xref: /openbmc/linux/arch/powerpc/mm/book3s64/pkeys.c (revision 4589a2b7)
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 				pkeys_total = 32;
94 		}
95 	}
96 
97 #ifdef CONFIG_PPC_MEM_KEYS
98 	/*
99 	 * Adjust the upper limit, based on the number of bits supported by
100 	 * arch-neutral code.
101 	 */
102 	pkeys_total = min_t(int, pkeys_total,
103 			    ((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) + 1));
104 #endif
105 	return pkeys_total;
106 }
107 
pkey_early_init_devtree(void)108 void __init pkey_early_init_devtree(void)
109 {
110 	int pkeys_total, i;
111 
112 #ifdef CONFIG_PPC_MEM_KEYS
113 	/*
114 	 * We define PKEY_DISABLE_EXECUTE in addition to the arch-neutral
115 	 * generic defines for PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
116 	 * Ensure that the bits a distinct.
117 	 */
118 	BUILD_BUG_ON(PKEY_DISABLE_EXECUTE &
119 		     (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
120 
121 	/*
122 	 * pkey_to_vmflag_bits() assumes that the pkey bits are contiguous
123 	 * in the vmaflag. Make sure that is really the case.
124 	 */
125 	BUILD_BUG_ON(__builtin_clzl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) +
126 		     __builtin_popcountl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)
127 				!= (sizeof(u64) * BITS_PER_BYTE));
128 #endif
129 	/*
130 	 * Only P7 and above supports SPRN_AMR update with MSR[PR] = 1
131 	 */
132 	if (!early_cpu_has_feature(CPU_FTR_ARCH_206))
133 		return;
134 
135 	/* scan the device tree for pkey feature */
136 	pkeys_total = scan_pkey_feature();
137 	if (!pkeys_total)
138 		goto out;
139 
140 	/* Allow all keys to be modified by default */
141 	default_uamor = ~0x0UL;
142 
143 	cur_cpu_spec->mmu_features |= MMU_FTR_PKEY;
144 
145 	/*
146 	 * The device tree cannot be relied to indicate support for
147 	 * execute_disable support. Instead we use a PVR check.
148 	 */
149 	if (pvr_version_is(PVR_POWER7) || pvr_version_is(PVR_POWER7p))
150 		pkey_execute_disable_supported = false;
151 	else
152 		pkey_execute_disable_supported = true;
153 
154 #ifdef CONFIG_PPC_4K_PAGES
155 	/*
156 	 * The OS can manage only 8 pkeys due to its inability to represent them
157 	 * in the Linux 4K PTE. Mark all other keys reserved.
158 	 */
159 	num_pkey = min(8, pkeys_total);
160 #else
161 	num_pkey = pkeys_total;
162 #endif
163 
164 	if (unlikely(num_pkey <= execute_only_key) || !pkey_execute_disable_supported) {
165 		/*
166 		 * Insufficient number of keys to support
167 		 * execute only key. Mark it unavailable.
168 		 */
169 		execute_only_key = -1;
170 	} else {
171 		/*
172 		 * Mark the execute_only_pkey as not available for
173 		 * user allocation via pkey_alloc.
174 		 */
175 		reserved_allocation_mask |= (0x1 << execute_only_key);
176 
177 		/*
178 		 * Deny READ/WRITE for execute_only_key.
179 		 * Allow execute in IAMR.
180 		 */
181 		default_amr  |= (0x3ul << pkeyshift(execute_only_key));
182 		default_iamr &= ~(0x1ul << pkeyshift(execute_only_key));
183 
184 		/*
185 		 * Clear the uamor bits for this key.
186 		 */
187 		default_uamor &= ~(0x3ul << pkeyshift(execute_only_key));
188 	}
189 
190 	if (unlikely(num_pkey <= 3)) {
191 		/*
192 		 * Insufficient number of keys to support
193 		 * KUAP/KUEP feature.
194 		 */
195 		disable_kuep = true;
196 		disable_kuap = true;
197 		WARN(1, "Disabling kernel user protection due to low (%d) max supported keys\n", num_pkey);
198 	} else {
199 		/*  handle key which is used by kernel for KAUP */
200 		reserved_allocation_mask |= (0x1 << 3);
201 		/*
202 		 * Mark access for kup_key in default amr so that
203 		 * we continue to operate with that AMR in
204 		 * copy_to/from_user().
205 		 */
206 		default_amr   &= ~(0x3ul << pkeyshift(3));
207 		default_iamr  &= ~(0x1ul << pkeyshift(3));
208 		default_uamor &= ~(0x3ul << pkeyshift(3));
209 	}
210 
211 	/*
212 	 * Allow access for only key 0. And prevent any other modification.
213 	 */
214 	default_amr   &= ~(0x3ul << pkeyshift(0));
215 	default_iamr  &= ~(0x1ul << pkeyshift(0));
216 	default_uamor &= ~(0x3ul << pkeyshift(0));
217 	/*
218 	 * key 0 is special in that we want to consider it an allocated
219 	 * key which is preallocated. We don't allow changing AMR bits
220 	 * w.r.t key 0. But one can pkey_free(key0)
221 	 */
222 	initial_allocation_mask |= (0x1 << 0);
223 
224 	/*
225 	 * key 1 is recommended not to be used. PowerISA(3.0) page 1015,
226 	 * programming note.
227 	 */
228 	reserved_allocation_mask |= (0x1 << 1);
229 	default_uamor &= ~(0x3ul << pkeyshift(1));
230 
231 	/*
232 	 * Prevent the usage of OS reserved keys. Update UAMOR
233 	 * for those keys. Also mark the rest of the bits in the
234 	 * 32 bit mask as reserved.
235 	 */
236 	for (i = num_pkey; i < 32 ; i++) {
237 		reserved_allocation_mask |= (0x1 << i);
238 		default_uamor &= ~(0x3ul << pkeyshift(i));
239 	}
240 	/*
241 	 * Prevent the allocation of reserved keys too.
242 	 */
243 	initial_allocation_mask |= reserved_allocation_mask;
244 
245 	pr_info("Enabling pkeys with max key count %d\n", num_pkey);
246 out:
247 	/*
248 	 * Setup uamor on boot cpu
249 	 */
250 	mtspr(SPRN_UAMOR, default_uamor);
251 
252 	return;
253 }
254 
255 #ifdef CONFIG_PPC_KUEP
setup_kuep(bool disabled)256 void setup_kuep(bool disabled)
257 {
258 	if (disabled)
259 		return;
260 	/*
261 	 * On hash if PKEY feature is not enabled, disable KUAP too.
262 	 */
263 	if (!early_radix_enabled() && !early_mmu_has_feature(MMU_FTR_PKEY))
264 		return;
265 
266 	if (smp_processor_id() == boot_cpuid) {
267 		pr_info("Activating Kernel Userspace Execution Prevention\n");
268 		cur_cpu_spec->mmu_features |= MMU_FTR_BOOK3S_KUEP;
269 	}
270 
271 	/*
272 	 * Radix always uses key0 of the IAMR to determine if an access is
273 	 * allowed. We set bit 0 (IBM bit 1) of key0, to prevent instruction
274 	 * fetch.
275 	 */
276 	mtspr(SPRN_IAMR, AMR_KUEP_BLOCKED);
277 	isync();
278 }
279 #endif
280 
281 #ifdef CONFIG_PPC_KUAP
setup_kuap(bool disabled)282 void setup_kuap(bool disabled)
283 {
284 	if (disabled)
285 		return;
286 	/*
287 	 * On hash if PKEY feature is not enabled, disable KUAP too.
288 	 */
289 	if (!early_radix_enabled() && !early_mmu_has_feature(MMU_FTR_PKEY))
290 		return;
291 
292 	if (smp_processor_id() == boot_cpuid) {
293 		pr_info("Activating Kernel Userspace Access Prevention\n");
294 		cur_cpu_spec->mmu_features |= MMU_FTR_KUAP;
295 	}
296 
297 	/*
298 	 * Set the default kernel AMR values on all cpus.
299 	 */
300 	mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
301 	isync();
302 }
303 #endif
304 
305 #ifdef CONFIG_PPC_MEM_KEYS
pkey_mm_init(struct mm_struct * mm)306 void pkey_mm_init(struct mm_struct *mm)
307 {
308 	if (!mmu_has_feature(MMU_FTR_PKEY))
309 		return;
310 	mm_pkey_allocation_map(mm) = initial_allocation_mask;
311 	mm->context.execute_only_pkey = execute_only_key;
312 }
313 
init_amr(int pkey,u8 init_bits)314 static inline void init_amr(int pkey, u8 init_bits)
315 {
316 	u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
317 	u64 old_amr = current_thread_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
318 
319 	current->thread.regs->amr = old_amr | new_amr_bits;
320 }
321 
init_iamr(int pkey,u8 init_bits)322 static inline void init_iamr(int pkey, u8 init_bits)
323 {
324 	u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
325 	u64 old_iamr = current_thread_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
326 
327 	if (!likely(pkey_execute_disable_supported))
328 		return;
329 
330 	current->thread.regs->iamr = old_iamr | new_iamr_bits;
331 }
332 
333 /*
334  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
335  * specified in @init_val.
336  */
__arch_set_user_pkey_access(struct task_struct * tsk,int pkey,unsigned long init_val)337 int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
338 				unsigned long init_val)
339 {
340 	u64 new_amr_bits = 0x0ul;
341 	u64 new_iamr_bits = 0x0ul;
342 	u64 pkey_bits, uamor_pkey_bits;
343 
344 	/*
345 	 * Check whether the key is disabled by UAMOR.
346 	 */
347 	pkey_bits = 0x3ul << pkeyshift(pkey);
348 	uamor_pkey_bits = (default_uamor & pkey_bits);
349 
350 	/*
351 	 * Both the bits in UAMOR corresponding to the key should be set
352 	 */
353 	if (uamor_pkey_bits != pkey_bits)
354 		return -EINVAL;
355 
356 	if (init_val & PKEY_DISABLE_EXECUTE) {
357 		if (!pkey_execute_disable_supported)
358 			return -EINVAL;
359 		new_iamr_bits |= IAMR_EX_BIT;
360 	}
361 	init_iamr(pkey, new_iamr_bits);
362 
363 	/* Set the bits we need in AMR: */
364 	if (init_val & PKEY_DISABLE_ACCESS)
365 		new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
366 	else if (init_val & PKEY_DISABLE_WRITE)
367 		new_amr_bits |= AMR_WR_BIT;
368 
369 	init_amr(pkey, new_amr_bits);
370 	return 0;
371 }
372 
execute_only_pkey(struct mm_struct * mm)373 int execute_only_pkey(struct mm_struct *mm)
374 {
375 	return mm->context.execute_only_pkey;
376 }
377 
vma_is_pkey_exec_only(struct vm_area_struct * vma)378 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
379 {
380 	/* Do this check first since the vm_flags should be hot */
381 	if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC)
382 		return false;
383 
384 	return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
385 }
386 
387 /*
388  * This should only be called for *plain* mprotect calls.
389  */
__arch_override_mprotect_pkey(struct vm_area_struct * vma,int prot,int pkey)390 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
391 				  int pkey)
392 {
393 	/*
394 	 * If the currently associated pkey is execute-only, but the requested
395 	 * protection is not execute-only, move it back to the default pkey.
396 	 */
397 	if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
398 		return 0;
399 
400 	/*
401 	 * The requested protection is execute-only. Hence let's use an
402 	 * execute-only pkey.
403 	 */
404 	if (prot == PROT_EXEC) {
405 		pkey = execute_only_pkey(vma->vm_mm);
406 		if (pkey > 0)
407 			return pkey;
408 	}
409 
410 	/* Nothing to override. */
411 	return vma_pkey(vma);
412 }
413 
pkey_access_permitted(int pkey,bool write,bool execute)414 static bool pkey_access_permitted(int pkey, bool write, bool execute)
415 {
416 	int pkey_shift;
417 	u64 amr;
418 
419 	pkey_shift = pkeyshift(pkey);
420 	if (execute)
421 		return !(current_thread_iamr() & (IAMR_EX_BIT << pkey_shift));
422 
423 	amr = current_thread_amr();
424 	if (write)
425 		return !(amr & (AMR_WR_BIT << pkey_shift));
426 
427 	return !(amr & (AMR_RD_BIT << pkey_shift));
428 }
429 
arch_pte_access_permitted(u64 pte,bool write,bool execute)430 bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
431 {
432 	if (!mmu_has_feature(MMU_FTR_PKEY))
433 		return true;
434 
435 	return pkey_access_permitted(pte_to_pkey_bits(pte), write, execute);
436 }
437 
438 /*
439  * We only want to enforce protection keys on the current thread because we
440  * effectively have no access to AMR/IAMR for other threads or any way to tell
441  * which AMR/IAMR in a threaded process we could use.
442  *
443  * So do not enforce things if the VMA is not from the current mm, or if we are
444  * in a kernel thread.
445  */
arch_vma_access_permitted(struct vm_area_struct * vma,bool write,bool execute,bool foreign)446 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
447 			       bool execute, bool foreign)
448 {
449 	if (!mmu_has_feature(MMU_FTR_PKEY))
450 		return true;
451 	/*
452 	 * Do not enforce our key-permissions on a foreign vma.
453 	 */
454 	if (foreign || vma_is_foreign(vma))
455 		return true;
456 
457 	return pkey_access_permitted(vma_pkey(vma), write, execute);
458 }
459 
arch_dup_pkeys(struct mm_struct * oldmm,struct mm_struct * mm)460 void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
461 {
462 	if (!mmu_has_feature(MMU_FTR_PKEY))
463 		return;
464 
465 	/* Duplicate the oldmm pkey state in mm: */
466 	mm_pkey_allocation_map(mm) = mm_pkey_allocation_map(oldmm);
467 	mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
468 }
469 
470 #endif /* CONFIG_PPC_MEM_KEYS */
471