execution as not being within the rseq CS (that's bad!). Because the kernel determines execution context from the <code>(struct rseq).rseq_cs</code> field.
==== Dump ====
==== Dump ====
We need to determine where the <code>struct rseq</code> is and dump its address length and signature.
To achieve that we use special ptrace handle <code>PTRACE_GET_RSEQ_CONFIGURATION</code> (refer to the <code>dump_thread_rseq</code> function).
We save IP as it was (not doing fixup), but we have to save <code>(struct rseq).rseq_cs</code> field into the CRIU image.
==== Restore ====
==== Restore ====
We need to take data about the <code>struct rseq</code> from the image (see images/rseq.proto) and register it from the parasite context using the <code>rseq</code> syscall (take a look on <code>restore_rseq</code> in criu/pie/restorer.c)
We need to restore <code>(struct rseq).rseq_cs</code> memory externaly using ptrace <code>POKEAREA</code> (see <code>restore_rseq_cs</code>).
== TODO ==
== TODO ==