| 1 | /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only) |
| 2 | * |
| 3 | * wrapper/kallsyms.c |
| 4 | * |
| 5 | * Wrapper around kallsyms. Using kprobes to get its address when available. |
| 6 | * |
| 7 | * Can we mainline LTTng already so we don't have to waste our time doing this |
| 8 | * kind of hack ? |
| 9 | * |
| 10 | * Copyright (C) 2020 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 11 | */ |
| 12 | |
| 13 | #include <linux/kprobes.h> |
| 14 | #include <linux/module.h> |
| 15 | #include <wrapper/kallsyms.h> |
| 16 | |
| 17 | #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,7,0)) |
| 18 | |
| 19 | #ifndef CONFIG_KPROBES |
| 20 | # error "LTTng-modules requires CONFIG_KPROBES on kernels >= 5.7.0" |
| 21 | #endif |
| 22 | |
| 23 | static |
| 24 | unsigned long (*kallsyms_lookup_name_sym)(const char *name); |
| 25 | |
| 26 | static |
| 27 | int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs) |
| 28 | { |
| 29 | return 0; |
| 30 | } |
| 31 | |
| 32 | #ifdef LTTNG_CONFIG_PPC64_ELF_ABI_V2 |
| 33 | static |
| 34 | void kallsyms_pre_arch_adjust(struct kprobe *probe) |
| 35 | { |
| 36 | /* |
| 37 | * With powerpc64 ABIv2, we need the global entry point of |
| 38 | * kallsyms_lookup_name to call it later, while kprobe_register would |
| 39 | * automatically adjust the global entry point to the local entry point, |
| 40 | * when a kprobe was registered at a function entry. So we add 4 bytes |
| 41 | * which is the length of one instruction to kallsyms_lookup_name to |
| 42 | * avoid the adjustment. |
| 43 | */ |
| 44 | probe->offset = 4; |
| 45 | } |
| 46 | #else |
| 47 | static |
| 48 | void kallsyms_pre_arch_adjust(struct kprobe *probe) |
| 49 | { |
| 50 | } |
| 51 | #endif |
| 52 | |
| 53 | #ifdef LTTNG_CONFIG_PPC64_ELF_ABI_V2 |
| 54 | static |
| 55 | unsigned long kallsyms_get_arch_call_addr(const struct kprobe *probe) |
| 56 | { |
| 57 | /* Substract 4 bytes to get what we originally want */ |
| 58 | return (unsigned long)(((char *)probe->addr) - 4); |
| 59 | } |
| 60 | |
| 61 | #elif defined(LTTNG_CONFIG_PPC64_ELF_ABI_V1) |
| 62 | # if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,18,0)) |
| 63 | # include <asm/elf.h> |
| 64 | # define LTTNG_FUNC_DESC_TYPE struct func_desc |
| 65 | # define LTTNG_FUNC_DESC_ADDR_NAME addr |
| 66 | # else |
| 67 | # include <asm/types.h> |
| 68 | # define LTTNG_FUNC_DESC_TYPE func_descr_t |
| 69 | # define LTTNG_FUNC_DESC_ADDR_NAME entry |
| 70 | |
| 71 | static |
| 72 | LTTNG_FUNC_DESC_TYPE kallsyms_lookup_name_func_desc; |
| 73 | # endif |
| 74 | |
| 75 | static |
| 76 | unsigned long kallsyms_get_arch_call_addr(const struct kprobe *probe) |
| 77 | { |
| 78 | /* |
| 79 | * Build a function descriptor from the address of |
| 80 | * 'kallsyms_lookup_name' returned by kprobe and the toc of |
| 81 | * 'sprint_symbol' which is in the same compile unit and exported. I |
| 82 | * hate this on so many levels but it works. |
| 83 | */ |
| 84 | kallsyms_lookup_name_func_desc.LTTNG_FUNC_DESC_ADDR_NAME = (unsigned long) probe.addr; |
| 85 | kallsyms_lookup_name_func_desc.toc = ((LTTNG_FUNC_DESC_TYPE *) &sprint_symbol)->toc; |
| 86 | return (unsigned long) &kallsyms_lookup_name_func_desc; |
| 87 | } |
| 88 | #elif defined(CONFIG_ARM) && defined(CONFIG_THUMB2_KERNEL) |
| 89 | static |
| 90 | unsigned long kallsyms_get_arch_call_addr(const struct kprobe *probe) |
| 91 | { |
| 92 | unsigned long addr = (unsigned long)probe->addr; |
| 93 | |
| 94 | if (addr) |
| 95 | addr |= 1; /* set bit 0 in address for thumb mode */ |
| 96 | return addr; |
| 97 | } |
| 98 | #else |
| 99 | static |
| 100 | unsigned long kallsyms_get_arch_call_addr(const struct kprobe *probe) |
| 101 | { |
| 102 | return (unsigned long)probe->addr; |
| 103 | } |
| 104 | #endif |
| 105 | |
| 106 | static |
| 107 | unsigned long do_get_kallsyms(void) |
| 108 | { |
| 109 | struct kprobe probe; |
| 110 | int ret; |
| 111 | unsigned long addr; |
| 112 | |
| 113 | memset(&probe, 0, sizeof(probe)); |
| 114 | probe.pre_handler = dummy_kprobe_handler; |
| 115 | probe.symbol_name = "kallsyms_lookup_name"; |
| 116 | kallsyms_pre_arch_adjust(&probe); |
| 117 | ret = register_kprobe(&probe); |
| 118 | if (ret) |
| 119 | return 0; |
| 120 | addr = kallsyms_get_arch_call_addr(&probe); |
| 121 | unregister_kprobe(&probe); |
| 122 | return addr; |
| 123 | } |
| 124 | |
| 125 | unsigned long wrapper_kallsyms_lookup_name(const char *name) |
| 126 | { |
| 127 | if (!kallsyms_lookup_name_sym) { |
| 128 | kallsyms_lookup_name_sym = (void *)do_get_kallsyms(); |
| 129 | } |
| 130 | if (kallsyms_lookup_name_sym) { |
| 131 | struct irq_ibt_state irq_ibt_state; |
| 132 | unsigned long ret; |
| 133 | |
| 134 | irq_ibt_state = wrapper_irq_ibt_save(); |
| 135 | ret = kallsyms_lookup_name_sym(name); |
| 136 | wrapper_irq_ibt_restore(irq_ibt_state); |
| 137 | return ret; |
| 138 | } else { |
| 139 | printk_once(KERN_WARNING "LTTng: requires kallsyms_lookup_name\n"); |
| 140 | return 0; |
| 141 | } |
| 142 | } |
| 143 | EXPORT_SYMBOL_GPL(wrapper_kallsyms_lookup_name); |
| 144 | |
| 145 | #endif |
| 146 | |
| 147 | #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,4,0) && defined(CONFIG_ANDROID)) |
| 148 | MODULE_IMPORT_NS(VFS_internal_I_am_really_a_filesystem_and_am_NOT_a_driver); |
| 149 | #endif |