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 ENDBR 54 /* Interrupts are off on entry. */ 55 swapgs 56 57 pushq %rax 58 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 59 popq %rax 60 61 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 62 63 /* Construct struct pt_regs on stack */ 64 pushq $__USER32_DS /* pt_regs->ss */ 65 pushq $0 /* pt_regs->sp = 0 (placeholder) */ 66 67 /* 68 * Push flags. This is nasty. First, interrupts are currently 69 * off, but we need pt_regs->flags to have IF set. Second, if TS 70 * was set in usermode, it's still set, and we're singlestepping 71 * through this code. do_SYSENTER_32() will fix up IF. 72 */ 73 pushfq /* pt_regs->flags (except IF = 0) */ 74 pushq $__USER32_CS /* pt_regs->cs */ 75 pushq $0 /* pt_regs->ip = 0 (placeholder) */ 76SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) 77 78 /* 79 * User tracing code (ptrace or signal handlers) might assume that 80 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 81 * syscall. Just in case the high bits are nonzero, zero-extend 82 * the syscall number. (This could almost certainly be deleted 83 * with no ill effects.) 84 */ 85 movl %eax, %eax 86 87 pushq %rax /* pt_regs->orig_ax */ 88 PUSH_AND_CLEAR_REGS rax=$-ENOSYS 89 UNWIND_HINT_REGS 90 91 cld 92 93 IBRS_ENTER 94 UNTRAIN_RET 95 96 /* 97 * SYSENTER doesn't filter flags, so we need to clear NT and AC 98 * ourselves. To save a few cycles, we can check whether 99 * either was set instead of doing an unconditional popfq. 100 * This needs to happen before enabling interrupts so that 101 * we don't get preempted with NT set. 102 * 103 * If TF is set, we will single-step all the way to here -- do_debug 104 * will ignore all the traps. (Yes, this is slow, but so is 105 * single-stepping in general. This allows us to avoid having 106 * a more complicated code to handle the case where a user program 107 * forces us to single-step through the SYSENTER entry code.) 108 * 109 * NB.: .Lsysenter_fix_flags is a label with the code under it moved 110 * out-of-line as an optimization: NT is unlikely to be set in the 111 * majority of the cases and instead of polluting the I$ unnecessarily, 112 * we're keeping that code behind a branch which will predict as 113 * not-taken and therefore its instructions won't be fetched. 114 */ 115 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp) 116 jnz .Lsysenter_fix_flags 117.Lsysenter_flags_fixed: 118 119 movq %rsp, %rdi 120 call do_SYSENTER_32 121 /* XEN PV guests always use IRET path */ 122 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 123 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 124 jmp sysret32_from_system_call 125 126.Lsysenter_fix_flags: 127 pushq $X86_EFLAGS_FIXED 128 popfq 129 jmp .Lsysenter_flags_fixed 130SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL) 131 ANNOTATE_NOENDBR // is_sysenter_singlestep 132SYM_CODE_END(entry_SYSENTER_compat) 133 134/* 135 * 32-bit SYSCALL entry. 136 * 137 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 138 * on 64-bit kernels running on AMD CPUs. 139 * 140 * The SYSCALL instruction, in principle, should *only* occur in the 141 * vDSO. In practice, it appears that this really is the case. 142 * As evidence: 143 * 144 * - The calling convention for SYSCALL has changed several times without 145 * anyone noticing. 146 * 147 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything 148 * user task that did SYSCALL without immediately reloading SS 149 * would randomly crash. 150 * 151 * - Most programmers do not directly target AMD CPUs, and the 32-bit 152 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD 153 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels 154 * because the SYSCALL instruction in legacy/native 32-bit mode (as 155 * opposed to compat mode) is sufficiently poorly designed as to be 156 * essentially unusable. 157 * 158 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves 159 * RFLAGS to R11, then loads new SS, CS, and RIP from previously 160 * programmed MSRs. RFLAGS gets masked by a value from another MSR 161 * (so CLD and CLAC are not needed). SYSCALL does not save anything on 162 * the stack and does not change RSP. 163 * 164 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode 165 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it). 166 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit 167 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes 168 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors). 169 * 170 * Arguments: 171 * eax system call number 172 * ecx return address 173 * ebx arg1 174 * ebp arg2 (note: not saved in the stack frame, should not be touched) 175 * edx arg3 176 * esi arg4 177 * edi arg5 178 * esp user stack 179 * 0(%esp) arg6 180 */ 181SYM_CODE_START(entry_SYSCALL_compat) 182 UNWIND_HINT_ENTRY 183 ENDBR 184 /* Interrupts are off on entry. */ 185 swapgs 186 187 /* Stash user ESP */ 188 movl %esp, %r8d 189 190 /* Use %rsp as scratch reg. User ESP is stashed in r8 */ 191 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp 192 193 /* Switch to the kernel stack */ 194 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 195 196SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) 197 ANNOTATE_NOENDBR 198 199 /* Construct struct pt_regs on stack */ 200 pushq $__USER32_DS /* pt_regs->ss */ 201 pushq %r8 /* pt_regs->sp */ 202 pushq %r11 /* pt_regs->flags */ 203 pushq $__USER32_CS /* pt_regs->cs */ 204 pushq %rcx /* pt_regs->ip */ 205SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL) 206 movl %eax, %eax /* discard orig_ax high bits */ 207 pushq %rax /* pt_regs->orig_ax */ 208 PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS 209 UNWIND_HINT_REGS 210 211 IBRS_ENTER 212 UNTRAIN_RET 213 214 movq %rsp, %rdi 215 call do_fast_syscall_32 216 /* XEN PV guests always use IRET path */ 217 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 218 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 219 220 /* Opportunistic SYSRET */ 221sysret32_from_system_call: 222 /* 223 * We are not going to return to userspace from the trampoline 224 * stack. So let's erase the thread stack right now. 225 */ 226 STACKLEAK_ERASE 227 228 IBRS_EXIT 229 230 movq RBX(%rsp), %rbx /* pt_regs->rbx */ 231 movq RBP(%rsp), %rbp /* pt_regs->rbp */ 232 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */ 233 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */ 234 addq $RAX, %rsp /* Skip r8-r15 */ 235 popq %rax /* pt_regs->rax */ 236 popq %rdx /* Skip pt_regs->cx */ 237 popq %rdx /* pt_regs->dx */ 238 popq %rsi /* pt_regs->si */ 239 popq %rdi /* pt_regs->di */ 240 241 /* 242 * USERGS_SYSRET32 does: 243 * GSBASE = user's GS base 244 * EIP = ECX 245 * RFLAGS = R11 246 * CS = __USER32_CS 247 * SS = __USER_DS 248 * 249 * ECX will not match pt_regs->cx, but we're returning to a vDSO 250 * trampoline that will fix up RCX, so this is okay. 251 * 252 * R12-R15 are callee-saved, so they contain whatever was in them 253 * when the system call started, which is already known to user 254 * code. We zero R8-R10 to avoid info leaks. 255 */ 256 movq RSP-ORIG_RAX(%rsp), %rsp 257SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL) 258 ANNOTATE_NOENDBR 259 260 /* 261 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored 262 * on the process stack which is not mapped to userspace and 263 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3 264 * switch until after after the last reference to the process 265 * stack. 266 * 267 * %r8/%r9 are zeroed before the sysret, thus safe to clobber. 268 */ 269 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9 270 271 xorl %r8d, %r8d 272 xorl %r9d, %r9d 273 xorl %r10d, %r10d 274 swapgs 275 sysretl 276SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL) 277 ANNOTATE_NOENDBR 278 int3 279SYM_CODE_END(entry_SYSCALL_compat) 280 281/* 282 * 32-bit legacy system call entry. 283 * 284 * 32-bit x86 Linux system calls traditionally used the INT $0x80 285 * instruction. INT $0x80 lands here. 286 * 287 * This entry point can be used by 32-bit and 64-bit programs to perform 288 * 32-bit system calls. Instances of INT $0x80 can be found inline in 289 * various programs and libraries. It is also used by the vDSO's 290 * __kernel_vsyscall fallback for hardware that doesn't support a faster 291 * entry method. Restarted 32-bit system calls also fall back to INT 292 * $0x80 regardless of what instruction was originally used to do the 293 * system call. 294 * 295 * This is considered a slow path. It is not used by most libc 296 * implementations on modern hardware except during process startup. 297 * 298 * Arguments: 299 * eax system call number 300 * ebx arg1 301 * ecx arg2 302 * edx arg3 303 * esi arg4 304 * edi arg5 305 * ebp arg6 306 */ 307SYM_CODE_START(entry_INT80_compat) 308 UNWIND_HINT_ENTRY 309 ENDBR 310 /* 311 * Interrupts are off on entry. 312 */ 313 ASM_CLAC /* Do this early to minimize exposure */ 314 SWAPGS 315 316 /* 317 * User tracing code (ptrace or signal handlers) might assume that 318 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 319 * syscall. Just in case the high bits are nonzero, zero-extend 320 * the syscall number. (This could almost certainly be deleted 321 * with no ill effects.) 322 */ 323 movl %eax, %eax 324 325 /* switch to thread stack expects orig_ax and rdi to be pushed */ 326 pushq %rax /* pt_regs->orig_ax */ 327 328 /* Need to switch before accessing the thread stack. */ 329 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 330 331 /* In the Xen PV case we already run on the thread stack. */ 332 ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV 333 334 movq %rsp, %rax 335 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 336 337 pushq 5*8(%rax) /* regs->ss */ 338 pushq 4*8(%rax) /* regs->rsp */ 339 pushq 3*8(%rax) /* regs->eflags */ 340 pushq 2*8(%rax) /* regs->cs */ 341 pushq 1*8(%rax) /* regs->ip */ 342 pushq 0*8(%rax) /* regs->orig_ax */ 343.Lint80_keep_stack: 344 345 PUSH_AND_CLEAR_REGS rax=$-ENOSYS 346 UNWIND_HINT_REGS 347 348 cld 349 350 IBRS_ENTER 351 UNTRAIN_RET 352 353 movq %rsp, %rdi 354 call do_int80_syscall_32 355 jmp swapgs_restore_regs_and_return_to_usermode 356SYM_CODE_END(entry_INT80_compat) 357