Re: [PATCH] powerpc, pkey: make protection key 0 less special
From: Ram Pai <hidden>
Date: 2018-03-27 01:04:10
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On Mon, Mar 26, 2018 at 04:31:41PM -0700, Ram Pai wrote:
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. Lets make pkey-0 less special and treat it almost like any other key. Thus it can be explicitly associated with any address range, and can be freed. This gives the application more flexibility and power. The ability to free pkey-0 must be used responsibily, since pkey-0 is associated with almost all address-range by default. Even with this change pkey-0 continues to be slightly more special from the following point of view. (a) it is implicitly allocated. (b) it is the default key assigned to any address-range. Tested on powerpc.
This patch is not entirely correct.
quoted hunk ↗ jump to hunk
cc: Thomas Gleixner <redacted> cc: Dave Hansen <redacted> cc: Michael Ellermen <mpe@ellerman.id.au> cc: Ingo Molnar <mingo@kernel.org> cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ram Pai <redacted> --- arch/powerpc/include/asm/pkeys.h | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-)diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h index 0409c80..9c7d3bd 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;
This is wrong. pkey-0 should not be treated any special here. Will fix this and send a new patch. Sorry for the noise. RP