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Subject[PATCH 1/9] x86, pkeys: do not special case protection key 0
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From: Dave Hansen <dave.hansen@linux.intel.com>

mm_pkey_is_allocated() treats pkey 0 as unallocated. That is
inconsistent with the manpages, and also inconsistent with
mm->context.pkey_allocation_map. Stop special casing it and only
disallow values that are actually bad (< 0).

The end-user visible effect of this is that you can now use
mprotect_pkey() to set pkey=0.

This is a bit nicer than what Ram proposed because it is simpler
and removes special-casing for pkey 0. On the other hand, it does
allow applciations to pkey_free() pkey-0, but that's just a silly
thing to do, so we are not going to protect against it.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michael Ellermen <mpe@ellerman.id.au>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>p
Cc: Shuah Khan <shuah@kernel.org>
---

b/arch/x86/include/asm/mmu_context.h | 2 +-
b/arch/x86/include/asm/pkeys.h | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)

diff -puN arch/x86/include/asm/mmu_context.h~x86-pkey-0-default-allocated arch/x86/include/asm/mmu_context.h
--- a/arch/x86/include/asm/mmu_context.h~x86-pkey-0-default-allocated 2018-03-21 15:47:48.182198927 -0700
+++ b/arch/x86/include/asm/mmu_context.h 2018-03-21 15:47:48.187198927 -0700
@@ -192,7 +192,7 @@ static inline int init_new_context(struc

#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
- /* pkey 0 is the default and always allocated */
+ /* pkey 0 is the default and allocated implicitly */
mm->context.pkey_allocation_map = 0x1;
/* -1 means unallocated or invalid */
mm->context.execute_only_pkey = -1;
diff -puN arch/x86/include/asm/pkeys.h~x86-pkey-0-default-allocated arch/x86/include/asm/pkeys.h
--- a/arch/x86/include/asm/pkeys.h~x86-pkey-0-default-allocated 2018-03-21 15:47:48.184198927 -0700
+++ b/arch/x86/include/asm/pkeys.h 2018-03-21 15:47:48.188198927 -0700
@@ -49,10 +49,10 @@ bool mm_pkey_is_allocated(struct mm_stru
{
/*
* "Allocated" pkeys are those that have been returned
- * from pkey_alloc(). pkey 0 is special, and never
- * returned from pkey_alloc().
+ * from pkey_alloc() or pkey 0 which is allocated
+ * implicitly when the mm is created.
*/
- if (pkey <= 0)
+ if (pkey < 0)
return false;
if (pkey >= arch_max_pkey())
return false;
_
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