xref: /openbmc/linux/arch/arm64/kvm/hyp/nvhe/stacktrace.c (revision 53f9cd5c)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * KVM nVHE hypervisor stack tracing support.
4  *
5  * Copyright (C) 2022 Google LLC
6  */
7 #include <asm/kvm_asm.h>
8 #include <asm/kvm_hyp.h>
9 #include <asm/memory.h>
10 #include <asm/percpu.h>
11 
12 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
13 	__aligned(16);
14 
15 DEFINE_PER_CPU(struct kvm_nvhe_stacktrace_info, kvm_stacktrace_info);
16 
17 /*
18  * hyp_prepare_backtrace - Prepare non-protected nVHE backtrace.
19  *
20  * @fp : frame pointer at which to start the unwinding.
21  * @pc : program counter at which to start the unwinding.
22  *
23  * Save the information needed by the host to unwind the non-protected
24  * nVHE hypervisor stack in EL1.
25  */
26 static void hyp_prepare_backtrace(unsigned long fp, unsigned long pc)
27 {
28 	struct kvm_nvhe_stacktrace_info *stacktrace_info = this_cpu_ptr(&kvm_stacktrace_info);
29 	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
30 
31 	stacktrace_info->stack_base = (unsigned long)(params->stack_hyp_va - PAGE_SIZE);
32 	stacktrace_info->overflow_stack_base = (unsigned long)this_cpu_ptr(overflow_stack);
33 	stacktrace_info->fp = fp;
34 	stacktrace_info->pc = pc;
35 }
36 
37 #ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
38 #include <asm/stacktrace/nvhe.h>
39 
40 DEFINE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm_stacktrace);
41 
42 static bool on_overflow_stack(unsigned long sp, unsigned long size,
43 			      struct stack_info *info)
44 {
45 	unsigned long low = (unsigned long)this_cpu_ptr(overflow_stack);
46 	unsigned long high = low + OVERFLOW_STACK_SIZE;
47 
48 	return on_stack(sp, size, low, high, STACK_TYPE_OVERFLOW, info);
49 }
50 
51 static bool on_hyp_stack(unsigned long sp, unsigned long size,
52 			      struct stack_info *info)
53 {
54 	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
55 	unsigned long high = params->stack_hyp_va;
56 	unsigned long low = high - PAGE_SIZE;
57 
58 	return on_stack(sp, size, low, high, STACK_TYPE_HYP, info);
59 }
60 
61 static bool on_accessible_stack(const struct task_struct *tsk,
62 				unsigned long sp, unsigned long size,
63 				struct stack_info *info)
64 {
65 	if (info)
66 		info->type = STACK_TYPE_UNKNOWN;
67 
68 	return (on_overflow_stack(sp, size, info) ||
69 		on_hyp_stack(sp, size, info));
70 }
71 
72 static int unwind_next(struct unwind_state *state)
73 {
74 	struct stack_info info;
75 
76 	return unwind_next_common(state, &info, on_accessible_stack, NULL);
77 }
78 
79 static void notrace unwind(struct unwind_state *state,
80 			   stack_trace_consume_fn consume_entry,
81 			   void *cookie)
82 {
83 	while (1) {
84 		int ret;
85 
86 		if (!consume_entry(cookie, state->pc))
87 			break;
88 		ret = unwind_next(state);
89 		if (ret < 0)
90 			break;
91 	}
92 }
93 
94 /*
95  * pkvm_save_backtrace_entry - Saves a protected nVHE HYP stacktrace entry
96  *
97  * @arg    : index of the entry in the stacktrace buffer
98  * @where  : the program counter corresponding to the stack frame
99  *
100  * Save the return address of a stack frame to the shared stacktrace buffer.
101  * The host can access this shared buffer from EL1 to dump the backtrace.
102  */
103 static bool pkvm_save_backtrace_entry(void *arg, unsigned long where)
104 {
105 	unsigned long *stacktrace = this_cpu_ptr(pkvm_stacktrace);
106 	int *idx = (int *)arg;
107 
108 	/*
109 	 * Need 2 free slots: 1 for current entry and 1 for the
110 	 * delimiter.
111 	 */
112 	if (*idx > ARRAY_SIZE(pkvm_stacktrace) - 2)
113 		return false;
114 
115 	stacktrace[*idx] = where;
116 	stacktrace[++*idx] = 0UL;
117 
118 	return true;
119 }
120 
121 /*
122  * pkvm_save_backtrace - Saves the protected nVHE HYP stacktrace
123  *
124  * @fp : frame pointer at which to start the unwinding.
125  * @pc : program counter at which to start the unwinding.
126  *
127  * Save the unwinded stack addresses to the shared stacktrace buffer.
128  * The host can access this shared buffer from EL1 to dump the backtrace.
129  */
130 static void pkvm_save_backtrace(unsigned long fp, unsigned long pc)
131 {
132 	struct unwind_state state;
133 	int idx = 0;
134 
135 	kvm_nvhe_unwind_init(&state, fp, pc);
136 
137 	unwind(&state, pkvm_save_backtrace_entry, &idx);
138 }
139 #else /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
140 static void pkvm_save_backtrace(unsigned long fp, unsigned long pc)
141 {
142 }
143 #endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
144 
145 /*
146  * kvm_nvhe_prepare_backtrace - prepare to dump the nVHE backtrace
147  *
148  * @fp : frame pointer at which to start the unwinding.
149  * @pc : program counter at which to start the unwinding.
150  *
151  * Saves the information needed by the host to dump the nVHE hypervisor
152  * backtrace.
153  */
154 void kvm_nvhe_prepare_backtrace(unsigned long fp, unsigned long pc)
155 {
156 	if (is_protected_kvm_enabled())
157 		pkvm_save_backtrace(fp, pc);
158 	else
159 		hyp_prepare_backtrace(fp, pc);
160 }
161