1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #include <linux/jump_label.h> 3 #include <asm/unwind_hints.h> 4 #include <asm/cpufeatures.h> 5 #include <asm/page_types.h> 6 #include <asm/percpu.h> 7 #include <asm/asm-offsets.h> 8 #include <asm/processor-flags.h> 9 #include <asm/msr.h> 10 #include <asm/nospec-branch.h> 11 12 /* 13 14 x86 function call convention, 64-bit: 15 ------------------------------------- 16 arguments | callee-saved | extra caller-saved | return 17 [callee-clobbered] | | [callee-clobbered] | 18 --------------------------------------------------------------------------- 19 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] 20 21 ( rsp is obviously invariant across normal function calls. (gcc can 'merge' 22 functions when it sees tail-call optimization possibilities) rflags is 23 clobbered. Leftover arguments are passed over the stack frame.) 24 25 [*] In the frame-pointers case rbp is fixed to the stack frame. 26 27 [**] for struct return values wider than 64 bits the return convention is a 28 bit more complex: up to 128 bits width we return small structures 29 straight in rax, rdx. For structures larger than that (3 words or 30 larger) the caller puts a pointer to an on-stack return struct 31 [allocated in the caller's stack frame] into the first argument - i.e. 32 into rdi. All other arguments shift up by one in this case. 33 Fortunately this case is rare in the kernel. 34 35 For 32-bit we have the following conventions - kernel is built with 36 -mregparm=3 and -freg-struct-return: 37 38 x86 function calling convention, 32-bit: 39 ---------------------------------------- 40 arguments | callee-saved | extra caller-saved | return 41 [callee-clobbered] | | [callee-clobbered] | 42 ------------------------------------------------------------------------- 43 eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] 44 45 ( here too esp is obviously invariant across normal function calls. eflags 46 is clobbered. Leftover arguments are passed over the stack frame. ) 47 48 [*] In the frame-pointers case ebp is fixed to the stack frame. 49 50 [**] We build with -freg-struct-return, which on 32-bit means similar 51 semantics as on 64-bit: edx can be used for a second return value 52 (i.e. covering integer and structure sizes up to 64 bits) - after that 53 it gets more complex and more expensive: 3-word or larger struct returns 54 get done in the caller's frame and the pointer to the return struct goes 55 into regparm0, i.e. eax - the other arguments shift up and the 56 function's register parameters degenerate to regparm=2 in essence. 57 58 */ 59 60 #ifdef CONFIG_X86_64 61 62 /* 63 * 64-bit system call stack frame layout defines and helpers, 64 * for assembly code: 65 */ 66 67 /* The layout forms the "struct pt_regs" on the stack: */ 68 /* 69 * C ABI says these regs are callee-preserved. They aren't saved on kernel entry 70 * unless syscall needs a complete, fully filled "struct pt_regs". 71 */ 72 #define R15 0*8 73 #define R14 1*8 74 #define R13 2*8 75 #define R12 3*8 76 #define RBP 4*8 77 #define RBX 5*8 78 /* These regs are callee-clobbered. Always saved on kernel entry. */ 79 #define R11 6*8 80 #define R10 7*8 81 #define R9 8*8 82 #define R8 9*8 83 #define RAX 10*8 84 #define RCX 11*8 85 #define RDX 12*8 86 #define RSI 13*8 87 #define RDI 14*8 88 /* 89 * On syscall entry, this is syscall#. On CPU exception, this is error code. 90 * On hw interrupt, it's IRQ number: 91 */ 92 #define ORIG_RAX 15*8 93 /* Return frame for iretq */ 94 #define RIP 16*8 95 #define CS 17*8 96 #define EFLAGS 18*8 97 #define RSP 19*8 98 #define SS 20*8 99 100 #define SIZEOF_PTREGS 21*8 101 102 .macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0 103 .if \save_ret 104 pushq %rsi /* pt_regs->si */ 105 movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */ 106 movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */ 107 .else 108 pushq %rdi /* pt_regs->di */ 109 pushq %rsi /* pt_regs->si */ 110 .endif 111 pushq \rdx /* pt_regs->dx */ 112 pushq %rcx /* pt_regs->cx */ 113 pushq \rax /* pt_regs->ax */ 114 pushq %r8 /* pt_regs->r8 */ 115 pushq %r9 /* pt_regs->r9 */ 116 pushq %r10 /* pt_regs->r10 */ 117 pushq %r11 /* pt_regs->r11 */ 118 pushq %rbx /* pt_regs->rbx */ 119 pushq %rbp /* pt_regs->rbp */ 120 pushq %r12 /* pt_regs->r12 */ 121 pushq %r13 /* pt_regs->r13 */ 122 pushq %r14 /* pt_regs->r14 */ 123 pushq %r15 /* pt_regs->r15 */ 124 UNWIND_HINT_REGS 125 126 .if \save_ret 127 pushq %rsi /* return address on top of stack */ 128 .endif 129 130 /* 131 * Sanitize registers of values that a speculation attack might 132 * otherwise want to exploit. The lower registers are likely clobbered 133 * well before they could be put to use in a speculative execution 134 * gadget. 135 */ 136 xorl %edx, %edx /* nospec dx */ 137 xorl %ecx, %ecx /* nospec cx */ 138 xorl %r8d, %r8d /* nospec r8 */ 139 xorl %r9d, %r9d /* nospec r9 */ 140 xorl %r10d, %r10d /* nospec r10 */ 141 xorl %r11d, %r11d /* nospec r11 */ 142 xorl %ebx, %ebx /* nospec rbx */ 143 xorl %ebp, %ebp /* nospec rbp */ 144 xorl %r12d, %r12d /* nospec r12 */ 145 xorl %r13d, %r13d /* nospec r13 */ 146 xorl %r14d, %r14d /* nospec r14 */ 147 xorl %r15d, %r15d /* nospec r15 */ 148 149 .endm 150 151 .macro POP_REGS pop_rdi=1 152 popq %r15 153 popq %r14 154 popq %r13 155 popq %r12 156 popq %rbp 157 popq %rbx 158 popq %r11 159 popq %r10 160 popq %r9 161 popq %r8 162 popq %rax 163 popq %rcx 164 popq %rdx 165 popq %rsi 166 .if \pop_rdi 167 popq %rdi 168 .endif 169 .endm 170 171 #ifdef CONFIG_PAGE_TABLE_ISOLATION 172 173 /* 174 * PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two 175 * halves: 176 */ 177 #define PTI_USER_PGTABLE_BIT PAGE_SHIFT 178 #define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT) 179 #define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT 180 #define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT) 181 #define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK) 182 183 .macro SET_NOFLUSH_BIT reg:req 184 bts $X86_CR3_PCID_NOFLUSH_BIT, \reg 185 .endm 186 187 .macro ADJUST_KERNEL_CR3 reg:req 188 ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID 189 /* Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */ 190 andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg 191 .endm 192 193 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 194 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 195 mov %cr3, \scratch_reg 196 ADJUST_KERNEL_CR3 \scratch_reg 197 mov \scratch_reg, %cr3 198 .Lend_\@: 199 .endm 200 201 #define THIS_CPU_user_pcid_flush_mask \ 202 PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask 203 204 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 205 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 206 mov %cr3, \scratch_reg 207 208 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 209 210 /* 211 * Test if the ASID needs a flush. 212 */ 213 movq \scratch_reg, \scratch_reg2 214 andq $(0x7FF), \scratch_reg /* mask ASID */ 215 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 216 jnc .Lnoflush_\@ 217 218 /* Flush needed, clear the bit */ 219 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 220 movq \scratch_reg2, \scratch_reg 221 jmp .Lwrcr3_pcid_\@ 222 223 .Lnoflush_\@: 224 movq \scratch_reg2, \scratch_reg 225 SET_NOFLUSH_BIT \scratch_reg 226 227 .Lwrcr3_pcid_\@: 228 /* Flip the ASID to the user version */ 229 orq $(PTI_USER_PCID_MASK), \scratch_reg 230 231 .Lwrcr3_\@: 232 /* Flip the PGD to the user version */ 233 orq $(PTI_USER_PGTABLE_MASK), \scratch_reg 234 mov \scratch_reg, %cr3 235 .Lend_\@: 236 .endm 237 238 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 239 pushq %rax 240 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax 241 popq %rax 242 .endm 243 244 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 245 ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI 246 movq %cr3, \scratch_reg 247 movq \scratch_reg, \save_reg 248 /* 249 * Test the user pagetable bit. If set, then the user page tables 250 * are active. If clear CR3 already has the kernel page table 251 * active. 252 */ 253 bt $PTI_USER_PGTABLE_BIT, \scratch_reg 254 jnc .Ldone_\@ 255 256 ADJUST_KERNEL_CR3 \scratch_reg 257 movq \scratch_reg, %cr3 258 259 .Ldone_\@: 260 .endm 261 262 .macro RESTORE_CR3 scratch_reg:req save_reg:req 263 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 264 265 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 266 267 /* 268 * KERNEL pages can always resume with NOFLUSH as we do 269 * explicit flushes. 270 */ 271 bt $PTI_USER_PGTABLE_BIT, \save_reg 272 jnc .Lnoflush_\@ 273 274 /* 275 * Check if there's a pending flush for the user ASID we're 276 * about to set. 277 */ 278 movq \save_reg, \scratch_reg 279 andq $(0x7FF), \scratch_reg 280 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 281 jnc .Lnoflush_\@ 282 283 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 284 jmp .Lwrcr3_\@ 285 286 .Lnoflush_\@: 287 SET_NOFLUSH_BIT \save_reg 288 289 .Lwrcr3_\@: 290 /* 291 * The CR3 write could be avoided when not changing its value, 292 * but would require a CR3 read *and* a scratch register. 293 */ 294 movq \save_reg, %cr3 295 .Lend_\@: 296 .endm 297 298 #else /* CONFIG_PAGE_TABLE_ISOLATION=n: */ 299 300 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 301 .endm 302 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 303 .endm 304 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 305 .endm 306 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 307 .endm 308 .macro RESTORE_CR3 scratch_reg:req save_reg:req 309 .endm 310 311 #endif 312 313 /* 314 * IBRS kernel mitigation for Spectre_v2. 315 * 316 * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers 317 * the regs it uses (AX, CX, DX). Must be called before the first RET 318 * instruction (NOTE! UNTRAIN_RET includes a RET instruction) 319 * 320 * The optional argument is used to save/restore the current value, 321 * which is used on the paranoid paths. 322 * 323 * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set. 324 */ 325 .macro IBRS_ENTER save_reg 326 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS 327 movl $MSR_IA32_SPEC_CTRL, %ecx 328 329 .ifnb \save_reg 330 rdmsr 331 shl $32, %rdx 332 or %rdx, %rax 333 mov %rax, \save_reg 334 test $SPEC_CTRL_IBRS, %eax 335 jz .Ldo_wrmsr_\@ 336 lfence 337 jmp .Lend_\@ 338 .Ldo_wrmsr_\@: 339 .endif 340 341 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx 342 movl %edx, %eax 343 shr $32, %rdx 344 wrmsr 345 .Lend_\@: 346 .endm 347 348 /* 349 * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX) 350 * regs. Must be called after the last RET. 351 */ 352 .macro IBRS_EXIT save_reg 353 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS 354 movl $MSR_IA32_SPEC_CTRL, %ecx 355 356 .ifnb \save_reg 357 mov \save_reg, %rdx 358 .else 359 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx 360 andl $(~SPEC_CTRL_IBRS), %edx 361 .endif 362 363 movl %edx, %eax 364 shr $32, %rdx 365 wrmsr 366 .Lend_\@: 367 .endm 368 369 /* 370 * Mitigate Spectre v1 for conditional swapgs code paths. 371 * 372 * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to 373 * prevent a speculative swapgs when coming from kernel space. 374 * 375 * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path, 376 * to prevent the swapgs from getting speculatively skipped when coming from 377 * user space. 378 */ 379 .macro FENCE_SWAPGS_USER_ENTRY 380 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER 381 .endm 382 .macro FENCE_SWAPGS_KERNEL_ENTRY 383 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL 384 .endm 385 386 .macro STACKLEAK_ERASE_NOCLOBBER 387 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 388 PUSH_AND_CLEAR_REGS 389 call stackleak_erase 390 POP_REGS 391 #endif 392 .endm 393 394 #endif /* CONFIG_X86_64 */ 395 396 .macro STACKLEAK_ERASE 397 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 398 call stackleak_erase 399 #endif 400 .endm 401 402 /* 403 * This does 'call enter_from_user_mode' unless we can avoid it based on 404 * kernel config or using the static jump infrastructure. 405 */ 406 .macro CALL_enter_from_user_mode 407 #ifdef CONFIG_CONTEXT_TRACKING 408 #ifdef CONFIG_JUMP_LABEL 409 STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0 410 #endif 411 call enter_from_user_mode 412 .Lafter_call_\@: 413 #endif 414 .endm 415 416 #ifdef CONFIG_PARAVIRT_XXL 417 #define GET_CR2_INTO(reg) GET_CR2_INTO_AX ; _ASM_MOV %_ASM_AX, reg 418 #else 419 #define GET_CR2_INTO(reg) _ASM_MOV %cr2, reg 420 #endif 421