xref: /linux/arch/powerpc/mm/book3s64/pkeys.c (revision 06d07429858317ded2db7986113a9e0129cd599b)
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 <asm/smp.h>
13 #include <asm/firmware.h>
14 
15 #include <linux/pkeys.h>
16 #include <linux/of_fdt.h>
17 
18 
19 int  num_pkey;		/* Max number of pkeys supported */
20 /*
21  *  Keys marked in the reservation list cannot be allocated by  userspace
22  */
23 u32 reserved_allocation_mask __ro_after_init;
24 
25 /* Bits set for the initially allocated keys */
26 static u32 initial_allocation_mask __ro_after_init;
27 
28 /*
29  * Even if we allocate keys with sys_pkey_alloc(), we need to make sure
30  * other thread still find the access denied using the same keys.
31  */
32 u64 default_amr __ro_after_init  = ~0x0UL;
33 u64 default_iamr __ro_after_init = 0x5555555555555555UL;
34 u64 default_uamor __ro_after_init;
35 EXPORT_SYMBOL(default_amr);
36 /*
37  * Key used to implement PROT_EXEC mmap. Denies READ/WRITE
38  * We pick key 2 because 0 is special key and 1 is reserved as per ISA.
39  */
40 static int execute_only_key = 2;
41 static bool pkey_execute_disable_supported;
42 
43 
44 #define AMR_BITS_PER_PKEY 2
45 #define AMR_RD_BIT 0x1UL
46 #define AMR_WR_BIT 0x2UL
47 #define IAMR_EX_BIT 0x1UL
48 #define PKEY_REG_BITS (sizeof(u64) * 8)
49 #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
50 
dt_scan_storage_keys(unsigned long node,const char * uname,int depth,void * data)51 static int __init dt_scan_storage_keys(unsigned long node,
52 				       const char *uname, int depth,
53 				       void *data)
54 {
55 	const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
56 	const __be32 *prop;
57 	int *pkeys_total = (int *) data;
58 
59 	/* We are scanning "cpu" nodes only */
60 	if (type == NULL || strcmp(type, "cpu") != 0)
61 		return 0;
62 
63 	prop = of_get_flat_dt_prop(node, "ibm,processor-storage-keys", NULL);
64 	if (!prop)
65 		return 0;
66 	*pkeys_total = be32_to_cpu(prop[0]);
67 	return 1;
68 }
69 
scan_pkey_feature(void)70 static int __init scan_pkey_feature(void)
71 {
72 	int ret;
73 	int pkeys_total = 0;
74 
75 	/*
76 	 * Pkey is not supported with Radix translation.
77 	 */
78 	if (early_radix_enabled())
79 		return 0;
80 
81 	ret = of_scan_flat_dt(dt_scan_storage_keys, &pkeys_total);
82 	if (ret == 0) {
83 		/*
84 		 * Let's assume 32 pkeys on P8/P9 bare metal, if its not defined by device
85 		 * tree. We make this exception since some version of skiboot forgot to
86 		 * expose this property on power8/9.
87 		 */
88 		if (!firmware_has_feature(FW_FEATURE_LPAR)) {
89 			unsigned long pvr = mfspr(SPRN_PVR);
90 
91 			if (PVR_VER(pvr) == PVR_POWER8 || PVR_VER(pvr) == PVR_POWER8E ||
92 			    PVR_VER(pvr) == PVR_POWER8NVL || PVR_VER(pvr) == PVR_POWER9 ||
93 			    PVR_VER(pvr) == PVR_HX_C2000)
94 				pkeys_total = 32;
95 		}
96 	}
97 
98 #ifdef CONFIG_PPC_MEM_KEYS
99 	/*
100 	 * Adjust the upper limit, based on the number of bits supported by
101 	 * arch-neutral code.
102 	 */
103 	pkeys_total = min_t(int, pkeys_total,
104 			    ((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) + 1));
105 #endif
106 	return pkeys_total;
107 }
108 
pkey_early_init_devtree(void)109 void __init pkey_early_init_devtree(void)
110 {
111 	int pkeys_total, i;
112 
113 #ifdef CONFIG_PPC_MEM_KEYS
114 	/*
115 	 * We define PKEY_DISABLE_EXECUTE in addition to the arch-neutral
116 	 * generic defines for PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
117 	 * Ensure that the bits a distinct.
118 	 */
119 	BUILD_BUG_ON(PKEY_DISABLE_EXECUTE &
120 		     (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
121 
122 	/*
123 	 * pkey_to_vmflag_bits() assumes that the pkey bits are contiguous
124 	 * in the vmaflag. Make sure that is really the case.
125 	 */
126 	BUILD_BUG_ON(__builtin_clzl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) +
127 		     __builtin_popcountl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)
128 				!= (sizeof(u64) * BITS_PER_BYTE));
129 #endif
130 	/*
131 	 * Only P7 and above supports SPRN_AMR update with MSR[PR] = 1
132 	 */
133 	if (!early_cpu_has_feature(CPU_FTR_ARCH_206))
134 		return;
135 
136 	/* scan the device tree for pkey feature */
137 	pkeys_total = scan_pkey_feature();
138 	if (!pkeys_total)
139 		goto out;
140 
141 	/* Allow all keys to be modified by default */
142 	default_uamor = ~0x0UL;
143 
144 	cur_cpu_spec->mmu_features |= MMU_FTR_PKEY;
145 
146 	/*
147 	 * The device tree cannot be relied to indicate support for
148 	 * execute_disable support. Instead we use a PVR check.
149 	 */
150 	if (pvr_version_is(PVR_POWER7) || pvr_version_is(PVR_POWER7p))
151 		pkey_execute_disable_supported = false;
152 	else
153 		pkey_execute_disable_supported = true;
154 
155 #ifdef CONFIG_PPC_4K_PAGES
156 	/*
157 	 * The OS can manage only 8 pkeys due to its inability to represent them
158 	 * in the Linux 4K PTE. Mark all other keys reserved.
159 	 */
160 	num_pkey = min(8, pkeys_total);
161 #else
162 	num_pkey = pkeys_total;
163 #endif
164 
165 	if (unlikely(num_pkey <= execute_only_key) || !pkey_execute_disable_supported) {
166 		/*
167 		 * Insufficient number of keys to support
168 		 * execute only key. Mark it unavailable.
169 		 */
170 		execute_only_key = -1;
171 	} else {
172 		/*
173 		 * Mark the execute_only_pkey as not available for
174 		 * user allocation via pkey_alloc.
175 		 */
176 		reserved_allocation_mask |= (0x1 << execute_only_key);
177 
178 		/*
179 		 * Deny READ/WRITE for execute_only_key.
180 		 * Allow execute in IAMR.
181 		 */
182 		default_amr  |= (0x3ul << pkeyshift(execute_only_key));
183 		default_iamr &= ~(0x1ul << pkeyshift(execute_only_key));
184 
185 		/*
186 		 * Clear the uamor bits for this key.
187 		 */
188 		default_uamor &= ~(0x3ul << pkeyshift(execute_only_key));
189 	}
190 
191 	if (unlikely(num_pkey <= 3)) {
192 		/*
193 		 * Insufficient number of keys to support
194 		 * KUAP/KUEP feature.
195 		 */
196 		disable_kuep = true;
197 		disable_kuap = true;
198 		WARN(1, "Disabling kernel user protection due to low (%d) max supported keys\n", num_pkey);
199 	} else {
200 		/*  handle key which is used by kernel for KAUP */
201 		reserved_allocation_mask |= (0x1 << 3);
202 		/*
203 		 * Mark access for kup_key in default amr so that
204 		 * we continue to operate with that AMR in
205 		 * copy_to/from_user().
206 		 */
207 		default_amr   &= ~(0x3ul << pkeyshift(3));
208 		default_iamr  &= ~(0x1ul << pkeyshift(3));
209 		default_uamor &= ~(0x3ul << pkeyshift(3));
210 	}
211 
212 	/*
213 	 * Allow access for only key 0. And prevent any other modification.
214 	 */
215 	default_amr   &= ~(0x3ul << pkeyshift(0));
216 	default_iamr  &= ~(0x1ul << pkeyshift(0));
217 	default_uamor &= ~(0x3ul << pkeyshift(0));
218 	/*
219 	 * key 0 is special in that we want to consider it an allocated
220 	 * key which is preallocated. We don't allow changing AMR bits
221 	 * w.r.t key 0. But one can pkey_free(key0)
222 	 */
223 	initial_allocation_mask |= (0x1 << 0);
224 
225 	/*
226 	 * key 1 is recommended not to be used. PowerISA(3.0) page 1015,
227 	 * programming note.
228 	 */
229 	reserved_allocation_mask |= (0x1 << 1);
230 	default_uamor &= ~(0x3ul << pkeyshift(1));
231 
232 	/*
233 	 * Prevent the usage of OS reserved keys. Update UAMOR
234 	 * for those keys. Also mark the rest of the bits in the
235 	 * 32 bit mask as reserved.
236 	 */
237 	for (i = num_pkey; i < 32 ; i++) {
238 		reserved_allocation_mask |= (0x1 << i);
239 		default_uamor &= ~(0x3ul << pkeyshift(i));
240 	}
241 	/*
242 	 * Prevent the allocation of reserved keys too.
243 	 */
244 	initial_allocation_mask |= reserved_allocation_mask;
245 
246 	pr_info("Enabling pkeys with max key count %d\n", num_pkey);
247 out:
248 	/*
249 	 * Setup uamor on boot cpu
250 	 */
251 	mtspr(SPRN_UAMOR, default_uamor);
252 
253 	return;
254 }
255 
256 #ifdef CONFIG_PPC_KUEP
setup_kuep(bool disabled)257 void setup_kuep(bool disabled)
258 {
259 	if (disabled)
260 		return;
261 	/*
262 	 * On hash if PKEY feature is not enabled, disable KUAP too.
263 	 */
264 	if (!early_radix_enabled() && !early_mmu_has_feature(MMU_FTR_PKEY))
265 		return;
266 
267 	if (smp_processor_id() == boot_cpuid) {
268 		pr_info("Activating Kernel Userspace Execution Prevention\n");
269 		cur_cpu_spec->mmu_features |= MMU_FTR_BOOK3S_KUEP;
270 	}
271 
272 	/*
273 	 * Radix always uses key0 of the IAMR to determine if an access is
274 	 * allowed. We set bit 0 (IBM bit 1) of key0, to prevent instruction
275 	 * fetch.
276 	 */
277 	mtspr(SPRN_IAMR, AMR_KUEP_BLOCKED);
278 	isync();
279 }
280 #endif
281 
282 #ifdef CONFIG_PPC_KUAP
setup_kuap(bool disabled)283 void setup_kuap(bool disabled)
284 {
285 	if (disabled)
286 		return;
287 	/*
288 	 * On hash if PKEY feature is not enabled, disable KUAP too.
289 	 */
290 	if (!early_radix_enabled() && !early_mmu_has_feature(MMU_FTR_PKEY))
291 		return;
292 
293 	if (smp_processor_id() == boot_cpuid) {
294 		pr_info("Activating Kernel Userspace Access Prevention\n");
295 		cur_cpu_spec->mmu_features |= MMU_FTR_KUAP;
296 	}
297 
298 	/*
299 	 * Set the default kernel AMR values on all cpus.
300 	 */
301 	mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
302 	isync();
303 }
304 #endif
305 
306 #ifdef CONFIG_PPC_MEM_KEYS
pkey_mm_init(struct mm_struct * mm)307 void pkey_mm_init(struct mm_struct *mm)
308 {
309 	if (!mmu_has_feature(MMU_FTR_PKEY))
310 		return;
311 	mm_pkey_allocation_map(mm) = initial_allocation_mask;
312 	mm->context.execute_only_pkey = execute_only_key;
313 }
314 
init_amr(int pkey,u8 init_bits)315 static inline void init_amr(int pkey, u8 init_bits)
316 {
317 	u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
318 	u64 old_amr = current_thread_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
319 
320 	current->thread.regs->amr = old_amr | new_amr_bits;
321 }
322 
init_iamr(int pkey,u8 init_bits)323 static inline void init_iamr(int pkey, u8 init_bits)
324 {
325 	u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
326 	u64 old_iamr = current_thread_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
327 
328 	if (!likely(pkey_execute_disable_supported))
329 		return;
330 
331 	current->thread.regs->iamr = old_iamr | new_iamr_bits;
332 }
333 
334 /*
335  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
336  * specified in @init_val.
337  */
__arch_set_user_pkey_access(struct task_struct * tsk,int pkey,unsigned long init_val)338 int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
339 				unsigned long init_val)
340 {
341 	u64 new_amr_bits = 0x0ul;
342 	u64 new_iamr_bits = 0x0ul;
343 	u64 pkey_bits, uamor_pkey_bits;
344 
345 	/*
346 	 * Check whether the key is disabled by UAMOR.
347 	 */
348 	pkey_bits = 0x3ul << pkeyshift(pkey);
349 	uamor_pkey_bits = (default_uamor & pkey_bits);
350 
351 	/*
352 	 * Both the bits in UAMOR corresponding to the key should be set
353 	 */
354 	if (uamor_pkey_bits != pkey_bits)
355 		return -EINVAL;
356 
357 	if (init_val & PKEY_DISABLE_EXECUTE) {
358 		if (!pkey_execute_disable_supported)
359 			return -EINVAL;
360 		new_iamr_bits |= IAMR_EX_BIT;
361 	}
362 	init_iamr(pkey, new_iamr_bits);
363 
364 	/* Set the bits we need in AMR: */
365 	if (init_val & PKEY_DISABLE_ACCESS)
366 		new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
367 	else if (init_val & PKEY_DISABLE_WRITE)
368 		new_amr_bits |= AMR_WR_BIT;
369 
370 	init_amr(pkey, new_amr_bits);
371 	return 0;
372 }
373 
execute_only_pkey(struct mm_struct * mm)374 int execute_only_pkey(struct mm_struct *mm)
375 {
376 	return mm->context.execute_only_pkey;
377 }
378 
vma_is_pkey_exec_only(struct vm_area_struct * vma)379 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
380 {
381 	/* Do this check first since the vm_flags should be hot */
382 	if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC)
383 		return false;
384 
385 	return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
386 }
387 
388 /*
389  * This should only be called for *plain* mprotect calls.
390  */
__arch_override_mprotect_pkey(struct vm_area_struct * vma,int prot,int pkey)391 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
392 				  int pkey)
393 {
394 	/*
395 	 * If the currently associated pkey is execute-only, but the requested
396 	 * protection is not execute-only, move it back to the default pkey.
397 	 */
398 	if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
399 		return 0;
400 
401 	/*
402 	 * The requested protection is execute-only. Hence let's use an
403 	 * execute-only pkey.
404 	 */
405 	if (prot == PROT_EXEC) {
406 		pkey = execute_only_pkey(vma->vm_mm);
407 		if (pkey > 0)
408 			return pkey;
409 	}
410 
411 	/* Nothing to override. */
412 	return vma_pkey(vma);
413 }
414 
pkey_access_permitted(int pkey,bool write,bool execute)415 static bool pkey_access_permitted(int pkey, bool write, bool execute)
416 {
417 	int pkey_shift;
418 	u64 amr;
419 
420 	pkey_shift = pkeyshift(pkey);
421 	if (execute)
422 		return !(current_thread_iamr() & (IAMR_EX_BIT << pkey_shift));
423 
424 	amr = current_thread_amr();
425 	if (write)
426 		return !(amr & (AMR_WR_BIT << pkey_shift));
427 
428 	return !(amr & (AMR_RD_BIT << pkey_shift));
429 }
430 
arch_pte_access_permitted(u64 pte,bool write,bool execute)431 bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
432 {
433 	if (!mmu_has_feature(MMU_FTR_PKEY))
434 		return true;
435 
436 	return pkey_access_permitted(pte_to_pkey_bits(pte), write, execute);
437 }
438 
439 /*
440  * We only want to enforce protection keys on the current thread because we
441  * effectively have no access to AMR/IAMR for other threads or any way to tell
442  * which AMR/IAMR in a threaded process we could use.
443  *
444  * So do not enforce things if the VMA is not from the current mm, or if we are
445  * in a kernel thread.
446  */
arch_vma_access_permitted(struct vm_area_struct * vma,bool write,bool execute,bool foreign)447 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
448 			       bool execute, bool foreign)
449 {
450 	if (!mmu_has_feature(MMU_FTR_PKEY))
451 		return true;
452 	/*
453 	 * Do not enforce our key-permissions on a foreign vma.
454 	 */
455 	if (foreign || vma_is_foreign(vma))
456 		return true;
457 
458 	return pkey_access_permitted(vma_pkey(vma), write, execute);
459 }
460 
arch_dup_pkeys(struct mm_struct * oldmm,struct mm_struct * mm)461 void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
462 {
463 	if (!mmu_has_feature(MMU_FTR_PKEY))
464 		return;
465 
466 	/* Duplicate the oldmm pkey state in mm: */
467 	mm_pkey_allocation_map(mm) = mm_pkey_allocation_map(oldmm);
468 	mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
469 }
470 
471 #endif /* CONFIG_PPC_MEM_KEYS */
472