x86: treat pkey-0 special
Subsystems (3)
PATCH v3 1/1 x86: treat pkey-0 special
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 x86_64.
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
--- arch/x86/include/asm/pkeys.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
arch/x86/include/asm/pkeys.h +3 -2
@@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)* from pkey_alloc(). pkey 0 is special, and never * returned from pkey_alloc(). */ -if (pkey <=0 ) +if (pkey <0 )return false;if (pkey >=arch_max_pkey ())return false;
@@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm)static inline int mm_pkey_free (struct mm_struct *mm,int pkey) { -if (!mm_pkey_is_allocated (mm, pkey)) +/* pkey 0 is special and can never be freed */ +if (!pkey || !mm_pkey_is_allocated (mm, pkey))return -EINVAL ;mm_set_pkey_free (mm, pkey);
Signature · 1 line
1.8.3.1
Quoted 7 lines · Ram Pai
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
grep 'This patch' Documentation/process
Quoted 8 lines
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
x86_64.
I'm curious how the corresponding implementation on powerpc can be tested on x86_64. Copy and paste is not enough ...
Quoted 6 lines
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
Please put the history below the --- seperator. It's not part of the changelog. That way the tools can discard it when picking up the patch.
Quoted 23 lines
cc Dave Hansen <[email protected]>cc Michael Ellermen <[email protected]>cc Ingo Molnar <[email protected]>Signed-off-by Ram Pai <[email protected]>--- arch/x86/include/asm/pkeys.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)arch/x86/include/asm/pkeys.h +1
-1@@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)* from pkey_alloc(). pkey 0 is special, and never * returned from pkey_alloc(). */ -if (pkey <=0 ) +if (pkey <0 )return false;if (pkey >=arch_max_pkey ())return false;
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 95
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arch/x86/include/asm/pkeys.h +1
-1@@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm)static inline int mm_pkey_free (struct mm_struct *mm,int pkey) { -if (!mm_pkey_is_allocated (mm, pkey)) +/* pkey 0 is special and can never be freed */
This comment is pretty useless. How should anyone figure out whats special about pkey 0?
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))
Why this extra check? mm_pkey_is_allocated(mm, 0) should not return true ever. If it does, then this wants to be fixed.
Thanks,
tglx
Quoted 3 lines · Thomas Gleixner
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))Why this extra check?
mm_pkey_is_allocated(mm, 0)should not return true ever. If it does, then this wants to be fixed.
I was thinking that we _do_ actually want it to seem allocated. It just get "allocated" implicitly when an mm is created. I think that will simplify the code if we avoid treating it specially in as many places as possible.
Quoted 9 lines · Dave Hansen
Quoted 3 lines · Thomas Gleixner
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))Why this extra check?
mm_pkey_is_allocated(mm, 0)should not return true ever. If it does, then this wants to be fixed.I was thinking that we _do_ actually want it to seem allocated. It just get "allocated" implicitly when an mm is created. I think that will simplify the code if we avoid treating it specially in as many places as possible.
That works as well.
Quoted 9 lines · Dave Hansen
Quoted 3 lines · Thomas Gleixner
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))Why this extra check?
mm_pkey_is_allocated(mm, 0)should not return true ever. If it does, then this wants to be fixed.I was thinking that we _do_ actually want it to seem allocated. It just get "allocated" implicitly when an mm is created. I think that will simplify the code if we avoid treating it specially in as many places as possible.
I think, the logic that makes pkey-0 special must to go
in arch-neutral code. How about checking for pkey-0 in sys_pkey_free()
itself?
RP
Quoted 5 lines · Ram Pai
Quoted 4 lines · Dave Hansen
Quoted 3 lines · Thomas Gleixner
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))Why this extra check?
mm_pkey_is_allocated(mm, 0)should not return true ever. If it does, then this wants to be fixed.
Quoted 7 lines
Quoted 4 lines
I was thinking that we _do_ actually want it to seem allocated. It just get "allocated" implicitly when an mm is created. I think that will simplify the code if we avoid treating it specially in as many places as possible.
I think, the logic that makes pkey-0 special must to go
in arch-neutral code. How about checking for pkey-0 insys_pkey_free()
itself?
This is for protection against shooting yourself in the foot? Yes, that can go in sys_pkey_free().
Does this need manpage and/or selftests updates?
Quoted 10 lines · Dave Hansen
Quoted 9 lines · Ram Pai
Quoted 8 lines · Dave Hansen
Quoted 3 lines · Thomas Gleixner
arch/x86/include/asm/pkeys.h int mm_pkey_alloc(struct mm_struct *mm) · line 96
Quoted 1 line
arch/x86/include/asm/pkeys.h +1
-0+if (!pkey || !mm_pkey_is_allocated (mm, pkey))Why this extra check?
mm_pkey_is_allocated(mm, 0)should not return true ever. If it does, then this wants to be fixed.I was thinking that we _do_ actually want it to seem allocated. It just get "allocated" implicitly when an mm is created. I think that will simplify the code if we avoid treating it specially in as many places as possible.
Quoted 8 lines
Quoted 3 lines
I think, the logic that makes pkey-0 special must to go
in arch-neutral code. How about checking for pkey-0 insys_pkey_free()
itself?This is for protection against shooting yourself in the foot? Yes, that can go in
sys_pkey_free().Does this need manpage and/or selftests updates?
Yes. it needs selftest, manpage and documentation updates too.
Unfortunately I am not getting enough reviewed-by for my selftests and documentation changes. :-( Need help!
Signature · 1 line
Ram Pai