powerpc/pkeys: key allocation/deallocation must not change pkey registers

Key allocation and deallocation has the side effect of programming the
UAMOR/AMR/IAMR registers. This is wrong, since its the responsibility of
the application and not that of the kernel, to modify the permission on
the key.

Do not modify the pkey registers at key allocation/deallocation.

This patch also fixes a bug where a sys_pkey_free() resets the UAMOR
bits of the key, thus making its permissions unmodifiable from user
space. Later if the same key gets reallocated from a different thread
this thread will no longer be able to change the permissions on the key.

Fixes: cf43d3b2 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/pkeys.h

@@ -94,8 +94,6 @@ static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 		__mm_pkey_is_allocated(mm, pkey));
 }
 
-extern void __arch_activate_pkey(int pkey);
-extern void __arch_deactivate_pkey(int pkey);
 /*
  * Returns a positive, 5-bit key on success, or -1 on failure.
  * Relies on the mmap_sem to protect against concurrency in mm_pkey_alloc() and
@@ -124,11 +122,6 @@ static inline int mm_pkey_alloc(struct mm_struct *mm)
 	ret = ffz((u32)mm_pkey_allocation_map(mm));
 	__mm_pkey_allocated(mm, ret);
 
-	/*
-	 * Enable the key in the hardware
-	 */
-	if (ret > 0)
-		__arch_activate_pkey(ret);
 	return ret;
 }
 
@@ -140,10 +133,6 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
 	if (!mm_pkey_is_allocated(mm, pkey))
 		return -EINVAL;
 
-	/*
-	 * Disable the key in the hardware
-	 */
-	__arch_deactivate_pkey(pkey);
 	__mm_pkey_free(mm, pkey);
 
 	return 0;

arch/powerpc/mm/pkeys.c

@@ -218,33 +218,6 @@ static inline void init_iamr(int pkey, u8 init_bits)
 	write_iamr(old_iamr | new_iamr_bits);
 }
 
-static void pkey_status_change(int pkey, bool enable)
-{
-	u64 old_uamor;
-
-	/* Reset the AMR and IAMR bits for this key */
-	init_amr(pkey, 0x0);
-	init_iamr(pkey, 0x0);
-
-	/* Enable/disable key */
-	old_uamor = read_uamor();
-	if (enable)
-		old_uamor |= (0x3ul << pkeyshift(pkey));
-	else
-		old_uamor &= ~(0x3ul << pkeyshift(pkey));
-	write_uamor(old_uamor);
-}
-
-void __arch_activate_pkey(int pkey)
-{
-	pkey_status_change(pkey, true);
-}
-
-void __arch_deactivate_pkey(int pkey)
-{
-	pkey_status_change(pkey, false);
-}
-
 /*
  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
  * specified in @init_val.