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 10 /* 11 12 x86 function call convention, 64-bit: 13 ------------------------------------- 14 arguments | callee-saved | extra caller-saved | return 15 [callee-clobbered] | | [callee-clobbered] | 16 --------------------------------------------------------------------------- 17 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] 18 19 ( rsp is obviously invariant across normal function calls. (gcc can 'merge' 20 functions when it sees tail-call optimization possibilities) rflags is 21 clobbered. Leftover arguments are passed over the stack frame.) 22 23 [*] In the frame-pointers case rbp is fixed to the stack frame. 24 25 [**] for struct return values wider than 64 bits the return convention is a 26 bit more complex: up to 128 bits width we return small structures 27 straight in rax, rdx. For structures larger than that (3 words or 28 larger) the caller puts a pointer to an on-stack return struct 29 [allocated in the caller's stack frame] into the first argument - i.e. 30 into rdi. All other arguments shift up by one in this case. 31 Fortunately this case is rare in the kernel. 32 33 For 32-bit we have the following conventions - kernel is built with 34 -mregparm=3 and -freg-struct-return: 35 36 x86 function calling convention, 32-bit: 37 ---------------------------------------- 38 arguments | callee-saved | extra caller-saved | return 39 [callee-clobbered] | | [callee-clobbered] | 40 ------------------------------------------------------------------------- 41 eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] 42 43 ( here too esp is obviously invariant across normal function calls. eflags 44 is clobbered. Leftover arguments are passed over the stack frame. ) 45 46 [*] In the frame-pointers case ebp is fixed to the stack frame. 47 48 [**] We build with -freg-struct-return, which on 32-bit means similar 49 semantics as on 64-bit: edx can be used for a second return value 50 (i.e. covering integer and structure sizes up to 64 bits) - after that 51 it gets more complex and more expensive: 3-word or larger struct returns 52 get done in the caller's frame and the pointer to the return struct goes 53 into regparm0, i.e. eax - the other arguments shift up and the 54 function's register parameters degenerate to regparm=2 in essence. 55 56 */ 57 58 #ifdef CONFIG_X86_64 59 60 /* 61 * 64-bit system call stack frame layout defines and helpers, 62 * for assembly code: 63 */ 64 65 /* The layout forms the "struct pt_regs" on the stack: */ 66 /* 67 * C ABI says these regs are callee-preserved. They aren't saved on kernel entry 68 * unless syscall needs a complete, fully filled "struct pt_regs". 69 */ 70 #define R15 0*8 71 #define R14 1*8 72 #define R13 2*8 73 #define R12 3*8 74 #define RBP 4*8 75 #define RBX 5*8 76 /* These regs are callee-clobbered. Always saved on kernel entry. */ 77 #define R11 6*8 78 #define R10 7*8 79 #define R9 8*8 80 #define R8 9*8 81 #define RAX 10*8 82 #define RCX 11*8 83 #define RDX 12*8 84 #define RSI 13*8 85 #define RDI 14*8 86 /* 87 * On syscall entry, this is syscall#. On CPU exception, this is error code. 88 * On hw interrupt, it's IRQ number: 89 */ 90 #define ORIG_RAX 15*8 91 /* Return frame for iretq */ 92 #define RIP 16*8 93 #define CS 17*8 94 #define EFLAGS 18*8 95 #define RSP 19*8 96 #define SS 20*8 97 98 #define SIZEOF_PTREGS 21*8 99 100 .macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0 101 .if \save_ret 102 pushq %rsi /* pt_regs->si */ 103 movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */ 104 movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */ 105 .else 106 pushq %rdi /* pt_regs->di */ 107 pushq %rsi /* pt_regs->si */ 108 .endif 109 pushq \rdx /* pt_regs->dx */ 110 pushq %rcx /* pt_regs->cx */ 111 pushq \rax /* pt_regs->ax */ 112 pushq %r8 /* pt_regs->r8 */ 113 pushq %r9 /* pt_regs->r9 */ 114 pushq %r10 /* pt_regs->r10 */ 115 pushq %r11 /* pt_regs->r11 */ 116 pushq %rbx /* pt_regs->rbx */ 117 pushq %rbp /* pt_regs->rbp */ 118 pushq %r12 /* pt_regs->r12 */ 119 pushq %r13 /* pt_regs->r13 */ 120 pushq %r14 /* pt_regs->r14 */ 121 pushq %r15 /* pt_regs->r15 */ 122 UNWIND_HINT_REGS 123 124 .if \save_ret 125 pushq %rsi /* return address on top of stack */ 126 .endif 127 128 /* 129 * Sanitize registers of values that a speculation attack might 130 * otherwise want to exploit. The lower registers are likely clobbered 131 * well before they could be put to use in a speculative execution 132 * gadget. 133 */ 134 xorl %edx, %edx /* nospec dx */ 135 xorl %ecx, %ecx /* nospec cx */ 136 xorl %r8d, %r8d /* nospec r8 */ 137 xorl %r9d, %r9d /* nospec r9 */ 138 xorl %r10d, %r10d /* nospec r10 */ 139 xorl %r11d, %r11d /* nospec r11 */ 140 xorl %ebx, %ebx /* nospec rbx */ 141 xorl %ebp, %ebp /* nospec rbp */ 142 xorl %r12d, %r12d /* nospec r12 */ 143 xorl %r13d, %r13d /* nospec r13 */ 144 xorl %r14d, %r14d /* nospec r14 */ 145 xorl %r15d, %r15d /* nospec r15 */ 146 147 .endm 148 149 .macro POP_REGS pop_rdi=1 skip_r11rcx=0 150 popq %r15 151 popq %r14 152 popq %r13 153 popq %r12 154 popq %rbp 155 popq %rbx 156 .if \skip_r11rcx 157 popq %rsi 158 .else 159 popq %r11 160 .endif 161 popq %r10 162 popq %r9 163 popq %r8 164 popq %rax 165 .if \skip_r11rcx 166 popq %rsi 167 .else 168 popq %rcx 169 .endif 170 popq %rdx 171 popq %rsi 172 .if \pop_rdi 173 popq %rdi 174 .endif 175 .endm 176 177 #ifdef CONFIG_PAGE_TABLE_ISOLATION 178 179 /* 180 * PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two 181 * halves: 182 */ 183 #define PTI_USER_PGTABLE_BIT PAGE_SHIFT 184 #define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT) 185 #define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT 186 #define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT) 187 #define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK) 188 189 .macro SET_NOFLUSH_BIT reg:req 190 bts $X86_CR3_PCID_NOFLUSH_BIT, \reg 191 .endm 192 193 .macro ADJUST_KERNEL_CR3 reg:req 194 ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID 195 /* Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */ 196 andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg 197 .endm 198 199 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 200 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 201 mov %cr3, \scratch_reg 202 ADJUST_KERNEL_CR3 \scratch_reg 203 mov \scratch_reg, %cr3 204 .Lend_\@: 205 .endm 206 207 #define THIS_CPU_user_pcid_flush_mask \ 208 PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask 209 210 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 211 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 212 mov %cr3, \scratch_reg 213 214 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 215 216 /* 217 * Test if the ASID needs a flush. 218 */ 219 movq \scratch_reg, \scratch_reg2 220 andq $(0x7FF), \scratch_reg /* mask ASID */ 221 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 222 jnc .Lnoflush_\@ 223 224 /* Flush needed, clear the bit */ 225 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 226 movq \scratch_reg2, \scratch_reg 227 jmp .Lwrcr3_pcid_\@ 228 229 .Lnoflush_\@: 230 movq \scratch_reg2, \scratch_reg 231 SET_NOFLUSH_BIT \scratch_reg 232 233 .Lwrcr3_pcid_\@: 234 /* Flip the ASID to the user version */ 235 orq $(PTI_USER_PCID_MASK), \scratch_reg 236 237 .Lwrcr3_\@: 238 /* Flip the PGD to the user version */ 239 orq $(PTI_USER_PGTABLE_MASK), \scratch_reg 240 mov \scratch_reg, %cr3 241 .Lend_\@: 242 .endm 243 244 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 245 pushq %rax 246 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax 247 popq %rax 248 .endm 249 250 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 251 ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI 252 movq %cr3, \scratch_reg 253 movq \scratch_reg, \save_reg 254 /* 255 * Test the user pagetable bit. If set, then the user page tables 256 * are active. If clear CR3 already has the kernel page table 257 * active. 258 */ 259 bt $PTI_USER_PGTABLE_BIT, \scratch_reg 260 jnc .Ldone_\@ 261 262 ADJUST_KERNEL_CR3 \scratch_reg 263 movq \scratch_reg, %cr3 264 265 .Ldone_\@: 266 .endm 267 268 .macro RESTORE_CR3 scratch_reg:req save_reg:req 269 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI 270 271 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID 272 273 /* 274 * KERNEL pages can always resume with NOFLUSH as we do 275 * explicit flushes. 276 */ 277 bt $PTI_USER_PGTABLE_BIT, \save_reg 278 jnc .Lnoflush_\@ 279 280 /* 281 * Check if there's a pending flush for the user ASID we're 282 * about to set. 283 */ 284 movq \save_reg, \scratch_reg 285 andq $(0x7FF), \scratch_reg 286 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask 287 jnc .Lnoflush_\@ 288 289 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask 290 jmp .Lwrcr3_\@ 291 292 .Lnoflush_\@: 293 SET_NOFLUSH_BIT \save_reg 294 295 .Lwrcr3_\@: 296 /* 297 * The CR3 write could be avoided when not changing its value, 298 * but would require a CR3 read *and* a scratch register. 299 */ 300 movq \save_reg, %cr3 301 .Lend_\@: 302 .endm 303 304 #else /* CONFIG_PAGE_TABLE_ISOLATION=n: */ 305 306 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req 307 .endm 308 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req 309 .endm 310 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req 311 .endm 312 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req 313 .endm 314 .macro RESTORE_CR3 scratch_reg:req save_reg:req 315 .endm 316 317 #endif 318 319 /* 320 * Mitigate Spectre v1 for conditional swapgs code paths. 321 * 322 * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to 323 * prevent a speculative swapgs when coming from kernel space. 324 * 325 * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path, 326 * to prevent the swapgs from getting speculatively skipped when coming from 327 * user space. 328 */ 329 .macro FENCE_SWAPGS_USER_ENTRY 330 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER 331 .endm 332 .macro FENCE_SWAPGS_KERNEL_ENTRY 333 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL 334 .endm 335 336 .macro STACKLEAK_ERASE_NOCLOBBER 337 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 338 PUSH_AND_CLEAR_REGS 339 call stackleak_erase 340 POP_REGS 341 #endif 342 .endm 343 344 #else /* CONFIG_X86_64 */ 345 # undef UNWIND_HINT_IRET_REGS 346 # define UNWIND_HINT_IRET_REGS 347 #endif /* !CONFIG_X86_64 */ 348 349 .macro STACKLEAK_ERASE 350 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 351 call stackleak_erase 352 #endif 353 .endm 354