Re: [PATCH] Implement protection key support for POWER

[Carlos O'Donell <carlos at redhat dot com>]

On 05/23/2018 11:14 AM, Florian Weimer wrote:
> This still does not address the misc/tst-pkeys failure because there
> are kernel bugs.
> 
> I'm not entirely sure if the 32-bit AMR mapping is correct because
> the kernel allocates keys starting with the MSB position.  If in
> doubt, we could make this specific to powerpc64.
It's nice to see support for this going in early, and I particularly like
the direction this is going with respect to signal handler support you
are discussing upstream in linux. Involving userspace developers will yield
semantics that make more sense for library and application developers rather
than singular use cases driving the hardware e.g. just the needs of a database.

Is this more of an RFC than PATCH?

Regarding this specific patch, what happens when you are not on an ISA3.0
hardware that supports AMR/IAMR/UAMOR registers?

Does tst-pkeys test everything that is required to be tested here?

> Subject: [PATCH] powerpc: Implement memory protection key support
> To: libc-alpha@sourceware.org
> 
> This commit adds the architecture-specific implementations for
> pkey_set and pkey_get.
> 
> Execute-only keys are not yet supported.
> 
> 2018-05-23  Florian Weimer  <fweimer@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/powerpc/arch-pkey.h: New file.
> 	* sysdeps/unix/sysv/linux/powerpc/pkey_set.c: Likewise.
> 	* sysdeps/unix/sysv/linux/powerpc/pkey_get.c: Likewise.
> 
> diff --git a/sysdeps/unix/sysv/linux/powerpc/arch-pkey.h b/sysdeps/unix/sysv/linux/powerpc/arch-pkey.h
> new file mode 100644
> index 0000000000..9431826a68
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/arch-pkey.h
> @@ -0,0 +1,55 @@
> +/* Helper functions for manipulating memory protection keys.
> +   Copyright (C) 2017-2018 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/pkey_get.c b/sysdeps/unix/sysv/linux/powerpc/pkey_get.c
> new file mode 100644
> index 0000000000..9c315a4766
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/pkey_get.c
> @@ -0,0 +1,42 @@
> +/* Reading the per-thread memory protection key, x86_64 version.
> +   Copyright (C) 2017-2018 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/pkey_set.c b/sysdeps/unix/sysv/linux/powerpc/pkey_set.c
> new file mode 100644
> index 0000000000..f57a46f1ed
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/pkey_set.c
> @@ -0,0 +1,48 @@
> +/* Changing the per-thread memory protection key, powerpc64 version.
> +   Copyright (C) 2017-2018 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;
> +}


-- 
Cheers,
Carlos.