Hi all,

On Fri, Oct 19, 2018 at 12:24:04PM +0100, Will Deacon wrote:

On Fri, Oct 19, 2018 at 12:15:43PM +0100, Catalin Marinas wrote:

quoted

On Fri, Oct 05, 2018 at 09:47:44AM +0100, Kristina Martsenko wrote:

quoted

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
new file mode 100644
index 000000000000..2aefedc31d9e
--- /dev/null
+++ b/arch/arm64/include/asm/pointer_auth.h

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef __ASM_POINTER_AUTH_H
+#define __ASM_POINTER_AUTH_H
+
+#include <linux/random.h>
+
+#include <asm/cpufeature.h>
+#include <asm/sysreg.h>
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+/*
+ * Each key is a 128-bit quantity which is split across a pair of 64-bit
+ * registers (Lo and Hi).
+ */
+struct ptrauth_key {
+	unsigned long lo, hi;
+};
+
+/*
+ * We give each process its own instruction A key (APIAKey), which is shared by
+ * all threads. This is inherited upon fork(), and reinitialised upon exec*().
+ * All other keys are currently unused, with APIBKey, APDAKey, and APBAKey
+ * instructions behaving as NOPs.
+ */

I don't remember the past discussions but I assume the tools guys are ok
with a single key shared by multiple threads. Ramana, could you ack this
part, FTR?

(and it would help if someone from the Android and Chrome camps can
confirm)

FWIW: I think we should be entertaining a prctl() interface to use a new
key on a per-thread basis. Obviously, this would need to be used with care
(e.g. you'd fork(); use the prctl() and then you'd better not return from
the calling function!).

Assuming we want this (Kees -- I was under the impression that everything in
Android would end up with the same key otherwise?), then the question is
do we want:

  - prctl() get/set operations for the key, or
  - prctl() set_random_key operation, or
  - both of the above?

Part of the answer to that may lie in the requirements of CRIU, where I
strongly suspect they need explicit get/set operations, although these
could be gated on CONFIG_CHECKPOINT_RESTORE=y.

I managed to speak to the CRIU developers at LPC. The good news is that
their preference is for a ptrace()-based interface for getting and setting
the keys, so the only prctl() operation we need is to set a random key
(separately for A and B).

Will