xref: /linux/arch/powerpc/mm/book3s64/pkeys.c (revision 547f574fd9d5e3925d47fd44decbf6ab6df94b0e)
1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * PowerPC Memory Protection Keys management
4  *
5  * Copyright 2017, Ram Pai, IBM Corporation.
6  */
7 
8 #include <asm/mman.h>
9 #include <asm/mmu_context.h>
10 #include <asm/mmu.h>
11 #include <asm/setup.h>
12 #include <linux/pkeys.h>
13 #include <linux/of_fdt.h>
14 
15 int  num_pkey;		/* Max number of pkeys supported */
16 /*
17  *  Keys marked in the reservation list cannot be allocated by  userspace
18  */
19 u32 reserved_allocation_mask __ro_after_init;
20 
21 /* Bits set for the initially allocated keys */
22 static u32 initial_allocation_mask __ro_after_init;
23 
24 /*
25  * Even if we allocate keys with sys_pkey_alloc(), we need to make sure
26  * other thread still find the access denied using the same keys.
27  */
28 static u64 default_amr = ~0x0UL;
29 static u64 default_iamr = 0x5555555555555555UL;
30 u64 default_uamor __ro_after_init;
31 /*
32  * Key used to implement PROT_EXEC mmap. Denies READ/WRITE
33  * We pick key 2 because 0 is special key and 1 is reserved as per ISA.
34  */
35 static int execute_only_key = 2;
36 static bool pkey_execute_disable_supported;
37 
38 
39 #define AMR_BITS_PER_PKEY 2
40 #define AMR_RD_BIT 0x1UL
41 #define AMR_WR_BIT 0x2UL
42 #define IAMR_EX_BIT 0x1UL
43 #define PKEY_REG_BITS (sizeof(u64) * 8)
44 #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
45 
46 static int __init dt_scan_storage_keys(unsigned long node,
47 				       const char *uname, int depth,
48 				       void *data)
49 {
50 	const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
51 	const __be32 *prop;
52 	int *pkeys_total = (int *) data;
53 
54 	/* We are scanning "cpu" nodes only */
55 	if (type == NULL || strcmp(type, "cpu") != 0)
56 		return 0;
57 
58 	prop = of_get_flat_dt_prop(node, "ibm,processor-storage-keys", NULL);
59 	if (!prop)
60 		return 0;
61 	*pkeys_total = be32_to_cpu(prop[0]);
62 	return 1;
63 }
64 
65 static int scan_pkey_feature(void)
66 {
67 	int ret;
68 	int pkeys_total = 0;
69 
70 	/*
71 	 * Pkey is not supported with Radix translation.
72 	 */
73 	if (early_radix_enabled())
74 		return 0;
75 
76 	ret = of_scan_flat_dt(dt_scan_storage_keys, &pkeys_total);
77 	if (ret == 0) {
78 		/*
79 		 * Let's assume 32 pkeys on P8/P9 bare metal, if its not defined by device
80 		 * tree. We make this exception since some version of skiboot forgot to
81 		 * expose this property on power8/9.
82 		 */
83 		if (!firmware_has_feature(FW_FEATURE_LPAR)) {
84 			unsigned long pvr = mfspr(SPRN_PVR);
85 
86 			if (PVR_VER(pvr) == PVR_POWER8 || PVR_VER(pvr) == PVR_POWER8E ||
87 			    PVR_VER(pvr) == PVR_POWER8NVL || PVR_VER(pvr) == PVR_POWER9)
88 				pkeys_total = 32;
89 		}
90 	}
91 
92 	/*
93 	 * Adjust the upper limit, based on the number of bits supported by
94 	 * arch-neutral code.
95 	 */
96 	pkeys_total = min_t(int, pkeys_total,
97 			    ((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) + 1));
98 	return pkeys_total;
99 }
100 
101 void __init pkey_early_init_devtree(void)
102 {
103 	int pkeys_total, i;
104 
105 	/*
106 	 * We define PKEY_DISABLE_EXECUTE in addition to the arch-neutral
107 	 * generic defines for PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
108 	 * Ensure that the bits a distinct.
109 	 */
110 	BUILD_BUG_ON(PKEY_DISABLE_EXECUTE &
111 		     (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
112 
113 	/*
114 	 * pkey_to_vmflag_bits() assumes that the pkey bits are contiguous
115 	 * in the vmaflag. Make sure that is really the case.
116 	 */
117 	BUILD_BUG_ON(__builtin_clzl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) +
118 		     __builtin_popcountl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)
119 				!= (sizeof(u64) * BITS_PER_BYTE));
120 
121 	/*
122 	 * Only P7 and above supports SPRN_AMR update with MSR[PR] = 1
123 	 */
124 	if (!early_cpu_has_feature(CPU_FTR_ARCH_206))
125 		return;
126 
127 	/* scan the device tree for pkey feature */
128 	pkeys_total = scan_pkey_feature();
129 	if (!pkeys_total)
130 		goto out;
131 
132 	/* Allow all keys to be modified by default */
133 	default_uamor = ~0x0UL;
134 
135 	cur_cpu_spec->mmu_features |= MMU_FTR_PKEY;
136 
137 	/*
138 	 * The device tree cannot be relied to indicate support for
139 	 * execute_disable support. Instead we use a PVR check.
140 	 */
141 	if (pvr_version_is(PVR_POWER7) || pvr_version_is(PVR_POWER7p))
142 		pkey_execute_disable_supported = false;
143 	else
144 		pkey_execute_disable_supported = true;
145 
146 #ifdef CONFIG_PPC_4K_PAGES
147 	/*
148 	 * The OS can manage only 8 pkeys due to its inability to represent them
149 	 * in the Linux 4K PTE. Mark all other keys reserved.
150 	 */
151 	num_pkey = min(8, pkeys_total);
152 #else
153 	num_pkey = pkeys_total;
154 #endif
155 
156 	if (unlikely(num_pkey <= execute_only_key) || !pkey_execute_disable_supported) {
157 		/*
158 		 * Insufficient number of keys to support
159 		 * execute only key. Mark it unavailable.
160 		 */
161 		execute_only_key = -1;
162 	} else {
163 		/*
164 		 * Mark the execute_only_pkey as not available for
165 		 * user allocation via pkey_alloc.
166 		 */
167 		reserved_allocation_mask |= (0x1 << execute_only_key);
168 
169 		/*
170 		 * Deny READ/WRITE for execute_only_key.
171 		 * Allow execute in IAMR.
172 		 */
173 		default_amr  |= (0x3ul << pkeyshift(execute_only_key));
174 		default_iamr &= ~(0x1ul << pkeyshift(execute_only_key));
175 
176 		/*
177 		 * Clear the uamor bits for this key.
178 		 */
179 		default_uamor &= ~(0x3ul << pkeyshift(execute_only_key));
180 	}
181 
182 	/*
183 	 * Allow access for only key 0. And prevent any other modification.
184 	 */
185 	default_amr   &= ~(0x3ul << pkeyshift(0));
186 	default_iamr  &= ~(0x1ul << pkeyshift(0));
187 	default_uamor &= ~(0x3ul << pkeyshift(0));
188 	/*
189 	 * key 0 is special in that we want to consider it an allocated
190 	 * key which is preallocated. We don't allow changing AMR bits
191 	 * w.r.t key 0. But one can pkey_free(key0)
192 	 */
193 	initial_allocation_mask |= (0x1 << 0);
194 
195 	/*
196 	 * key 1 is recommended not to be used. PowerISA(3.0) page 1015,
197 	 * programming note.
198 	 */
199 	reserved_allocation_mask |= (0x1 << 1);
200 	default_uamor &= ~(0x3ul << pkeyshift(1));
201 
202 	/*
203 	 * Prevent the usage of OS reserved keys. Update UAMOR
204 	 * for those keys. Also mark the rest of the bits in the
205 	 * 32 bit mask as reserved.
206 	 */
207 	for (i = num_pkey; i < 32 ; i++) {
208 		reserved_allocation_mask |= (0x1 << i);
209 		default_uamor &= ~(0x3ul << pkeyshift(i));
210 	}
211 	/*
212 	 * Prevent the allocation of reserved keys too.
213 	 */
214 	initial_allocation_mask |= reserved_allocation_mask;
215 
216 	pr_info("Enabling pkeys with max key count %d\n", num_pkey);
217 out:
218 	/*
219 	 * Setup uamor on boot cpu
220 	 */
221 	mtspr(SPRN_UAMOR, default_uamor);
222 
223 	return;
224 }
225 
226 void pkey_mm_init(struct mm_struct *mm)
227 {
228 	if (!mmu_has_feature(MMU_FTR_PKEY))
229 		return;
230 	mm_pkey_allocation_map(mm) = initial_allocation_mask;
231 	mm->context.execute_only_pkey = execute_only_key;
232 }
233 
234 static inline u64 read_amr(void)
235 {
236 	return mfspr(SPRN_AMR);
237 }
238 
239 static inline void write_amr(u64 value)
240 {
241 	mtspr(SPRN_AMR, value);
242 }
243 
244 static inline u64 read_iamr(void)
245 {
246 	if (!likely(pkey_execute_disable_supported))
247 		return 0x0UL;
248 
249 	return mfspr(SPRN_IAMR);
250 }
251 
252 static inline void write_iamr(u64 value)
253 {
254 	if (!likely(pkey_execute_disable_supported))
255 		return;
256 
257 	mtspr(SPRN_IAMR, value);
258 }
259 
260 static inline void init_amr(int pkey, u8 init_bits)
261 {
262 	u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
263 	u64 old_amr = read_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
264 
265 	write_amr(old_amr | new_amr_bits);
266 }
267 
268 static inline void init_iamr(int pkey, u8 init_bits)
269 {
270 	u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
271 	u64 old_iamr = read_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
272 
273 	write_iamr(old_iamr | new_iamr_bits);
274 }
275 
276 /*
277  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
278  * specified in @init_val.
279  */
280 int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
281 				unsigned long init_val)
282 {
283 	u64 new_amr_bits = 0x0ul;
284 	u64 new_iamr_bits = 0x0ul;
285 	u64 pkey_bits, uamor_pkey_bits;
286 
287 	/*
288 	 * Check whether the key is disabled by UAMOR.
289 	 */
290 	pkey_bits = 0x3ul << pkeyshift(pkey);
291 	uamor_pkey_bits = (default_uamor & pkey_bits);
292 
293 	/*
294 	 * Both the bits in UAMOR corresponding to the key should be set
295 	 */
296 	if (uamor_pkey_bits != pkey_bits)
297 		return -EINVAL;
298 
299 	if (init_val & PKEY_DISABLE_EXECUTE) {
300 		if (!pkey_execute_disable_supported)
301 			return -EINVAL;
302 		new_iamr_bits |= IAMR_EX_BIT;
303 	}
304 	init_iamr(pkey, new_iamr_bits);
305 
306 	/* Set the bits we need in AMR: */
307 	if (init_val & PKEY_DISABLE_ACCESS)
308 		new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
309 	else if (init_val & PKEY_DISABLE_WRITE)
310 		new_amr_bits |= AMR_WR_BIT;
311 
312 	init_amr(pkey, new_amr_bits);
313 	return 0;
314 }
315 
316 void thread_pkey_regs_save(struct thread_struct *thread)
317 {
318 	if (!mmu_has_feature(MMU_FTR_PKEY))
319 		return;
320 
321 	/*
322 	 * TODO: Skip saving registers if @thread hasn't used any keys yet.
323 	 */
324 	thread->amr = read_amr();
325 	thread->iamr = read_iamr();
326 }
327 
328 void thread_pkey_regs_restore(struct thread_struct *new_thread,
329 			      struct thread_struct *old_thread)
330 {
331 	if (!mmu_has_feature(MMU_FTR_PKEY))
332 		return;
333 
334 	if (old_thread->amr != new_thread->amr)
335 		write_amr(new_thread->amr);
336 	if (old_thread->iamr != new_thread->iamr)
337 		write_iamr(new_thread->iamr);
338 }
339 
340 void thread_pkey_regs_init(struct thread_struct *thread)
341 {
342 	if (!mmu_has_feature(MMU_FTR_PKEY))
343 		return;
344 
345 	thread->amr   = default_amr;
346 	thread->iamr  = default_iamr;
347 
348 	write_amr(default_amr);
349 	write_iamr(default_iamr);
350 }
351 
352 int execute_only_pkey(struct mm_struct *mm)
353 {
354 	return mm->context.execute_only_pkey;
355 }
356 
357 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
358 {
359 	/* Do this check first since the vm_flags should be hot */
360 	if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC)
361 		return false;
362 
363 	return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
364 }
365 
366 /*
367  * This should only be called for *plain* mprotect calls.
368  */
369 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
370 				  int pkey)
371 {
372 	/*
373 	 * If the currently associated pkey is execute-only, but the requested
374 	 * protection is not execute-only, move it back to the default pkey.
375 	 */
376 	if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
377 		return 0;
378 
379 	/*
380 	 * The requested protection is execute-only. Hence let's use an
381 	 * execute-only pkey.
382 	 */
383 	if (prot == PROT_EXEC) {
384 		pkey = execute_only_pkey(vma->vm_mm);
385 		if (pkey > 0)
386 			return pkey;
387 	}
388 
389 	/* Nothing to override. */
390 	return vma_pkey(vma);
391 }
392 
393 static bool pkey_access_permitted(int pkey, bool write, bool execute)
394 {
395 	int pkey_shift;
396 	u64 amr;
397 
398 	pkey_shift = pkeyshift(pkey);
399 	if (execute)
400 		return !(read_iamr() & (IAMR_EX_BIT << pkey_shift));
401 
402 	amr = read_amr();
403 	if (write)
404 		return !(amr & (AMR_WR_BIT << pkey_shift));
405 
406 	return !(amr & (AMR_RD_BIT << pkey_shift));
407 }
408 
409 bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
410 {
411 	if (!mmu_has_feature(MMU_FTR_PKEY))
412 		return true;
413 
414 	return pkey_access_permitted(pte_to_pkey_bits(pte), write, execute);
415 }
416 
417 /*
418  * We only want to enforce protection keys on the current thread because we
419  * effectively have no access to AMR/IAMR for other threads or any way to tell
420  * which AMR/IAMR in a threaded process we could use.
421  *
422  * So do not enforce things if the VMA is not from the current mm, or if we are
423  * in a kernel thread.
424  */
425 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
426 			       bool execute, bool foreign)
427 {
428 	if (!mmu_has_feature(MMU_FTR_PKEY))
429 		return true;
430 	/*
431 	 * Do not enforce our key-permissions on a foreign vma.
432 	 */
433 	if (foreign || vma_is_foreign(vma))
434 		return true;
435 
436 	return pkey_access_permitted(vma_pkey(vma), write, execute);
437 }
438 
439 void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
440 {
441 	if (!mmu_has_feature(MMU_FTR_PKEY))
442 		return;
443 
444 	/* Duplicate the oldmm pkey state in mm: */
445 	mm_pkey_allocation_map(mm) = mm_pkey_allocation_map(oldmm);
446 	mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
447 }
448