Applications need the ability to associate an address-range with some
key and latter revert to its initial default key. Pkey-0 comes close to
providing this function but falls short, because the current
implementation disallows applications to explicitly associate pkey-0 to
the address range.
This patch clarifies the semantics of pkey-0 and provides the
corresponding implementation on powerpc.
Pkey-0 is special with the following semantics.
(a) it is implicitly allocated and can never be freed. It always exists.
(b) it is the default key assigned to any address-range.
(c) it can be explicitly associated with any address-range.
Tested on powerpc.
History:
v3 : added clarification of the semantics of pkey0.
-- suggested by Dave Hansen
v2 : split the patch into two, one for x86 and one for powerpc
-- suggested by Michael Ellermen
cc: Dave Hansen <dave.hansen@xxxxxxxxx>
cc: Michael Ellermen <mpe@xxxxxxxxxxxxxx>
cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
---
arch/powerpc/include/asm/pkeys.h | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 0409c80..3c1deec 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -101,10 +101,18 @@ static inline u16 pte_to_pkey_bits(u64 pteflags)
static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
{
- /* A reserved key is never considered as 'explicitly allocated' */
- return ((pkey < arch_max_pkey()) &&
- !__mm_pkey_is_reserved(pkey) &&
- __mm_pkey_is_allocated(mm, pkey));
+ /* pkey 0 is allocated by default. */
+ if (!pkey)
+ return true;
+
+ if (pkey < 0 || pkey >= arch_max_pkey())
+ return false;
+
+ /* Reserved keys are never allocated. */
+ if (__mm_pkey_is_reserved(pkey))
+ return false;
+
+ return __mm_pkey_is_allocated(mm, pkey);
}
extern void __arch_activate_pkey(int pkey);
@@ -150,7 +158,8 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
if (static_branch_likely(&pkey_disabled))
return -1;
- if (!mm_pkey_is_allocated(mm, pkey))
+ /* pkey 0 cannot be freed */
+ if (!pkey || !mm_pkey_is_allocated(mm, pkey))
return -EINVAL;
/*
--
1.8.3.1
