[PATCH] powerpc64: Add architecture-specific memory protection key support [BZ #23202]

[Florian Weimer]

The 32-bit protection key behavior is somewhat unclear on 32-bit powerpc,
so this change is restricted to the 64-bit variants.

Flag translation is needed because of hardware differences between the
POWER implementation (read and write flags) and the Intel implementation
(write and read+write flags).

Tested on powerpc64-linux-gnu, on a system that supports memory
protection keys, along with Lucas' test change.

-----
 .../unix/sysv/linux/powerpc/powerpc64/arch-pkey.h  | 55 ++++++++++++++++++++++
 .../unix/sysv/linux/powerpc/powerpc64/pkey_get.c   | 42 +++++++++++++++++
 .../unix/sysv/linux/powerpc/powerpc64/pkey_set.c   | 48 +++++++++++++++++++
 3 files changed, 145 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/arch-pkey.h b/sysdeps/unix/sysv/linux/powerpc/powerpc64/arch-pkey.h
new file mode 100644
index 0000000000..623b073d5a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/arch-pkey.h
@@ -0,0 +1,55 @@
+/* Helper functions for manipulating memory protection keys, for powerpc64.
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _ARCH_PKEY_H
+#define _ARCH_PKEY_H
+
+/* Read and write access bits in the AMR register.  Needs to be
+   translated from and to PKEY_DISABLE_* flags.  */
+#define PKEY_AMR_READ 1UL
+#define PKEY_AMR_WRITE 2UL
+
+/* Return the value of the AMR register.  */
+static inline unsigned long int
+pkey_read (void)
+{
+  unsigned long int result;
+  __asm__ volatile ("mfspr %0, 13" : "=r" (result));
+  return result;
+}
+
+/* Overwrite the AMR register with VALUE.  */
+static inline void
+pkey_write (unsigned long int value)
+{
+  __asm__ volatile ("mtspr 13, %0" : : "r" (value));
+}
+
+/* Number of the largest supported key.  This depends on the width of
+   the AMR register.  */
+#define PKEY_MAX (sizeof (unsigned long int) * 8 / 2 - 1)
+_Static_assert (PKEY_MAX == 15 || PKEY_MAX == 31, "PKEY_MAX value");
+
+/* Translate key number into AMR index position.  */
+static inline int
+pkey_index (int key)
+{
+  return 2 * (PKEY_MAX - key);
+}
+
+#endif /* _ARCH_PKEY_H */
diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_get.c b/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_get.c
new file mode 100644
index 0000000000..856ba061b9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_get.c
@@ -0,0 +1,42 @@
+/* Reading the per-thread memory protection key, powerpc64 version.
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <arch-pkey.h>
+#include <errno.h>
+#include <sys/mman.h>
+
+int
+pkey_get (int key)
+{
+  if (key < 0 || key > PKEY_MAX)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+  unsigned int index = pkey_index (key);
+  unsigned long int amr = pkey_read ();
+  unsigned int bits = (amr >> index) & 3;
+
+  /* Translate from AMR values.  PKEY_AMR_READ standing alone is not
+     currently representable.  */
+  if (bits & PKEY_AMR_READ)
+    return PKEY_DISABLE_ACCESS;
+  else if (bits == PKEY_AMR_WRITE)
+    return PKEY_DISABLE_WRITE;
+  return 0;
+}
diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_set.c b/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_set.c
new file mode 100644
index 0000000000..20b372ee29
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/pkey_set.c
@@ -0,0 +1,48 @@
+/* Changing the per-thread memory protection key, powerpc64 version.
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <arch-pkey.h>
+#include <errno.h>
+#include <sys/mman.h>
+
+int
+pkey_set (int key, unsigned int rights)
+{
+  if (key < 0 || key > PKEY_MAX || rights > 3)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  /* Translate to AMR bit values.  */
+  unsigned long int bits;
+  if (rights & PKEY_DISABLE_ACCESS)
+    /* The PKEY_DISABLE_WRITE bit does not matter.  */
+    bits = PKEY_AMR_READ | PKEY_AMR_WRITE;
+  else if (rights == PKEY_DISABLE_WRITE)
+    bits = PKEY_AMR_WRITE;
+  else
+    bits = 0;
+
+  unsigned int index = pkey_index (key);
+  unsigned long int mask = 3UL << index;
+  unsigned long int amr = pkey_read ();
+  amr = (amr & ~mask) | (bits << index);
+  pkey_write (amr);
+  return 0;
+}