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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 | // SPDX-License-Identifier: GPL-2.0 #include <linux/static_call.h> #include <linux/memory.h> #include <linux/bug.h> #include <asm/text-patching.h> enum insn_type { CALL = 0, /* site call */ NOP = 1, /* site cond-call */ JMP = 2, /* tramp / site tail-call */ RET = 3, /* tramp / site cond-tail-call */ JCC = 4, }; /* * ud1 %esp, %ecx - a 3 byte #UD that is unique to trampolines, chosen such * that there is no false-positive trampoline identification while also being a * speculation stop. */ static const u8 tramp_ud[] = { 0x0f, 0xb9, 0xcc }; /* * cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax */ static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 }; static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc }; static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */ { u8 ret = 0; if (insn[0] == 0x0f) { u8 tmp = insn[1]; if ((tmp & 0xf0) == 0x80) ret = tmp; } return ret; } extern void __static_call_return(void); asm (".global __static_call_return\n\t" ".type __static_call_return, @function\n\t" "__static_call_return:\n\t" ANNOTATE_NOENDBR ANNOTATE_RETPOLINE_SAFE "ret; int3\n\t" ".size __static_call_return, . - __static_call_return \n\t"); static void __ref __static_call_transform(void *insn, enum insn_type type, void *func, bool modinit) { const void *emulate = NULL; int size = CALL_INSN_SIZE; const void *code; u8 op, buf[6]; if ((type == JMP || type == RET) && (op = __is_Jcc(insn))) type = JCC; switch (type) { case CALL: code = text_gen_insn(CALL_INSN_OPCODE, insn, func); if (func == &__static_call_return0) { emulate = code; code = &xor5rax; } break; case NOP: code = x86_nops[5]; break; case JMP: code = text_gen_insn(JMP32_INSN_OPCODE, insn, func); break; case RET: if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk); else code = &retinsn; break; case JCC: if (!func) { func = __static_call_return; if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) func = __x86_return_thunk; } buf[0] = 0x0f; __text_gen_insn(buf+1, op, insn+1, func, 5); code = buf; size = 6; break; } if (memcmp(insn, code, size) == 0) return; if (system_state == SYSTEM_BOOTING || modinit) return text_poke_early(insn, code, size); text_poke_bp(insn, code, size, emulate); } static void __static_call_validate(u8 *insn, bool tail, bool tramp) { u8 opcode = insn[0]; if (tramp && memcmp(insn+5, tramp_ud, 3)) { pr_err("trampoline signature fail"); BUG(); } if (tail) { if (opcode == JMP32_INSN_OPCODE || opcode == RET_INSN_OPCODE || __is_Jcc(insn)) return; } else { if (opcode == CALL_INSN_OPCODE || !memcmp(insn, x86_nops[5], 5) || !memcmp(insn, xor5rax, 5)) return; } /* * If we ever trigger this, our text is corrupt, we'll probably not live long. */ pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn); BUG(); } static inline enum insn_type __sc_insn(bool null, bool tail) { /* * Encode the following table without branches: * * tail null insn * -----+-------+------ * 0 | 0 | CALL * 0 | 1 | NOP * 1 | 0 | JMP * 1 | 1 | RET */ return 2*tail + null; } void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) { mutex_lock(&text_mutex); if (tramp) { __static_call_validate(tramp, true, true); __static_call_transform(tramp, __sc_insn(!func, true), func, false); } if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) { __static_call_validate(site, tail, false); __static_call_transform(site, __sc_insn(!func, tail), func, false); } mutex_unlock(&text_mutex); } EXPORT_SYMBOL_GPL(arch_static_call_transform); #ifdef CONFIG_RETHUNK /* * This is called by apply_returns() to fix up static call trampolines, * specifically ARCH_DEFINE_STATIC_CALL_NULL_TRAMP which is recorded as * having a return trampoline. * * The problem is that static_call() is available before determining * X86_FEATURE_RETHUNK and, by implication, running alternatives. * * This means that __static_call_transform() above can have overwritten the * return trampoline and we now need to fix things up to be consistent. */ bool __static_call_fixup(void *tramp, u8 op, void *dest) { unsigned long addr = (unsigned long)tramp; /* * Not all .return_sites are a static_call trampoline (most are not). * Check if the 3 bytes after the return are still kernel text, if not, * then this definitely is not a trampoline and we need not worry * further. * * This avoids the memcmp() below tripping over pagefaults etc.. */ if (((addr >> PAGE_SHIFT) != ((addr + 7) >> PAGE_SHIFT)) && !kernel_text_address(addr + 7)) return false; if (memcmp(tramp+5, tramp_ud, 3)) { /* Not a trampoline site, not our problem. */ return false; } mutex_lock(&text_mutex); if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk) __static_call_transform(tramp, RET, NULL, true); mutex_unlock(&text_mutex); return true; } #endif |