1 /* SPDX-License-Identifier: GPL-2.0 */ 2 3 #ifndef _ASM_X86_NOSPEC_BRANCH_H_ 4 #define _ASM_X86_NOSPEC_BRANCH_H_ 5 6 #include <linux/static_key.h> 7 #include <linux/objtool.h> 8 9 #include <asm/alternative.h> 10 #include <asm/alternative-asm.h> 11 #include <asm/cpufeatures.h> 12 #include <asm/msr-index.h> 13 #include <asm/unwind_hints.h> 14 15 /* 16 * Fill the CPU return stack buffer. 17 * 18 * Each entry in the RSB, if used for a speculative 'ret', contains an 19 * infinite 'pause; lfence; jmp' loop to capture speculative execution. 20 * 21 * This is required in various cases for retpoline and IBRS-based 22 * mitigations for the Spectre variant 2 vulnerability. Sometimes to 23 * eliminate potentially bogus entries from the RSB, and sometimes 24 * purely to ensure that it doesn't get empty, which on some CPUs would 25 * allow predictions from other (unwanted!) sources to be used. 26 * 27 * We define a CPP macro such that it can be used from both .S files and 28 * inline assembly. It's possible to do a .macro and then include that 29 * from C via asm(".include <asm/nospec-branch.h>") but let's not go there. 30 */ 31 32 #define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */ 33 34 /* 35 * Google experimented with loop-unrolling and this turned out to be 36 * the optimal version — two calls, each with their own speculation 37 * trap should their return address end up getting used, in a loop. 38 */ 39 #define __FILL_RETURN_BUFFER(reg, nr, sp) \ 40 mov $(nr/2), reg; \ 41 771: \ 42 ANNOTATE_INTRA_FUNCTION_CALL; \ 43 call 772f; \ 44 773: /* speculation trap */ \ 45 UNWIND_HINT_EMPTY; \ 46 pause; \ 47 lfence; \ 48 jmp 773b; \ 49 772: \ 50 ANNOTATE_INTRA_FUNCTION_CALL; \ 51 call 774f; \ 52 775: /* speculation trap */ \ 53 UNWIND_HINT_EMPTY; \ 54 pause; \ 55 lfence; \ 56 jmp 775b; \ 57 774: \ 58 add $(BITS_PER_LONG/8) * 2, sp; \ 59 dec reg; \ 60 jnz 771b; 61 62 #ifdef __ASSEMBLY__ 63 64 /* 65 * This should be used immediately before an indirect jump/call. It tells 66 * objtool the subsequent indirect jump/call is vouched safe for retpoline 67 * builds. 68 */ 69 .macro ANNOTATE_RETPOLINE_SAFE 70 .Lannotate_\@: 71 .pushsection .discard.retpoline_safe 72 _ASM_PTR .Lannotate_\@ 73 .popsection 74 .endm 75 76 /* 77 * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple 78 * indirect jmp/call which may be susceptible to the Spectre variant 2 79 * attack. 80 */ 81 .macro JMP_NOSPEC reg:req 82 #ifdef CONFIG_RETPOLINE 83 ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ 84 __stringify(jmp __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \ 85 __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD 86 #else 87 jmp *%\reg 88 #endif 89 .endm 90 91 .macro CALL_NOSPEC reg:req 92 #ifdef CONFIG_RETPOLINE 93 ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \ 94 __stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \ 95 __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD 96 #else 97 call *%\reg 98 #endif 99 .endm 100 101 /* 102 * A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP 103 * monstrosity above, manually. 104 */ 105 .macro FILL_RETURN_BUFFER reg:req nr:req ftr:req 106 #ifdef CONFIG_RETPOLINE 107 ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr 108 __FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP) 109 .Lskip_rsb_\@: 110 #endif 111 .endm 112 113 #else /* __ASSEMBLY__ */ 114 115 #define ANNOTATE_RETPOLINE_SAFE \ 116 "999:\n\t" \ 117 ".pushsection .discard.retpoline_safe\n\t" \ 118 _ASM_PTR " 999b\n\t" \ 119 ".popsection\n\t" 120 121 #ifdef CONFIG_RETPOLINE 122 #ifdef CONFIG_X86_64 123 124 /* 125 * Inline asm uses the %V modifier which is only in newer GCC 126 * which is ensured when CONFIG_RETPOLINE is defined. 127 */ 128 # define CALL_NOSPEC \ 129 ALTERNATIVE_2( \ 130 ANNOTATE_RETPOLINE_SAFE \ 131 "call *%[thunk_target]\n", \ 132 "call __x86_retpoline_%V[thunk_target]\n", \ 133 X86_FEATURE_RETPOLINE, \ 134 "lfence;\n" \ 135 ANNOTATE_RETPOLINE_SAFE \ 136 "call *%[thunk_target]\n", \ 137 X86_FEATURE_RETPOLINE_AMD) 138 139 # define THUNK_TARGET(addr) [thunk_target] "r" (addr) 140 141 #else /* CONFIG_X86_32 */ 142 /* 143 * For i386 we use the original ret-equivalent retpoline, because 144 * otherwise we'll run out of registers. We don't care about CET 145 * here, anyway. 146 */ 147 # define CALL_NOSPEC \ 148 ALTERNATIVE_2( \ 149 ANNOTATE_RETPOLINE_SAFE \ 150 "call *%[thunk_target]\n", \ 151 " jmp 904f;\n" \ 152 " .align 16\n" \ 153 "901: call 903f;\n" \ 154 "902: pause;\n" \ 155 " lfence;\n" \ 156 " jmp 902b;\n" \ 157 " .align 16\n" \ 158 "903: lea 4(%%esp), %%esp;\n" \ 159 " pushl %[thunk_target];\n" \ 160 " ret;\n" \ 161 " .align 16\n" \ 162 "904: call 901b;\n", \ 163 X86_FEATURE_RETPOLINE, \ 164 "lfence;\n" \ 165 ANNOTATE_RETPOLINE_SAFE \ 166 "call *%[thunk_target]\n", \ 167 X86_FEATURE_RETPOLINE_AMD) 168 169 # define THUNK_TARGET(addr) [thunk_target] "rm" (addr) 170 #endif 171 #else /* No retpoline for C / inline asm */ 172 # define CALL_NOSPEC "call *%[thunk_target]\n" 173 # define THUNK_TARGET(addr) [thunk_target] "rm" (addr) 174 #endif 175 176 /* The Spectre V2 mitigation variants */ 177 enum spectre_v2_mitigation { 178 SPECTRE_V2_NONE, 179 SPECTRE_V2_RETPOLINE_GENERIC, 180 SPECTRE_V2_RETPOLINE_AMD, 181 SPECTRE_V2_IBRS_ENHANCED, 182 }; 183 184 /* The indirect branch speculation control variants */ 185 enum spectre_v2_user_mitigation { 186 SPECTRE_V2_USER_NONE, 187 SPECTRE_V2_USER_STRICT, 188 SPECTRE_V2_USER_STRICT_PREFERRED, 189 SPECTRE_V2_USER_PRCTL, 190 SPECTRE_V2_USER_SECCOMP, 191 }; 192 193 /* The Speculative Store Bypass disable variants */ 194 enum ssb_mitigation { 195 SPEC_STORE_BYPASS_NONE, 196 SPEC_STORE_BYPASS_DISABLE, 197 SPEC_STORE_BYPASS_PRCTL, 198 SPEC_STORE_BYPASS_SECCOMP, 199 }; 200 201 extern char __indirect_thunk_start[]; 202 extern char __indirect_thunk_end[]; 203 204 static __always_inline 205 void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature) 206 { 207 asm volatile(ALTERNATIVE("", "wrmsr", %c[feature]) 208 : : "c" (msr), 209 "a" ((u32)val), 210 "d" ((u32)(val >> 32)), 211 [feature] "i" (feature) 212 : "memory"); 213 } 214 215 static inline void indirect_branch_prediction_barrier(void) 216 { 217 u64 val = PRED_CMD_IBPB; 218 219 alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB); 220 } 221 222 /* The Intel SPEC CTRL MSR base value cache */ 223 extern u64 x86_spec_ctrl_base; 224 225 /* 226 * With retpoline, we must use IBRS to restrict branch prediction 227 * before calling into firmware. 228 * 229 * (Implemented as CPP macros due to header hell.) 230 */ 231 #define firmware_restrict_branch_speculation_start() \ 232 do { \ 233 u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS; \ 234 \ 235 preempt_disable(); \ 236 alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \ 237 X86_FEATURE_USE_IBRS_FW); \ 238 } while (0) 239 240 #define firmware_restrict_branch_speculation_end() \ 241 do { \ 242 u64 val = x86_spec_ctrl_base; \ 243 \ 244 alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \ 245 X86_FEATURE_USE_IBRS_FW); \ 246 preempt_enable(); \ 247 } while (0) 248 249 DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); 250 DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); 251 DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); 252 253 DECLARE_STATIC_KEY_FALSE(mds_user_clear); 254 DECLARE_STATIC_KEY_FALSE(mds_idle_clear); 255 256 #include <asm/segment.h> 257 258 /** 259 * mds_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability 260 * 261 * This uses the otherwise unused and obsolete VERW instruction in 262 * combination with microcode which triggers a CPU buffer flush when the 263 * instruction is executed. 264 */ 265 static __always_inline void mds_clear_cpu_buffers(void) 266 { 267 static const u16 ds = __KERNEL_DS; 268 269 /* 270 * Has to be the memory-operand variant because only that 271 * guarantees the CPU buffer flush functionality according to 272 * documentation. The register-operand variant does not. 273 * Works with any segment selector, but a valid writable 274 * data segment is the fastest variant. 275 * 276 * "cc" clobber is required because VERW modifies ZF. 277 */ 278 asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc"); 279 } 280 281 /** 282 * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability 283 * 284 * Clear CPU buffers if the corresponding static key is enabled 285 */ 286 static __always_inline void mds_user_clear_cpu_buffers(void) 287 { 288 if (static_branch_likely(&mds_user_clear)) 289 mds_clear_cpu_buffers(); 290 } 291 292 /** 293 * mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability 294 * 295 * Clear CPU buffers if the corresponding static key is enabled 296 */ 297 static inline void mds_idle_clear_cpu_buffers(void) 298 { 299 if (static_branch_likely(&mds_idle_clear)) 300 mds_clear_cpu_buffers(); 301 } 302 303 #endif /* __ASSEMBLY__ */ 304 305 /* 306 * Below is used in the eBPF JIT compiler and emits the byte sequence 307 * for the following assembly: 308 * 309 * With retpolines configured: 310 * 311 * callq do_rop 312 * spec_trap: 313 * pause 314 * lfence 315 * jmp spec_trap 316 * do_rop: 317 * mov %rcx,(%rsp) for x86_64 318 * mov %edx,(%esp) for x86_32 319 * retq 320 * 321 * Without retpolines configured: 322 * 323 * jmp *%rcx for x86_64 324 * jmp *%edx for x86_32 325 */ 326 #ifdef CONFIG_RETPOLINE 327 # ifdef CONFIG_X86_64 328 # define RETPOLINE_RCX_BPF_JIT_SIZE 17 329 # define RETPOLINE_RCX_BPF_JIT() \ 330 do { \ 331 EMIT1_off32(0xE8, 7); /* callq do_rop */ \ 332 /* spec_trap: */ \ 333 EMIT2(0xF3, 0x90); /* pause */ \ 334 EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \ 335 EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \ 336 /* do_rop: */ \ 337 EMIT4(0x48, 0x89, 0x0C, 0x24); /* mov %rcx,(%rsp) */ \ 338 EMIT1(0xC3); /* retq */ \ 339 } while (0) 340 # else /* !CONFIG_X86_64 */ 341 # define RETPOLINE_EDX_BPF_JIT() \ 342 do { \ 343 EMIT1_off32(0xE8, 7); /* call do_rop */ \ 344 /* spec_trap: */ \ 345 EMIT2(0xF3, 0x90); /* pause */ \ 346 EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \ 347 EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \ 348 /* do_rop: */ \ 349 EMIT3(0x89, 0x14, 0x24); /* mov %edx,(%esp) */ \ 350 EMIT1(0xC3); /* ret */ \ 351 } while (0) 352 # endif 353 #else /* !CONFIG_RETPOLINE */ 354 # ifdef CONFIG_X86_64 355 # define RETPOLINE_RCX_BPF_JIT_SIZE 2 356 # define RETPOLINE_RCX_BPF_JIT() \ 357 EMIT2(0xFF, 0xE1); /* jmp *%rcx */ 358 # else /* !CONFIG_X86_64 */ 359 # define RETPOLINE_EDX_BPF_JIT() \ 360 EMIT2(0xFF, 0xE2) /* jmp *%edx */ 361 # endif 362 #endif 363 364 #endif /* _ASM_X86_NOSPEC_BRANCH_H_ */ 365