1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * Compatibility mode system call entry point for x86-64. 4 * 5 * Copyright 2000-2002 Andi Kleen, SuSE Labs. 6 */ 7#include <asm/asm-offsets.h> 8#include <asm/current.h> 9#include <asm/errno.h> 10#include <asm/ia32_unistd.h> 11#include <asm/thread_info.h> 12#include <asm/segment.h> 13#include <asm/irqflags.h> 14#include <asm/asm.h> 15#include <asm/smap.h> 16#include <asm/nospec-branch.h> 17#include <linux/linkage.h> 18#include <linux/err.h> 19 20#include "calling.h" 21 22 .section .entry.text, "ax" 23 24/* 25 * 32-bit SYSENTER entry. 26 * 27 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 28 * on 64-bit kernels running on Intel CPUs. 29 * 30 * The SYSENTER instruction, in principle, should *only* occur in the 31 * vDSO. In practice, a small number of Android devices were shipped 32 * with a copy of Bionic that inlined a SYSENTER instruction. This 33 * never happened in any of Google's Bionic versions -- it only happened 34 * in a narrow range of Intel-provided versions. 35 * 36 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs. 37 * IF and VM in RFLAGS are cleared (IOW: interrupts are off). 38 * SYSENTER does not save anything on the stack, 39 * and does not save old RIP (!!!), RSP, or RFLAGS. 40 * 41 * Arguments: 42 * eax system call number 43 * ebx arg1 44 * ecx arg2 45 * edx arg3 46 * esi arg4 47 * edi arg5 48 * ebp user stack 49 * 0(%ebp) arg6 50 */ 51SYM_CODE_START(entry_SYSENTER_compat) 52 UNWIND_HINT_ENTRY 53 /* Interrupts are off on entry. */ 54 SWAPGS 55 56 pushq %rax 57 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 58 popq %rax 59 60 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 61 62 /* Construct struct pt_regs on stack */ 63 pushq $__USER32_DS /* pt_regs->ss */ 64 pushq $0 /* pt_regs->sp = 0 (placeholder) */ 65 66 /* 67 * Push flags. This is nasty. First, interrupts are currently 68 * off, but we need pt_regs->flags to have IF set. Second, if TS 69 * was set in usermode, it's still set, and we're singlestepping 70 * through this code. do_SYSENTER_32() will fix up IF. 71 */ 72 pushfq /* pt_regs->flags (except IF = 0) */ 73 pushq $__USER32_CS /* pt_regs->cs */ 74 pushq $0 /* pt_regs->ip = 0 (placeholder) */ 75SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) 76 77 /* 78 * User tracing code (ptrace or signal handlers) might assume that 79 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 80 * syscall. Just in case the high bits are nonzero, zero-extend 81 * the syscall number. (This could almost certainly be deleted 82 * with no ill effects.) 83 */ 84 movl %eax, %eax 85 86 pushq %rax /* pt_regs->orig_ax */ 87 pushq %rdi /* pt_regs->di */ 88 pushq %rsi /* pt_regs->si */ 89 pushq %rdx /* pt_regs->dx */ 90 pushq %rcx /* pt_regs->cx */ 91 pushq $-ENOSYS /* pt_regs->ax */ 92 pushq $0 /* pt_regs->r8 = 0 */ 93 xorl %r8d, %r8d /* nospec r8 */ 94 pushq $0 /* pt_regs->r9 = 0 */ 95 xorl %r9d, %r9d /* nospec r9 */ 96 pushq $0 /* pt_regs->r10 = 0 */ 97 xorl %r10d, %r10d /* nospec r10 */ 98 pushq $0 /* pt_regs->r11 = 0 */ 99 xorl %r11d, %r11d /* nospec r11 */ 100 pushq %rbx /* pt_regs->rbx */ 101 xorl %ebx, %ebx /* nospec rbx */ 102 pushq %rbp /* pt_regs->rbp (will be overwritten) */ 103 xorl %ebp, %ebp /* nospec rbp */ 104 pushq $0 /* pt_regs->r12 = 0 */ 105 xorl %r12d, %r12d /* nospec r12 */ 106 pushq $0 /* pt_regs->r13 = 0 */ 107 xorl %r13d, %r13d /* nospec r13 */ 108 pushq $0 /* pt_regs->r14 = 0 */ 109 xorl %r14d, %r14d /* nospec r14 */ 110 pushq $0 /* pt_regs->r15 = 0 */ 111 xorl %r15d, %r15d /* nospec r15 */ 112 113 UNWIND_HINT_REGS 114 115 cld 116 117 IBRS_ENTER 118 UNTRAIN_RET 119 120 /* 121 * SYSENTER doesn't filter flags, so we need to clear NT and AC 122 * ourselves. To save a few cycles, we can check whether 123 * either was set instead of doing an unconditional popfq. 124 * This needs to happen before enabling interrupts so that 125 * we don't get preempted with NT set. 126 * 127 * If TF is set, we will single-step all the way to here -- do_debug 128 * will ignore all the traps. (Yes, this is slow, but so is 129 * single-stepping in general. This allows us to avoid having 130 * a more complicated code to handle the case where a user program 131 * forces us to single-step through the SYSENTER entry code.) 132 * 133 * NB.: .Lsysenter_fix_flags is a label with the code under it moved 134 * out-of-line as an optimization: NT is unlikely to be set in the 135 * majority of the cases and instead of polluting the I$ unnecessarily, 136 * we're keeping that code behind a branch which will predict as 137 * not-taken and therefore its instructions won't be fetched. 138 */ 139 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp) 140 jnz .Lsysenter_fix_flags 141.Lsysenter_flags_fixed: 142 143 movq %rsp, %rdi 144 call do_SYSENTER_32 145 /* XEN PV guests always use IRET path */ 146 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 147 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 148 jmp sysret32_from_system_call 149 150.Lsysenter_fix_flags: 151 pushq $X86_EFLAGS_FIXED 152 popfq 153 jmp .Lsysenter_flags_fixed 154SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL) 155SYM_CODE_END(entry_SYSENTER_compat) 156 157/* 158 * 32-bit SYSCALL entry. 159 * 160 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 161 * on 64-bit kernels running on AMD CPUs. 162 * 163 * The SYSCALL instruction, in principle, should *only* occur in the 164 * vDSO. In practice, it appears that this really is the case. 165 * As evidence: 166 * 167 * - The calling convention for SYSCALL has changed several times without 168 * anyone noticing. 169 * 170 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything 171 * user task that did SYSCALL without immediately reloading SS 172 * would randomly crash. 173 * 174 * - Most programmers do not directly target AMD CPUs, and the 32-bit 175 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD 176 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels 177 * because the SYSCALL instruction in legacy/native 32-bit mode (as 178 * opposed to compat mode) is sufficiently poorly designed as to be 179 * essentially unusable. 180 * 181 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves 182 * RFLAGS to R11, then loads new SS, CS, and RIP from previously 183 * programmed MSRs. RFLAGS gets masked by a value from another MSR 184 * (so CLD and CLAC are not needed). SYSCALL does not save anything on 185 * the stack and does not change RSP. 186 * 187 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode 188 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it). 189 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit 190 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes 191 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors). 192 * 193 * Arguments: 194 * eax system call number 195 * ecx return address 196 * ebx arg1 197 * ebp arg2 (note: not saved in the stack frame, should not be touched) 198 * edx arg3 199 * esi arg4 200 * edi arg5 201 * esp user stack 202 * 0(%esp) arg6 203 */ 204SYM_CODE_START(entry_SYSCALL_compat) 205 UNWIND_HINT_ENTRY 206 /* Interrupts are off on entry. */ 207 swapgs 208 209 /* Stash user ESP */ 210 movl %esp, %r8d 211 212 /* Use %rsp as scratch reg. User ESP is stashed in r8 */ 213 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp 214 215 /* Switch to the kernel stack */ 216 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 217 218SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) 219 220 /* Construct struct pt_regs on stack */ 221 pushq $__USER32_DS /* pt_regs->ss */ 222 pushq %r8 /* pt_regs->sp */ 223 pushq %r11 /* pt_regs->flags */ 224 pushq $__USER32_CS /* pt_regs->cs */ 225 pushq %rcx /* pt_regs->ip */ 226SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL) 227 movl %eax, %eax /* discard orig_ax high bits */ 228 pushq %rax /* pt_regs->orig_ax */ 229 pushq %rdi /* pt_regs->di */ 230 pushq %rsi /* pt_regs->si */ 231 xorl %esi, %esi /* nospec si */ 232 pushq %rdx /* pt_regs->dx */ 233 xorl %edx, %edx /* nospec dx */ 234 pushq %rbp /* pt_regs->cx (stashed in bp) */ 235 xorl %ecx, %ecx /* nospec cx */ 236 pushq $-ENOSYS /* pt_regs->ax */ 237 pushq $0 /* pt_regs->r8 = 0 */ 238 xorl %r8d, %r8d /* nospec r8 */ 239 pushq $0 /* pt_regs->r9 = 0 */ 240 xorl %r9d, %r9d /* nospec r9 */ 241 pushq $0 /* pt_regs->r10 = 0 */ 242 xorl %r10d, %r10d /* nospec r10 */ 243 pushq $0 /* pt_regs->r11 = 0 */ 244 xorl %r11d, %r11d /* nospec r11 */ 245 pushq %rbx /* pt_regs->rbx */ 246 xorl %ebx, %ebx /* nospec rbx */ 247 pushq %rbp /* pt_regs->rbp (will be overwritten) */ 248 xorl %ebp, %ebp /* nospec rbp */ 249 pushq $0 /* pt_regs->r12 = 0 */ 250 xorl %r12d, %r12d /* nospec r12 */ 251 pushq $0 /* pt_regs->r13 = 0 */ 252 xorl %r13d, %r13d /* nospec r13 */ 253 pushq $0 /* pt_regs->r14 = 0 */ 254 xorl %r14d, %r14d /* nospec r14 */ 255 pushq $0 /* pt_regs->r15 = 0 */ 256 xorl %r15d, %r15d /* nospec r15 */ 257 258 UNWIND_HINT_REGS 259 260 IBRS_ENTER 261 UNTRAIN_RET 262 263 movq %rsp, %rdi 264 call do_fast_syscall_32 265 /* XEN PV guests always use IRET path */ 266 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 267 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 268 269 /* Opportunistic SYSRET */ 270sysret32_from_system_call: 271 /* 272 * We are not going to return to userspace from the trampoline 273 * stack. So let's erase the thread stack right now. 274 */ 275 STACKLEAK_ERASE 276 277 IBRS_EXIT 278 279 movq RBX(%rsp), %rbx /* pt_regs->rbx */ 280 movq RBP(%rsp), %rbp /* pt_regs->rbp */ 281 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */ 282 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */ 283 addq $RAX, %rsp /* Skip r8-r15 */ 284 popq %rax /* pt_regs->rax */ 285 popq %rdx /* Skip pt_regs->cx */ 286 popq %rdx /* pt_regs->dx */ 287 popq %rsi /* pt_regs->si */ 288 popq %rdi /* pt_regs->di */ 289 290 /* 291 * USERGS_SYSRET32 does: 292 * GSBASE = user's GS base 293 * EIP = ECX 294 * RFLAGS = R11 295 * CS = __USER32_CS 296 * SS = __USER_DS 297 * 298 * ECX will not match pt_regs->cx, but we're returning to a vDSO 299 * trampoline that will fix up RCX, so this is okay. 300 * 301 * R12-R15 are callee-saved, so they contain whatever was in them 302 * when the system call started, which is already known to user 303 * code. We zero R8-R10 to avoid info leaks. 304 */ 305 movq RSP-ORIG_RAX(%rsp), %rsp 306 307 /* 308 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored 309 * on the process stack which is not mapped to userspace and 310 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3 311 * switch until after after the last reference to the process 312 * stack. 313 * 314 * %r8/%r9 are zeroed before the sysret, thus safe to clobber. 315 */ 316 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9 317 318 xorl %r8d, %r8d 319 xorl %r9d, %r9d 320 xorl %r10d, %r10d 321 swapgs 322 sysretl 323SYM_CODE_END(entry_SYSCALL_compat) 324 325/* 326 * 32-bit legacy system call entry. 327 * 328 * 32-bit x86 Linux system calls traditionally used the INT $0x80 329 * instruction. INT $0x80 lands here. 330 * 331 * This entry point can be used by 32-bit and 64-bit programs to perform 332 * 32-bit system calls. Instances of INT $0x80 can be found inline in 333 * various programs and libraries. It is also used by the vDSO's 334 * __kernel_vsyscall fallback for hardware that doesn't support a faster 335 * entry method. Restarted 32-bit system calls also fall back to INT 336 * $0x80 regardless of what instruction was originally used to do the 337 * system call. 338 * 339 * This is considered a slow path. It is not used by most libc 340 * implementations on modern hardware except during process startup. 341 * 342 * Arguments: 343 * eax system call number 344 * ebx arg1 345 * ecx arg2 346 * edx arg3 347 * esi arg4 348 * edi arg5 349 * ebp arg6 350 */ 351SYM_CODE_START(entry_INT80_compat) 352 UNWIND_HINT_ENTRY 353 /* 354 * Interrupts are off on entry. 355 */ 356 ASM_CLAC /* Do this early to minimize exposure */ 357 SWAPGS 358 359 /* 360 * User tracing code (ptrace or signal handlers) might assume that 361 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 362 * syscall. Just in case the high bits are nonzero, zero-extend 363 * the syscall number. (This could almost certainly be deleted 364 * with no ill effects.) 365 */ 366 movl %eax, %eax 367 368 /* switch to thread stack expects orig_ax and rdi to be pushed */ 369 pushq %rax /* pt_regs->orig_ax */ 370 pushq %rdi /* pt_regs->di */ 371 372 /* Need to switch before accessing the thread stack. */ 373 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi 374 375 /* In the Xen PV case we already run on the thread stack. */ 376 ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV 377 378 movq %rsp, %rdi 379 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 380 381 pushq 6*8(%rdi) /* regs->ss */ 382 pushq 5*8(%rdi) /* regs->rsp */ 383 pushq 4*8(%rdi) /* regs->eflags */ 384 pushq 3*8(%rdi) /* regs->cs */ 385 pushq 2*8(%rdi) /* regs->ip */ 386 pushq 1*8(%rdi) /* regs->orig_ax */ 387 pushq (%rdi) /* pt_regs->di */ 388.Lint80_keep_stack: 389 390 pushq %rsi /* pt_regs->si */ 391 xorl %esi, %esi /* nospec si */ 392 pushq %rdx /* pt_regs->dx */ 393 xorl %edx, %edx /* nospec dx */ 394 pushq %rcx /* pt_regs->cx */ 395 xorl %ecx, %ecx /* nospec cx */ 396 pushq $-ENOSYS /* pt_regs->ax */ 397 pushq %r8 /* pt_regs->r8 */ 398 xorl %r8d, %r8d /* nospec r8 */ 399 pushq %r9 /* pt_regs->r9 */ 400 xorl %r9d, %r9d /* nospec r9 */ 401 pushq %r10 /* pt_regs->r10*/ 402 xorl %r10d, %r10d /* nospec r10 */ 403 pushq %r11 /* pt_regs->r11 */ 404 xorl %r11d, %r11d /* nospec r11 */ 405 pushq %rbx /* pt_regs->rbx */ 406 xorl %ebx, %ebx /* nospec rbx */ 407 pushq %rbp /* pt_regs->rbp */ 408 xorl %ebp, %ebp /* nospec rbp */ 409 pushq %r12 /* pt_regs->r12 */ 410 xorl %r12d, %r12d /* nospec r12 */ 411 pushq %r13 /* pt_regs->r13 */ 412 xorl %r13d, %r13d /* nospec r13 */ 413 pushq %r14 /* pt_regs->r14 */ 414 xorl %r14d, %r14d /* nospec r14 */ 415 pushq %r15 /* pt_regs->r15 */ 416 xorl %r15d, %r15d /* nospec r15 */ 417 418 UNWIND_HINT_REGS 419 420 cld 421 422 IBRS_ENTER 423 UNTRAIN_RET 424 425 movq %rsp, %rdi 426 call do_int80_syscall_32 427 jmp swapgs_restore_regs_and_return_to_usermode 428SYM_CODE_END(entry_INT80_compat) 429