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(pcpu_hot + X86_top_of_stack), %rsp 62 63 /* Construct struct pt_regs on stack */ 64 pushq $__USER_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 /* 94 * SYSENTER doesn't filter flags, so we need to clear NT and AC 95 * ourselves. To save a few cycles, we can check whether 96 * either was set instead of doing an unconditional popfq. 97 * This needs to happen before enabling interrupts so that 98 * we don't get preempted with NT set. 99 * 100 * If TF is set, we will single-step all the way to here -- do_debug 101 * will ignore all the traps. (Yes, this is slow, but so is 102 * single-stepping in general. This allows us to avoid having 103 * a more complicated code to handle the case where a user program 104 * forces us to single-step through the SYSENTER entry code.) 105 * 106 * NB.: .Lsysenter_fix_flags is a label with the code under it moved 107 * out-of-line as an optimization: NT is unlikely to be set in the 108 * majority of the cases and instead of polluting the I$ unnecessarily, 109 * we're keeping that code behind a branch which will predict as 110 * not-taken and therefore its instructions won't be fetched. 111 */ 112 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp) 113 jnz .Lsysenter_fix_flags 114.Lsysenter_flags_fixed: 115 116 /* 117 * CPU bugs mitigations mechanisms can call other functions. They 118 * should be invoked after making sure TF is cleared because 119 * single-step is ignored only for instructions inside the 120 * entry_SYSENTER_compat function. 121 */ 122 IBRS_ENTER 123 UNTRAIN_RET 124 CLEAR_BRANCH_HISTORY 125 126 movq %rsp, %rdi 127 call do_SYSENTER_32 128 /* XEN PV guests always use IRET path */ 129 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 130 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 131 jmp sysret32_from_system_call 132 133.Lsysenter_fix_flags: 134 pushq $X86_EFLAGS_FIXED 135 popfq 136 jmp .Lsysenter_flags_fixed 137SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL) 138SYM_CODE_END(entry_SYSENTER_compat) 139 140/* 141 * 32-bit SYSCALL entry. 142 * 143 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 144 * on 64-bit kernels running on AMD CPUs. 145 * 146 * The SYSCALL instruction, in principle, should *only* occur in the 147 * vDSO. In practice, it appears that this really is the case. 148 * As evidence: 149 * 150 * - The calling convention for SYSCALL has changed several times without 151 * anyone noticing. 152 * 153 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything 154 * user task that did SYSCALL without immediately reloading SS 155 * would randomly crash. 156 * 157 * - Most programmers do not directly target AMD CPUs, and the 32-bit 158 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD 159 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels 160 * because the SYSCALL instruction in legacy/native 32-bit mode (as 161 * opposed to compat mode) is sufficiently poorly designed as to be 162 * essentially unusable. 163 * 164 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves 165 * RFLAGS to R11, then loads new SS, CS, and RIP from previously 166 * programmed MSRs. RFLAGS gets masked by a value from another MSR 167 * (so CLD and CLAC are not needed). SYSCALL does not save anything on 168 * the stack and does not change RSP. 169 * 170 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode 171 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it). 172 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit 173 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes 174 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors). 175 * 176 * Arguments: 177 * eax system call number 178 * ecx return address 179 * ebx arg1 180 * ebp arg2 (note: not saved in the stack frame, should not be touched) 181 * edx arg3 182 * esi arg4 183 * edi arg5 184 * esp user stack 185 * 0(%esp) arg6 186 */ 187SYM_CODE_START(entry_SYSCALL_compat) 188 UNWIND_HINT_ENTRY 189 ENDBR 190 /* Interrupts are off on entry. */ 191 swapgs 192 193 /* Stash user ESP */ 194 movl %esp, %r8d 195 196 /* Use %rsp as scratch reg. User ESP is stashed in r8 */ 197 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp 198 199 /* Switch to the kernel stack */ 200 movq PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp 201 202SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) 203 ANNOTATE_NOENDBR 204 205 /* Construct struct pt_regs on stack */ 206 pushq $__USER_DS /* pt_regs->ss */ 207 pushq %r8 /* pt_regs->sp */ 208 pushq %r11 /* pt_regs->flags */ 209 pushq $__USER32_CS /* pt_regs->cs */ 210 pushq %rcx /* pt_regs->ip */ 211SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL) 212 movl %eax, %eax /* discard orig_ax high bits */ 213 pushq %rax /* pt_regs->orig_ax */ 214 PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS 215 UNWIND_HINT_REGS 216 217 IBRS_ENTER 218 UNTRAIN_RET 219 CLEAR_BRANCH_HISTORY 220 221 movq %rsp, %rdi 222 call do_fast_syscall_32 223 /* XEN PV guests always use IRET path */ 224 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 225 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 226 227 /* Opportunistic SYSRET */ 228sysret32_from_system_call: 229 /* 230 * We are not going to return to userspace from the trampoline 231 * stack. So let's erase the thread stack right now. 232 */ 233 STACKLEAK_ERASE 234 235 IBRS_EXIT 236 237 movq RBX(%rsp), %rbx /* pt_regs->rbx */ 238 movq RBP(%rsp), %rbp /* pt_regs->rbp */ 239 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */ 240 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */ 241 addq $RAX, %rsp /* Skip r8-r15 */ 242 popq %rax /* pt_regs->rax */ 243 popq %rdx /* Skip pt_regs->cx */ 244 popq %rdx /* pt_regs->dx */ 245 popq %rsi /* pt_regs->si */ 246 popq %rdi /* pt_regs->di */ 247 248 /* 249 * USERGS_SYSRET32 does: 250 * GSBASE = user's GS base 251 * EIP = ECX 252 * RFLAGS = R11 253 * CS = __USER32_CS 254 * SS = __USER_DS 255 * 256 * ECX will not match pt_regs->cx, but we're returning to a vDSO 257 * trampoline that will fix up RCX, so this is okay. 258 * 259 * R12-R15 are callee-saved, so they contain whatever was in them 260 * when the system call started, which is already known to user 261 * code. We zero R8-R10 to avoid info leaks. 262 */ 263 movq RSP-ORIG_RAX(%rsp), %rsp 264SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL) 265 ANNOTATE_NOENDBR 266 267 /* 268 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored 269 * on the process stack which is not mapped to userspace and 270 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3 271 * switch until after after the last reference to the process 272 * stack. 273 * 274 * %r8/%r9 are zeroed before the sysret, thus safe to clobber. 275 */ 276 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9 277 278 xorl %r8d, %r8d 279 xorl %r9d, %r9d 280 xorl %r10d, %r10d 281 swapgs 282 CLEAR_CPU_BUFFERS 283 sysretl 284SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL) 285 ANNOTATE_NOENDBR 286 int3 287SYM_CODE_END(entry_SYSCALL_compat) 288 289/* 290 * int 0x80 is used by 32 bit mode as a system call entry. Normally idt entries 291 * point to C routines, however since this is a system call interface the branch 292 * history needs to be scrubbed to protect against BHI attacks, and that 293 * scrubbing needs to take place in assembly code prior to entering any C 294 * routines. 295 */ 296SYM_CODE_START(int80_emulation) 297 ANNOTATE_NOENDBR 298 UNWIND_HINT_FUNC 299 CLEAR_BRANCH_HISTORY 300 jmp do_int80_emulation 301SYM_CODE_END(int80_emulation) 302