1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * User-space Probes (UProbes) for powerpc
4  *
5  * Copyright IBM Corporation, 2007-2012
6  *
7  * Adapted from the x86 port by Ananth N Mavinakayanahalli <ananth@in.ibm.com>
8  */
9 #include <linux/kernel.h>
10 #include <linux/sched.h>
11 #include <linux/ptrace.h>
12 #include <linux/uprobes.h>
13 #include <linux/uaccess.h>
14 #include <linux/kdebug.h>
15 
16 #include <asm/sstep.h>
17 #include <asm/inst.h>
18 
19 #define UPROBE_TRAP_NR	UINT_MAX
20 
21 /**
22  * is_trap_insn - check if the instruction is a trap variant
23  * @insn: instruction to be checked.
24  * Returns true if @insn is a trap variant.
25  */
is_trap_insn(uprobe_opcode_t * insn)26 bool is_trap_insn(uprobe_opcode_t *insn)
27 {
28 	return (is_trap(*insn));
29 }
30 
31 /**
32  * arch_uprobe_analyze_insn
33  * @mm: the probed address space.
34  * @arch_uprobe: the probepoint information.
35  * @addr: vaddr to probe.
36  * Return 0 on success or a -ve number on error.
37  */
arch_uprobe_analyze_insn(struct arch_uprobe * auprobe,struct mm_struct * mm,unsigned long addr)38 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
39 		struct mm_struct *mm, unsigned long addr)
40 {
41 	if (addr & 0x03)
42 		return -EINVAL;
43 
44 	if (cpu_has_feature(CPU_FTR_ARCH_31) &&
45 	    ppc_inst_prefixed(ppc_inst_read(auprobe->insn)) &&
46 	    (addr & 0x3f) == 60) {
47 		pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
48 		return -EINVAL;
49 	}
50 
51 	if (!can_single_step(ppc_inst_val(ppc_inst_read(auprobe->insn)))) {
52 		pr_info_ratelimited("Cannot register a uprobe on instructions that can't be single stepped\n");
53 		return -ENOTSUPP;
54 	}
55 
56 	return 0;
57 }
58 
59 /*
60  * arch_uprobe_pre_xol - prepare to execute out of line.
61  * @auprobe: the probepoint information.
62  * @regs: reflects the saved user state of current task.
63  */
arch_uprobe_pre_xol(struct arch_uprobe * auprobe,struct pt_regs * regs)64 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
65 {
66 	struct arch_uprobe_task *autask = &current->utask->autask;
67 
68 	autask->saved_trap_nr = current->thread.trap_nr;
69 	current->thread.trap_nr = UPROBE_TRAP_NR;
70 	regs_set_return_ip(regs, current->utask->xol_vaddr);
71 
72 	user_enable_single_step(current);
73 	return 0;
74 }
75 
76 /**
77  * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
78  * @regs: Reflects the saved state of the task after it has hit a breakpoint
79  * instruction.
80  * Return the address of the breakpoint instruction.
81  */
uprobe_get_swbp_addr(struct pt_regs * regs)82 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
83 {
84 	return instruction_pointer(regs);
85 }
86 
87 /*
88  * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
89  * then detect the case where a singlestepped instruction jumps back to its
90  * own address. It is assumed that anything like do_page_fault/do_trap/etc
91  * sets thread.trap_nr != UINT_MAX.
92  *
93  * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
94  * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
95  * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
96  */
arch_uprobe_xol_was_trapped(struct task_struct * t)97 bool arch_uprobe_xol_was_trapped(struct task_struct *t)
98 {
99 	if (t->thread.trap_nr != UPROBE_TRAP_NR)
100 		return true;
101 
102 	return false;
103 }
104 
105 /*
106  * Called after single-stepping. To avoid the SMP problems that can
107  * occur when we temporarily put back the original opcode to
108  * single-step, we single-stepped a copy of the instruction.
109  *
110  * This function prepares to resume execution after the single-step.
111  */
arch_uprobe_post_xol(struct arch_uprobe * auprobe,struct pt_regs * regs)112 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
113 {
114 	struct uprobe_task *utask = current->utask;
115 
116 	WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
117 
118 	current->thread.trap_nr = utask->autask.saved_trap_nr;
119 
120 	/*
121 	 * On powerpc, except for loads and stores, most instructions
122 	 * including ones that alter code flow (branches, calls, returns)
123 	 * are emulated in the kernel. We get here only if the emulation
124 	 * support doesn't exist and have to fix-up the next instruction
125 	 * to be executed.
126 	 */
127 	regs_set_return_ip(regs, (unsigned long)ppc_inst_next((void *)utask->vaddr, auprobe->insn));
128 
129 	user_disable_single_step(current);
130 	return 0;
131 }
132 
133 /* callback routine for handling exceptions. */
arch_uprobe_exception_notify(struct notifier_block * self,unsigned long val,void * data)134 int arch_uprobe_exception_notify(struct notifier_block *self,
135 				unsigned long val, void *data)
136 {
137 	struct die_args *args = data;
138 	struct pt_regs *regs = args->regs;
139 
140 	/* regs == NULL is a kernel bug */
141 	if (WARN_ON(!regs))
142 		return NOTIFY_DONE;
143 
144 	/* We are only interested in userspace traps */
145 	if (!user_mode(regs))
146 		return NOTIFY_DONE;
147 
148 	switch (val) {
149 	case DIE_BPT:
150 		if (uprobe_pre_sstep_notifier(regs))
151 			return NOTIFY_STOP;
152 		break;
153 	case DIE_SSTEP:
154 		if (uprobe_post_sstep_notifier(regs))
155 			return NOTIFY_STOP;
156 		break;
157 	default:
158 		break;
159 	}
160 	return NOTIFY_DONE;
161 }
162 
163 /*
164  * This function gets called when XOL instruction either gets trapped or
165  * the thread has a fatal signal, so reset the instruction pointer to its
166  * probed address.
167  */
arch_uprobe_abort_xol(struct arch_uprobe * auprobe,struct pt_regs * regs)168 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
169 {
170 	struct uprobe_task *utask = current->utask;
171 
172 	current->thread.trap_nr = utask->autask.saved_trap_nr;
173 	instruction_pointer_set(regs, utask->vaddr);
174 
175 	user_disable_single_step(current);
176 }
177 
178 /*
179  * See if the instruction can be emulated.
180  * Returns true if instruction was emulated, false otherwise.
181  */
arch_uprobe_skip_sstep(struct arch_uprobe * auprobe,struct pt_regs * regs)182 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
183 {
184 	int ret;
185 
186 	/*
187 	 * emulate_step() returns 1 if the insn was successfully emulated.
188 	 * For all other cases, we need to single-step in hardware.
189 	 */
190 	ret = emulate_step(regs, ppc_inst_read(auprobe->insn));
191 	if (ret > 0)
192 		return true;
193 
194 	return false;
195 }
196 
197 unsigned long
arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,struct pt_regs * regs)198 arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
199 {
200 	unsigned long orig_ret_vaddr;
201 
202 	orig_ret_vaddr = regs->link;
203 
204 	/* Replace the return addr with trampoline addr */
205 	regs->link = trampoline_vaddr;
206 
207 	return orig_ret_vaddr;
208 }
209 
arch_uretprobe_is_alive(struct return_instance * ret,enum rp_check ctx,struct pt_regs * regs)210 bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
211 				struct pt_regs *regs)
212 {
213 	if (ctx == RP_CHECK_CHAIN_CALL)
214 		return regs->gpr[1] <= ret->stack;
215 	else
216 		return regs->gpr[1] < ret->stack;
217 }
218