xref: /openbmc/linux/arch/powerpc/kernel/optprobes.c (revision 04ec5d57)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Code for Kernel probes Jump optimization.
4  *
5  * Copyright 2017, Anju T, IBM Corp.
6  */
7 
8 #include <linux/kprobes.h>
9 #include <linux/jump_label.h>
10 #include <linux/types.h>
11 #include <linux/slab.h>
12 #include <linux/list.h>
13 #include <asm/kprobes.h>
14 #include <asm/ptrace.h>
15 #include <asm/cacheflush.h>
16 #include <asm/code-patching.h>
17 #include <asm/sstep.h>
18 #include <asm/ppc-opcode.h>
19 #include <asm/inst.h>
20 
21 #define TMPL_CALL_HDLR_IDX	(optprobe_template_call_handler - optprobe_template_entry)
22 #define TMPL_EMULATE_IDX	(optprobe_template_call_emulate - optprobe_template_entry)
23 #define TMPL_RET_IDX		(optprobe_template_ret - optprobe_template_entry)
24 #define TMPL_OP_IDX		(optprobe_template_op_address - optprobe_template_entry)
25 #define TMPL_INSN_IDX		(optprobe_template_insn - optprobe_template_entry)
26 #define TMPL_END_IDX		(optprobe_template_end - optprobe_template_entry)
27 
28 static bool insn_page_in_use;
29 
alloc_optinsn_page(void)30 void *alloc_optinsn_page(void)
31 {
32 	if (insn_page_in_use)
33 		return NULL;
34 	insn_page_in_use = true;
35 	return &optinsn_slot;
36 }
37 
free_optinsn_page(void * page)38 void free_optinsn_page(void *page)
39 {
40 	insn_page_in_use = false;
41 }
42 
43 /*
44  * Check if we can optimize this probe. Returns NIP post-emulation if this can
45  * be optimized and 0 otherwise.
46  */
can_optimize(struct kprobe * p)47 static unsigned long can_optimize(struct kprobe *p)
48 {
49 	struct pt_regs regs;
50 	struct instruction_op op;
51 	unsigned long nip = 0;
52 	unsigned long addr = (unsigned long)p->addr;
53 
54 	/*
55 	 * kprobe placed for kretprobe during boot time
56 	 * has a 'nop' instruction, which can be emulated.
57 	 * So further checks can be skipped.
58 	 */
59 	if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
60 		return addr + sizeof(kprobe_opcode_t);
61 
62 	/*
63 	 * We only support optimizing kernel addresses, but not
64 	 * module addresses.
65 	 *
66 	 * FIXME: Optimize kprobes placed in module addresses.
67 	 */
68 	if (!is_kernel_addr(addr))
69 		return 0;
70 
71 	memset(&regs, 0, sizeof(struct pt_regs));
72 	regs.nip = addr;
73 	regs.trap = 0x0;
74 	regs.msr = MSR_KERNEL;
75 
76 	/*
77 	 * Kprobe placed in conditional branch instructions are
78 	 * not optimized, as we can't predict the nip prior with
79 	 * dummy pt_regs and can not ensure that the return branch
80 	 * from detour buffer falls in the range of address (i.e 32MB).
81 	 * A branch back from trampoline is set up in the detour buffer
82 	 * to the nip returned by the analyse_instr() here.
83 	 *
84 	 * Ensure that the instruction is not a conditional branch,
85 	 * and that can be emulated.
86 	 */
87 	if (!is_conditional_branch(ppc_inst_read(p->ainsn.insn)) &&
88 	    analyse_instr(&op, &regs, ppc_inst_read(p->ainsn.insn)) == 1) {
89 		emulate_update_regs(&regs, &op);
90 		nip = regs.nip;
91 	}
92 
93 	return nip;
94 }
95 
optimized_callback(struct optimized_kprobe * op,struct pt_regs * regs)96 static void optimized_callback(struct optimized_kprobe *op,
97 			       struct pt_regs *regs)
98 {
99 	/* This is possible if op is under delayed unoptimizing */
100 	if (kprobe_disabled(&op->kp))
101 		return;
102 
103 	preempt_disable();
104 
105 	if (kprobe_running()) {
106 		kprobes_inc_nmissed_count(&op->kp);
107 	} else {
108 		__this_cpu_write(current_kprobe, &op->kp);
109 		regs_set_return_ip(regs, (unsigned long)op->kp.addr);
110 		get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
111 		opt_pre_handler(&op->kp, regs);
112 		__this_cpu_write(current_kprobe, NULL);
113 	}
114 
115 	preempt_enable();
116 }
117 NOKPROBE_SYMBOL(optimized_callback);
118 
arch_remove_optimized_kprobe(struct optimized_kprobe * op)119 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
120 {
121 	if (op->optinsn.insn) {
122 		free_optinsn_slot(op->optinsn.insn, 1);
123 		op->optinsn.insn = NULL;
124 	}
125 }
126 
patch_imm32_load_insns(unsigned long val,int reg,kprobe_opcode_t * addr)127 static void patch_imm32_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
128 {
129 	patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HI(val))));
130 	patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
131 }
132 
133 /*
134  * Generate instructions to load provided immediate 64-bit value
135  * to register 'reg' and patch these instructions at 'addr'.
136  */
patch_imm64_load_insns(unsigned long long val,int reg,kprobe_opcode_t * addr)137 static void patch_imm64_load_insns(unsigned long long val, int reg, kprobe_opcode_t *addr)
138 {
139 	patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HIGHEST(val))));
140 	patch_instruction(addr++, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_HIGHER(val))));
141 	patch_instruction(addr++, ppc_inst(PPC_RAW_SLDI(reg, reg, 32)));
142 	patch_instruction(addr++, ppc_inst(PPC_RAW_ORIS(reg, reg, PPC_HI(val))));
143 	patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
144 }
145 
patch_imm_load_insns(unsigned long val,int reg,kprobe_opcode_t * addr)146 static void patch_imm_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
147 {
148 	if (IS_ENABLED(CONFIG_PPC64))
149 		patch_imm64_load_insns(val, reg, addr);
150 	else
151 		patch_imm32_load_insns(val, reg, addr);
152 }
153 
arch_prepare_optimized_kprobe(struct optimized_kprobe * op,struct kprobe * p)154 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
155 {
156 	ppc_inst_t branch_op_callback, branch_emulate_step, temp;
157 	unsigned long op_callback_addr, emulate_step_addr;
158 	kprobe_opcode_t *buff;
159 	long b_offset;
160 	unsigned long nip, size;
161 	int rc, i;
162 
163 	nip = can_optimize(p);
164 	if (!nip)
165 		return -EILSEQ;
166 
167 	/* Allocate instruction slot for detour buffer */
168 	buff = get_optinsn_slot();
169 	if (!buff)
170 		return -ENOMEM;
171 
172 	/*
173 	 * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
174 	 *
175 	 * The target address has to be relatively nearby, to permit use
176 	 * of branch instruction in powerpc, because the address is specified
177 	 * in an immediate field in the instruction opcode itself, ie 24 bits
178 	 * in the opcode specify the address. Therefore the address should
179 	 * be within 32MB on either side of the current instruction.
180 	 */
181 	b_offset = (unsigned long)buff - (unsigned long)p->addr;
182 	if (!is_offset_in_branch_range(b_offset))
183 		goto error;
184 
185 	/* Check if the return address is also within 32MB range */
186 	b_offset = (unsigned long)(buff + TMPL_RET_IDX) - nip;
187 	if (!is_offset_in_branch_range(b_offset))
188 		goto error;
189 
190 	/* Setup template */
191 	/* We can optimize this via patch_instruction_window later */
192 	size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
193 	pr_devel("Copying template to %p, size %lu\n", buff, size);
194 	for (i = 0; i < size; i++) {
195 		rc = patch_instruction(buff + i, ppc_inst(*(optprobe_template_entry + i)));
196 		if (rc < 0)
197 			goto error;
198 	}
199 
200 	/*
201 	 * Fixup the template with instructions to:
202 	 * 1. load the address of the actual probepoint
203 	 */
204 	patch_imm_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
205 
206 	/*
207 	 * 2. branch to optimized_callback() and emulate_step()
208 	 */
209 	op_callback_addr = ppc_kallsyms_lookup_name("optimized_callback");
210 	emulate_step_addr = ppc_kallsyms_lookup_name("emulate_step");
211 	if (!op_callback_addr || !emulate_step_addr) {
212 		WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
213 		goto error;
214 	}
215 
216 	rc = create_branch(&branch_op_callback, buff + TMPL_CALL_HDLR_IDX,
217 			   op_callback_addr, BRANCH_SET_LINK);
218 
219 	rc |= create_branch(&branch_emulate_step, buff + TMPL_EMULATE_IDX,
220 			    emulate_step_addr, BRANCH_SET_LINK);
221 
222 	if (rc)
223 		goto error;
224 
225 	patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
226 	patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);
227 
228 	/*
229 	 * 3. load instruction to be emulated into relevant register, and
230 	 */
231 	temp = ppc_inst_read(p->ainsn.insn);
232 	patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
233 
234 	/*
235 	 * 4. branch back from trampoline
236 	 */
237 	patch_branch(buff + TMPL_RET_IDX, nip, 0);
238 
239 	flush_icache_range((unsigned long)buff, (unsigned long)(&buff[TMPL_END_IDX]));
240 
241 	op->optinsn.insn = buff;
242 
243 	return 0;
244 
245 error:
246 	free_optinsn_slot(buff, 0);
247 	return -ERANGE;
248 
249 }
250 
arch_prepared_optinsn(struct arch_optimized_insn * optinsn)251 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
252 {
253 	return optinsn->insn != NULL;
254 }
255 
256 /*
257  * On powerpc, Optprobes always replaces one instruction (4 bytes
258  * aligned and 4 bytes long). It is impossible to encounter another
259  * kprobe in this address range. So always return 0.
260  */
arch_check_optimized_kprobe(struct optimized_kprobe * op)261 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
262 {
263 	return 0;
264 }
265 
arch_optimize_kprobes(struct list_head * oplist)266 void arch_optimize_kprobes(struct list_head *oplist)
267 {
268 	ppc_inst_t instr;
269 	struct optimized_kprobe *op;
270 	struct optimized_kprobe *tmp;
271 
272 	list_for_each_entry_safe(op, tmp, oplist, list) {
273 		/*
274 		 * Backup instructions which will be replaced
275 		 * by jump address
276 		 */
277 		memcpy(op->optinsn.copied_insn, op->kp.addr, RELATIVEJUMP_SIZE);
278 		create_branch(&instr, op->kp.addr, (unsigned long)op->optinsn.insn, 0);
279 		patch_instruction(op->kp.addr, instr);
280 		list_del_init(&op->list);
281 	}
282 }
283 
arch_unoptimize_kprobe(struct optimized_kprobe * op)284 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
285 {
286 	arch_arm_kprobe(&op->kp);
287 }
288 
arch_unoptimize_kprobes(struct list_head * oplist,struct list_head * done_list)289 void arch_unoptimize_kprobes(struct list_head *oplist, struct list_head *done_list)
290 {
291 	struct optimized_kprobe *op;
292 	struct optimized_kprobe *tmp;
293 
294 	list_for_each_entry_safe(op, tmp, oplist, list) {
295 		arch_unoptimize_kprobe(op);
296 		list_move(&op->list, done_list);
297 	}
298 }
299 
arch_within_optimized_kprobe(struct optimized_kprobe * op,kprobe_opcode_t * addr)300 int arch_within_optimized_kprobe(struct optimized_kprobe *op, kprobe_opcode_t *addr)
301 {
302 	return (op->kp.addr <= addr &&
303 		op->kp.addr + (RELATIVEJUMP_SIZE / sizeof(kprobe_opcode_t)) > addr);
304 }
305