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/ptrace-abi.h> 10 #include <asm/msr.h> 11 #include <asm/nospec-branch.h> 12 13 /* 14 15 x86 function call convention, 64-bit: 16 ------------------------------------- 17 arguments | callee-saved | extra caller-saved | return 18 [callee-clobbered] | | [callee-clobbered] | 19 --------------------------------------------------------------------------- 20 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] 21 22 ( rsp is obviously invariant across normal function calls. (gcc can 'merge' 23 functions when it sees tail-call optimization possibilities) rflags is 24 clobbered. Leftover arguments are passed over the stack frame.) 25 26 [*] In the frame-pointers case rbp is fixed to the stack frame. 27 28 [**] for struct return values wider than 64 bits the return convention is a 29 bit more complex: up to 128 bits width we return small structures 30 straight in rax, rdx. For structures larger than that (3 words or 31 larger) the caller puts a pointer to an on-stack return struct 32 [allocated in the caller's stack frame] into the first argument - i.e. 33 into rdi. All other arguments shift up by one in this case. 34 Fortunately this case is rare in the kernel. 35 36 For 32-bit we have the following conventions - kernel is built with 37 -mregparm=3 and -freg-struct-return: 38 39 x86 function calling convention, 32-bit: 40 ---------------------------------------- 41 arguments | callee-saved | extra caller-saved | return 42 [callee-clobbered] | | [callee-clobbered] | 43 ------------------------------------------------------------------------- 44 eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] 45 46 ( here too esp is obviously invariant across normal function calls. eflags 47 is clobbered. Leftover arguments are passed over the stack frame. ) 48 49 [*] In the frame-pointers case ebp is fixed to the stack frame. 50 51 [**] We build with -freg-struct-return, which on 32-bit means similar 52 semantics as on 64-bit: edx can be used for a second return value 53 (i.e. covering integer and structure sizes up to 64 bits) - after that 54 it gets more complex and more expensive: 3-word or larger struct returns 55 get done in the caller's frame and the pointer to the return struct goes 56 into regparm0, i.e. eax - the other arguments shift up and the 57 function's register parameters degenerate to regparm=2 in essence. 58 59 */ 60 61 #ifdef CONFIG_X86_64 62 63 /* 64 * 64-bit system call stack frame layout defines and helpers, 65 * for assembly code: 66 */ 67 68 .macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 69 .if \save_ret 70 pushq %rsi /* pt_regs->si */ 71 movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */ 72 movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */ 73 .else 74 pushq %rdi /* pt_regs->di */ 75 pushq %rsi /* pt_regs->si */ 76 .endif 77 pushq \rdx /* pt_regs->dx */ 78 pushq \rcx /* pt_regs->cx */ 79 pushq \rax /* pt_regs->ax */ 80 pushq %r8 /* pt_regs->r8 */ 81 pushq %r9 /* pt_regs->r9 */ 82 pushq %r10 /* pt_regs->r10 */ 83 pushq %r11 /* pt_regs->r11 */ 84 pushq %rbx /* pt_regs->rbx */ 85 pushq %rbp /* pt_regs->rbp */ 86 pushq %r12 /* pt_regs->r12 */ 87 pushq %r13 /* pt_regs->r13 */ 88 pushq %r14 /* pt_regs->r14 */ 89 pushq %r15 /* pt_regs->r15 */ 90 UNWIND_HINT_REGS 91 92 .if \save_ret 93 pushq %rsi /* return address on top of stack */ 94 .endif 95 .endm 96 97 .macro CLEAR_REGS 98 /* 99 * Sanitize registers of values that a speculation attack might 100 * otherwise want to exploit. The lower registers are likely clobbered 101 * well before they could be put to use in a speculative execution 102 * gadget. 103 */ 104 xorl %esi, %esi /* nospec si */ 105 xorl %edx, %edx /* nospec dx */ 106 xorl %ecx, %ecx /* nospec cx */ 107 xorl %r8d, %r8d /* nospec r8 */ 108 xorl %r9d, %r9d /* nospec r9 */ 109 xorl %r10d, %r10d /* nospec r10 */ 110 xorl %r11d, %r11d /* nospec r11 */ 111 xorl %ebx, %ebx /* nospec rbx */ 112 xorl %ebp, %ebp /* nospec rbp */ 113 xorl %r12d, %r12d /* nospec r12 */ 114 xorl %r13d, %r13d /* nospec r13 */ 115 xorl %r14d, %r14d /* nospec r14 */ 116 xorl %r15d, %r15d /* nospec r15 */ 117 118 .endm 119 120 .macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 121 PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret 122 CLEAR_REGS 123 .endm 124 125 .macro POP_REGS pop_rdi=1 126 popq %r15 127 popq %r14 128 popq %r13 129 popq %r12 130 popq %rbp 131 popq %rbx 132 popq %r11 133 popq %r10 134 popq %r9 135 popq %r8 136 popq %rax 137 popq %rcx 138 popq %rdx 139 popq %rsi 140 .if \pop_rdi 141 popq %rdi 142 .endif 143 .endm 144 145 #ifdef CONFIG_PAGE_TABLE_ISOLATION 146 147 /* 148 * PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two 149 * halves: 150 */ 151 #define PTI_USER_PGTABLE_BIT PAGE_SHIFT 152 #define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT) 153 #define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT 154 #define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT) 155 #define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK) 156 157 .macro SET_NOFLUSH_BIT reg:req 158 bts $X86_CR3_PCID_NOFLUSH_BIT, \reg 159 .endm 160 161 .macro ADJUST_KERNEL_CR3 reg:req 162 ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID 163 /* Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */ 164 andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg 165 .endm 166 167 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 168 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 169 mov %cr3, \scratch_reg 170 ADJUST_KERNEL_CR3 \scratch_reg 171 mov \scratch_reg, %cr3 172 .Lend_\@: 173 .endm 174 175 #define THIS_CPU_user_pcid_flush_mask \ 176 PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask 177 178 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 179 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 180 mov %cr3, \scratch_reg 181 182 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 183 184 /* 185 * Test if the ASID needs a flush. 186 */ 187 movq \scratch_reg, \scratch_reg2 188 andq $(0x7FF), \scratch_reg /* mask ASID */ 189 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 190 jnc .Lnoflush_\@ 191 192 /* Flush needed, clear the bit */ 193 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 194 movq \scratch_reg2, \scratch_reg 195 jmp .Lwrcr3_pcid_\@ 196 197 .Lnoflush_\@: 198 movq \scratch_reg2, \scratch_reg 199 SET_NOFLUSH_BIT \scratch_reg 200 201 .Lwrcr3_pcid_\@: 202 /* Flip the ASID to the user version */ 203 orq $(PTI_USER_PCID_MASK), \scratch_reg 204 205 .Lwrcr3_\@: 206 /* Flip the PGD to the user version */ 207 orq $(PTI_USER_PGTABLE_MASK), \scratch_reg 208 mov \scratch_reg, %cr3 209 .Lend_\@: 210 .endm 211 212 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 213 pushq %rax 214 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax 215 popq %rax 216 .endm 217 218 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 219 ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI 220 movq %cr3, \scratch_reg 221 movq \scratch_reg, \save_reg 222 /* 223 * Test the user pagetable bit. If set, then the user page tables 224 * are active. If clear CR3 already has the kernel page table 225 * active. 226 */ 227 bt $PTI_USER_PGTABLE_BIT, \scratch_reg 228 jnc .Ldone_\@ 229 230 ADJUST_KERNEL_CR3 \scratch_reg 231 movq \scratch_reg, %cr3 232 233 .Ldone_\@: 234 .endm 235 236 .macro RESTORE_CR3 scratch_reg:req save_reg:req 237 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 238 239 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 240 241 /* 242 * KERNEL pages can always resume with NOFLUSH as we do 243 * explicit flushes. 244 */ 245 bt $PTI_USER_PGTABLE_BIT, \save_reg 246 jnc .Lnoflush_\@ 247 248 /* 249 * Check if there's a pending flush for the user ASID we're 250 * about to set. 251 */ 252 movq \save_reg, \scratch_reg 253 andq $(0x7FF), \scratch_reg 254 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 255 jnc .Lnoflush_\@ 256 257 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 258 jmp .Lwrcr3_\@ 259 260 .Lnoflush_\@: 261 SET_NOFLUSH_BIT \save_reg 262 263 .Lwrcr3_\@: 264 /* 265 * The CR3 write could be avoided when not changing its value, 266 * but would require a CR3 read *and* a scratch register. 267 */ 268 movq \save_reg, %cr3 269 .Lend_\@: 270 .endm 271 272 #else /* CONFIG_PAGE_TABLE_ISOLATION=n: */ 273 274 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 275 .endm 276 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 277 .endm 278 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 279 .endm 280 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 281 .endm 282 .macro RESTORE_CR3 scratch_reg:req save_reg:req 283 .endm 284 285 #endif 286 287 /* 288 * IBRS kernel mitigation for Spectre_v2. 289 * 290 * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers 291 * the regs it uses (AX, CX, DX). Must be called before the first RET 292 * instruction (NOTE! UNTRAIN_RET includes a RET instruction) 293 * 294 * The optional argument is used to save/restore the current value, 295 * which is used on the paranoid paths. 296 * 297 * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set. 298 */ 299 .macro IBRS_ENTER save_reg 300 #ifdef CONFIG_CPU_IBRS_ENTRY 301 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS 302 movl $MSR_IA32_SPEC_CTRL, %ecx 303 304 .ifnb \save_reg 305 rdmsr 306 shl $32, %rdx 307 or %rdx, %rax 308 mov %rax, \save_reg 309 test $SPEC_CTRL_IBRS, %eax 310 jz .Ldo_wrmsr_\@ 311 lfence 312 jmp .Lend_\@ 313 .Ldo_wrmsr_\@: 314 .endif 315 316 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx 317 movl %edx, %eax 318 shr $32, %rdx 319 wrmsr 320 .Lend_\@: 321 #endif 322 .endm 323 324 /* 325 * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX) 326 * regs. Must be called after the last RET. 327 */ 328 .macro IBRS_EXIT save_reg 329 #ifdef CONFIG_CPU_IBRS_ENTRY 330 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS 331 movl $MSR_IA32_SPEC_CTRL, %ecx 332 333 .ifnb \save_reg 334 mov \save_reg, %rdx 335 .else 336 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx 337 andl $(~SPEC_CTRL_IBRS), %edx 338 .endif 339 340 movl %edx, %eax 341 shr $32, %rdx 342 wrmsr 343 .Lend_\@: 344 #endif 345 .endm 346 347 /* 348 * Mitigate Spectre v1 for conditional swapgs code paths. 349 * 350 * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to 351 * prevent a speculative swapgs when coming from kernel space. 352 * 353 * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path, 354 * to prevent the swapgs from getting speculatively skipped when coming from 355 * user space. 356 */ 357 .macro FENCE_SWAPGS_USER_ENTRY 358 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER 359 .endm 360 .macro FENCE_SWAPGS_KERNEL_ENTRY 361 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL 362 .endm 363 364 .macro STACKLEAK_ERASE_NOCLOBBER 365 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 366 PUSH_AND_CLEAR_REGS 367 call stackleak_erase 368 POP_REGS 369 #endif 370 .endm 371 372 .macro SAVE_AND_SET_GSBASE scratch_reg:req save_reg:req 373 rdgsbase \save_reg 374 GET_PERCPU_BASE \scratch_reg 375 wrgsbase \scratch_reg 376 .endm 377 378 #else /* CONFIG_X86_64 */ 379 # undef UNWIND_HINT_IRET_REGS 380 # define UNWIND_HINT_IRET_REGS 381 #endif /* !CONFIG_X86_64 */ 382 383 .macro STACKLEAK_ERASE 384 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 385 call stackleak_erase 386 #endif 387 .endm 388 389 #ifdef CONFIG_SMP 390 391 /* 392 * CPU/node NR is loaded from the limit (size) field of a special segment 393 * descriptor entry in GDT. 394 */ 395 .macro LOAD_CPU_AND_NODE_SEG_LIMIT reg:req 396 movq $__CPUNODE_SEG, \reg 397 lsl \reg, \reg 398 .endm 399 400 /* 401 * Fetch the per-CPU GSBASE value for this processor and put it in @reg. 402 * We normally use %gs for accessing per-CPU data, but we are setting up 403 * %gs here and obviously can not use %gs itself to access per-CPU data. 404 * 405 * Do not use RDPID, because KVM loads guest's TSC_AUX on vm-entry and 406 * may not restore the host's value until the CPU returns to userspace. 407 * Thus the kernel would consume a guest's TSC_AUX if an NMI arrives 408 * while running KVM's run loop. 409 */ 410 .macro GET_PERCPU_BASE reg:req 411 LOAD_CPU_AND_NODE_SEG_LIMIT \reg 412 andq $VDSO_CPUNODE_MASK, \reg 413 movq __per_cpu_offset(, \reg, 8), \reg 414 .endm 415 416 #else 417 418 .macro GET_PERCPU_BASE reg:req 419 movq pcpu_unit_offsets(%rip), \reg 420 .endm 421 422 #endif /* CONFIG_SMP */ 423
