xref: /linux/arch/powerpc/include/asm/book3s/64/kup.h (revision a1c613ae4c322ddd58d5a8539dbfba2a0380a8c0)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_POWERPC_BOOK3S_64_KUP_H
3 #define _ASM_POWERPC_BOOK3S_64_KUP_H
4 
5 #include <linux/const.h>
6 #include <asm/reg.h>
7 
8 #define AMR_KUAP_BLOCK_READ	UL(0x5455555555555555)
9 #define AMR_KUAP_BLOCK_WRITE	UL(0xa8aaaaaaaaaaaaaa)
10 #define AMR_KUEP_BLOCKED	UL(0x5455555555555555)
11 #define AMR_KUAP_BLOCKED	(AMR_KUAP_BLOCK_READ | AMR_KUAP_BLOCK_WRITE)
12 
13 #ifdef __ASSEMBLY__
14 
15 .macro kuap_user_restore gpr1, gpr2
16 #if defined(CONFIG_PPC_PKEY)
17 	BEGIN_MMU_FTR_SECTION_NESTED(67)
18 	b	100f  // skip_restore_amr
19 	END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_PKEY, 67)
20 	/*
21 	 * AMR and IAMR are going to be different when
22 	 * returning to userspace.
23 	 */
24 	ld	\gpr1, STACK_REGS_AMR(r1)
25 
26 	/*
27 	 * If kuap feature is not enabled, do the mtspr
28 	 * only if AMR value is different.
29 	 */
30 	BEGIN_MMU_FTR_SECTION_NESTED(68)
31 	mfspr	\gpr2, SPRN_AMR
32 	cmpd	\gpr1, \gpr2
33 	beq	99f
34 	END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_KUAP, 68)
35 
36 	isync
37 	mtspr	SPRN_AMR, \gpr1
38 99:
39 	/*
40 	 * Restore IAMR only when returning to userspace
41 	 */
42 	ld	\gpr1, STACK_REGS_IAMR(r1)
43 
44 	/*
45 	 * If kuep feature is not enabled, do the mtspr
46 	 * only if IAMR value is different.
47 	 */
48 	BEGIN_MMU_FTR_SECTION_NESTED(69)
49 	mfspr	\gpr2, SPRN_IAMR
50 	cmpd	\gpr1, \gpr2
51 	beq	100f
52 	END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_BOOK3S_KUEP, 69)
53 
54 	isync
55 	mtspr	SPRN_IAMR, \gpr1
56 
57 100: //skip_restore_amr
58 	/* No isync required, see kuap_user_restore() */
59 #endif
60 .endm
61 
62 .macro kuap_kernel_restore gpr1, gpr2
63 #if defined(CONFIG_PPC_PKEY)
64 
65 	BEGIN_MMU_FTR_SECTION_NESTED(67)
66 	/*
67 	 * AMR is going to be mostly the same since we are
68 	 * returning to the kernel. Compare and do a mtspr.
69 	 */
70 	ld	\gpr2, STACK_REGS_AMR(r1)
71 	mfspr	\gpr1, SPRN_AMR
72 	cmpd	\gpr1, \gpr2
73 	beq	100f
74 	isync
75 	mtspr	SPRN_AMR, \gpr2
76 	/*
77 	 * No isync required, see kuap_restore_amr()
78 	 * No need to restore IAMR when returning to kernel space.
79 	 */
80 100:
81 	END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 67)
82 #endif
83 .endm
84 
85 #ifdef CONFIG_PPC_KUAP
86 .macro kuap_check_amr gpr1, gpr2
87 #ifdef CONFIG_PPC_KUAP_DEBUG
88 	BEGIN_MMU_FTR_SECTION_NESTED(67)
89 	mfspr	\gpr1, SPRN_AMR
90 	/* Prevent access to userspace using any key values */
91 	LOAD_REG_IMMEDIATE(\gpr2, AMR_KUAP_BLOCKED)
92 999:	tdne	\gpr1, \gpr2
93 	EMIT_WARN_ENTRY 999b, __FILE__, __LINE__, (BUGFLAG_WARNING | BUGFLAG_ONCE)
94 	END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 67)
95 #endif
96 .endm
97 #endif
98 
99 /*
100  *	if (pkey) {
101  *
102  *		save AMR -> stack;
103  *		if (kuap) {
104  *			if (AMR != BLOCKED)
105  *				KUAP_BLOCKED -> AMR;
106  *		}
107  *		if (from_user) {
108  *			save IAMR -> stack;
109  *			if (kuep) {
110  *				KUEP_BLOCKED ->IAMR
111  *			}
112  *		}
113  *		return;
114  *	}
115  *
116  *	if (kuap) {
117  *		if (from_kernel) {
118  *			save AMR -> stack;
119  *			if (AMR != BLOCKED)
120  *				KUAP_BLOCKED -> AMR;
121  *		}
122  *
123  *	}
124  */
125 .macro kuap_save_amr_and_lock gpr1, gpr2, use_cr, msr_pr_cr
126 #if defined(CONFIG_PPC_PKEY)
127 
128 	/*
129 	 * if both pkey and kuap is disabled, nothing to do
130 	 */
131 	BEGIN_MMU_FTR_SECTION_NESTED(68)
132 	b	100f  // skip_save_amr
133 	END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_PKEY | MMU_FTR_KUAP, 68)
134 
135 	/*
136 	 * if pkey is disabled and we are entering from userspace
137 	 * don't do anything.
138 	 */
139 	BEGIN_MMU_FTR_SECTION_NESTED(67)
140 	.ifnb \msr_pr_cr
141 	/*
142 	 * Without pkey we are not changing AMR outside the kernel
143 	 * hence skip this completely.
144 	 */
145 	bne	\msr_pr_cr, 100f  // from userspace
146 	.endif
147         END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_PKEY, 67)
148 
149 	/*
150 	 * pkey is enabled or pkey is disabled but entering from kernel
151 	 */
152 	mfspr	\gpr1, SPRN_AMR
153 	std	\gpr1, STACK_REGS_AMR(r1)
154 
155 	/*
156 	 * update kernel AMR with AMR_KUAP_BLOCKED only
157 	 * if KUAP feature is enabled
158 	 */
159 	BEGIN_MMU_FTR_SECTION_NESTED(69)
160 	LOAD_REG_IMMEDIATE(\gpr2, AMR_KUAP_BLOCKED)
161 	cmpd	\use_cr, \gpr1, \gpr2
162 	beq	\use_cr, 102f
163 	/*
164 	 * We don't isync here because we very recently entered via an interrupt
165 	 */
166 	mtspr	SPRN_AMR, \gpr2
167 	isync
168 102:
169 	END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 69)
170 
171 	/*
172 	 * if entering from kernel we don't need save IAMR
173 	 */
174 	.ifnb \msr_pr_cr
175 	beq	\msr_pr_cr, 100f // from kernel space
176 	mfspr	\gpr1, SPRN_IAMR
177 	std	\gpr1, STACK_REGS_IAMR(r1)
178 
179 	/*
180 	 * update kernel IAMR with AMR_KUEP_BLOCKED only
181 	 * if KUEP feature is enabled
182 	 */
183 	BEGIN_MMU_FTR_SECTION_NESTED(70)
184 	LOAD_REG_IMMEDIATE(\gpr2, AMR_KUEP_BLOCKED)
185 	mtspr	SPRN_IAMR, \gpr2
186 	isync
187 	END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_BOOK3S_KUEP, 70)
188 	.endif
189 
190 100: // skip_save_amr
191 #endif
192 .endm
193 
194 #else /* !__ASSEMBLY__ */
195 
196 #include <linux/jump_label.h>
197 #include <linux/sched.h>
198 
199 DECLARE_STATIC_KEY_FALSE(uaccess_flush_key);
200 
201 #ifdef CONFIG_PPC_PKEY
202 
203 extern u64 __ro_after_init default_uamor;
204 extern u64 __ro_after_init default_amr;
205 extern u64 __ro_after_init default_iamr;
206 
207 #include <asm/mmu.h>
208 #include <asm/ptrace.h>
209 
210 /* usage of kthread_use_mm() should inherit the
211  * AMR value of the operating address space. But, the AMR value is
212  * thread-specific and we inherit the address space and not thread
213  * access restrictions. Because of this ignore AMR value when accessing
214  * userspace via kernel thread.
215  */
current_thread_amr(void)216 static __always_inline u64 current_thread_amr(void)
217 {
218 	if (current->thread.regs)
219 		return current->thread.regs->amr;
220 	return default_amr;
221 }
222 
current_thread_iamr(void)223 static __always_inline u64 current_thread_iamr(void)
224 {
225 	if (current->thread.regs)
226 		return current->thread.regs->iamr;
227 	return default_iamr;
228 }
229 #endif /* CONFIG_PPC_PKEY */
230 
231 #ifdef CONFIG_PPC_KUAP
232 
kuap_user_restore(struct pt_regs * regs)233 static __always_inline void kuap_user_restore(struct pt_regs *regs)
234 {
235 	bool restore_amr = false, restore_iamr = false;
236 	unsigned long amr, iamr;
237 
238 	if (!mmu_has_feature(MMU_FTR_PKEY))
239 		return;
240 
241 	if (!mmu_has_feature(MMU_FTR_KUAP)) {
242 		amr = mfspr(SPRN_AMR);
243 		if (amr != regs->amr)
244 			restore_amr = true;
245 	} else {
246 		restore_amr = true;
247 	}
248 
249 	if (!mmu_has_feature(MMU_FTR_BOOK3S_KUEP)) {
250 		iamr = mfspr(SPRN_IAMR);
251 		if (iamr != regs->iamr)
252 			restore_iamr = true;
253 	} else {
254 		restore_iamr = true;
255 	}
256 
257 
258 	if (restore_amr || restore_iamr) {
259 		isync();
260 		if (restore_amr)
261 			mtspr(SPRN_AMR, regs->amr);
262 		if (restore_iamr)
263 			mtspr(SPRN_IAMR, regs->iamr);
264 	}
265 	/*
266 	 * No isync required here because we are about to rfi
267 	 * back to previous context before any user accesses
268 	 * would be made, which is a CSI.
269 	 */
270 }
271 
__kuap_kernel_restore(struct pt_regs * regs,unsigned long amr)272 static __always_inline void __kuap_kernel_restore(struct pt_regs *regs, unsigned long amr)
273 {
274 	if (likely(regs->amr == amr))
275 		return;
276 
277 	isync();
278 	mtspr(SPRN_AMR, regs->amr);
279 	/*
280 	 * No isync required here because we are about to rfi
281 	 * back to previous context before any user accesses
282 	 * would be made, which is a CSI.
283 	 *
284 	 * No need to restore IAMR when returning to kernel space.
285 	 */
286 }
287 
__kuap_get_and_assert_locked(void)288 static __always_inline unsigned long __kuap_get_and_assert_locked(void)
289 {
290 	unsigned long amr = mfspr(SPRN_AMR);
291 
292 	if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG)) /* kuap_check_amr() */
293 		WARN_ON_ONCE(amr != AMR_KUAP_BLOCKED);
294 	return amr;
295 }
296 #define __kuap_get_and_assert_locked __kuap_get_and_assert_locked
297 
298 /* __kuap_lock() not required, book3s/64 does that in ASM */
299 
300 /*
301  * We support individually allowing read or write, but we don't support nesting
302  * because that would require an expensive read/modify write of the AMR.
303  */
304 
get_kuap(void)305 static __always_inline unsigned long get_kuap(void)
306 {
307 	/*
308 	 * We return AMR_KUAP_BLOCKED when we don't support KUAP because
309 	 * prevent_user_access_return needs to return AMR_KUAP_BLOCKED to
310 	 * cause restore_user_access to do a flush.
311 	 *
312 	 * This has no effect in terms of actually blocking things on hash,
313 	 * so it doesn't break anything.
314 	 */
315 	if (!mmu_has_feature(MMU_FTR_KUAP))
316 		return AMR_KUAP_BLOCKED;
317 
318 	return mfspr(SPRN_AMR);
319 }
320 
set_kuap(unsigned long value)321 static __always_inline void set_kuap(unsigned long value)
322 {
323 	if (!mmu_has_feature(MMU_FTR_KUAP))
324 		return;
325 
326 	/*
327 	 * ISA v3.0B says we need a CSI (Context Synchronising Instruction) both
328 	 * before and after the move to AMR. See table 6 on page 1134.
329 	 */
330 	isync();
331 	mtspr(SPRN_AMR, value);
332 	isync();
333 }
334 
335 static __always_inline bool
__bad_kuap_fault(struct pt_regs * regs,unsigned long address,bool is_write)336 __bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
337 {
338 	/*
339 	 * For radix this will be a storage protection fault (DSISR_PROTFAULT).
340 	 * For hash this will be a key fault (DSISR_KEYFAULT)
341 	 */
342 	/*
343 	 * We do have exception table entry, but accessing the
344 	 * userspace results in fault.  This could be because we
345 	 * didn't unlock the AMR or access is denied by userspace
346 	 * using a key value that blocks access. We are only interested
347 	 * in catching the use case of accessing without unlocking
348 	 * the AMR. Hence check for BLOCK_WRITE/READ against AMR.
349 	 */
350 	if (is_write) {
351 		return (regs->amr & AMR_KUAP_BLOCK_WRITE) == AMR_KUAP_BLOCK_WRITE;
352 	}
353 	return (regs->amr & AMR_KUAP_BLOCK_READ) == AMR_KUAP_BLOCK_READ;
354 }
355 
allow_user_access(void __user * to,const void __user * from,unsigned long size,unsigned long dir)356 static __always_inline void allow_user_access(void __user *to, const void __user *from,
357 					      unsigned long size, unsigned long dir)
358 {
359 	unsigned long thread_amr = 0;
360 
361 	// This is written so we can resolve to a single case at build time
362 	BUILD_BUG_ON(!__builtin_constant_p(dir));
363 
364 	if (mmu_has_feature(MMU_FTR_PKEY))
365 		thread_amr = current_thread_amr();
366 
367 	if (dir == KUAP_READ)
368 		set_kuap(thread_amr | AMR_KUAP_BLOCK_WRITE);
369 	else if (dir == KUAP_WRITE)
370 		set_kuap(thread_amr | AMR_KUAP_BLOCK_READ);
371 	else if (dir == KUAP_READ_WRITE)
372 		set_kuap(thread_amr);
373 	else
374 		BUILD_BUG();
375 }
376 
377 #else /* CONFIG_PPC_KUAP */
378 
get_kuap(void)379 static __always_inline unsigned long get_kuap(void)
380 {
381 	return AMR_KUAP_BLOCKED;
382 }
383 
set_kuap(unsigned long value)384 static __always_inline void set_kuap(unsigned long value) { }
385 
allow_user_access(void __user * to,const void __user * from,unsigned long size,unsigned long dir)386 static __always_inline void allow_user_access(void __user *to, const void __user *from,
387 					      unsigned long size, unsigned long dir)
388 { }
389 
390 #endif /* !CONFIG_PPC_KUAP */
391 
prevent_user_access(unsigned long dir)392 static __always_inline void prevent_user_access(unsigned long dir)
393 {
394 	set_kuap(AMR_KUAP_BLOCKED);
395 	if (static_branch_unlikely(&uaccess_flush_key))
396 		do_uaccess_flush();
397 }
398 
prevent_user_access_return(void)399 static __always_inline unsigned long prevent_user_access_return(void)
400 {
401 	unsigned long flags = get_kuap();
402 
403 	set_kuap(AMR_KUAP_BLOCKED);
404 	if (static_branch_unlikely(&uaccess_flush_key))
405 		do_uaccess_flush();
406 
407 	return flags;
408 }
409 
restore_user_access(unsigned long flags)410 static __always_inline void restore_user_access(unsigned long flags)
411 {
412 	set_kuap(flags);
413 	if (static_branch_unlikely(&uaccess_flush_key) && flags == AMR_KUAP_BLOCKED)
414 		do_uaccess_flush();
415 }
416 #endif /* __ASSEMBLY__ */
417 
418 #endif /* _ASM_POWERPC_BOOK3S_64_KUP_H */
419