powerpc: implementation for arch_set_user_pkey_access()

This patch provides the detailed implementation for
a user to allocate a key and enable it in the hardware.

It provides the plumbing, but it cannot be used till
the system call is implemented. The next patch  will
do so.

Reviewed-by: Thiago Jung Bauermann <bauerman@linux.vnet.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

@@ -128,10 +128,14 @@ static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
 	return 0;
 }
 
+extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
+				       unsigned long init_val);
 static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 					    unsigned long init_val)
 {
-	return 0;
+	if (static_branch_likely(&pkey_disabled))
+		return -EINVAL;
+	return __arch_set_user_pkey_access(tsk, pkey, init_val);
 }
 
 extern void pkey_mm_init(struct mm_struct *mm);

arch/powerpc/mm/pkeys.c

@@ -5,6 +5,7 @@
  * Copyright 2017, Ram Pai, IBM Corporation.
  */
 
+#include <asm/mman.h>
 #include <linux/pkeys.h>
 
 DEFINE_STATIC_KEY_TRUE(pkey_disabled);
@@ -13,6 +14,9 @@ int  pkeys_total;		/* Total pkeys as per device tree */
 u32  initial_allocation_mask;	/* Bits set for reserved keys */
 
 #define AMR_BITS_PER_PKEY 2
+#define AMR_RD_BIT 0x1UL
+#define AMR_WR_BIT 0x2UL
+#define IAMR_EX_BIT 0x1UL
 #define PKEY_REG_BITS (sizeof(u64)*8)
 #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
 
@@ -108,6 +112,20 @@ static inline void write_uamor(u64 value)
 	mtspr(SPRN_UAMOR, value);
 }
 
+static bool is_pkey_enabled(int pkey)
+{
+	u64 uamor = read_uamor();
+	u64 pkey_bits = 0x3ul << pkeyshift(pkey);
+	u64 uamor_pkey_bits = (uamor & pkey_bits);
+
+	/*
+	 * Both the bits in UAMOR corresponding to the key should be set or
+	 * reset.
+	 */
+	WARN_ON(uamor_pkey_bits && (uamor_pkey_bits != pkey_bits));
+	return !!(uamor_pkey_bits);
+}
+
 static inline void init_amr(int pkey, u8 init_bits)
 {
 	u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
@@ -150,3 +168,25 @@ 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.
+ */
+int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
+				unsigned long init_val)
+{
+	u64 new_amr_bits = 0x0ul;
+
+	if (!is_pkey_enabled(pkey))
+		return -EINVAL;
+
+	/* Set the bits we need in AMR: */
+	if (init_val & PKEY_DISABLE_ACCESS)
+		new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
+	else if (init_val & PKEY_DISABLE_WRITE)
+		new_amr_bits |= AMR_WR_BIT;
+
+	init_amr(pkey, new_amr_bits);
+	return 0;
+}