[to-be-updated] fs-proc-expose-rseq-configuration.patch removed from -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: fs/proc: expose RSEQ configuration
has been removed from the -mm tree.  Its filename was
     fs-proc-expose-rseq-configuration.patch

This patch was dropped because an updated version will be merged

------------------------------------------------------
From: Piotr Figiel <figiel@google.com>
Subject: fs/proc: expose RSEQ configuration

For userspace checkpoint and restore (C/R) some 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.

Link: https://lkml.kernel.org/r/20210113174127.2500051-1-figiel@google.com
Signed-off-by: Piotr Figiel <figiel@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexey Gladkov <gladkov.alexey@gmail.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Oskolkov <posk@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: Paul Turner <pjt@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/base.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/fs/proc/base.c~fs-proc-expose-rseq-configuration
+++ a/fs/proc/base.c
@@ -659,6 +659,20 @@ static int proc_pid_syscall(struct seq_f
 
 	return 0;
 }
+
+#ifdef CONFIG_RSEQ
+static int proc_pid_rseq(struct seq_file *m, struct pid_namespace *ns,
+				struct pid *pid, struct task_struct *task)
+{
+	int res = lock_trace(task);
+
+	if (res)
+		return res;
+	seq_printf(m, "0x%llx 0x%x\n", (uint64_t)task->rseq, task->rseq_sig);
+	unlock_trace(task);
+	return 0;
+}
+#endif /* CONFIG_RSEQ */
 #endif /* CONFIG_HAVE_ARCH_TRACEHOOK */
 
 /************************************************************************/
@@ -3179,6 +3193,9 @@ static const struct pid_entry tgid_base_
 	REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",    S_IRUSR, proc_pid_syscall),
+#ifdef CONFIG_RSEQ
+	ONE("rseq",       S_IRUSR, proc_pid_rseq),
+#endif
 #endif
 	REG("cmdline",    S_IRUGO, proc_pid_cmdline_ops),
 	ONE("stat",       S_IRUGO, proc_tgid_stat),
@@ -3519,6 +3536,9 @@ static const struct pid_entry tid_base_s
 			 &proc_pid_set_comm_operations, {}),
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",   S_IRUSR, proc_pid_syscall),
+#ifdef CONFIG_RSEQ
+	ONE("rseq",      S_IRUSR, proc_pid_rseq),
+#endif
 #endif
 	REG("cmdline",   S_IRUGO, proc_pid_cmdline_ops),
 	ONE("stat",      S_IRUGO, proc_tid_stat),
_

Patches currently in -mm which might be from figiel@google.com are