entry_64_compat.S (11044B)
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 "calling.h" 8#include <asm/asm-offsets.h> 9#include <asm/current.h> 10#include <asm/errno.h> 11#include <asm/ia32_unistd.h> 12#include <asm/thread_info.h> 13#include <asm/segment.h> 14#include <asm/irqflags.h> 15#include <asm/asm.h> 16#include <asm/smap.h> 17#include <linux/linkage.h> 18#include <linux/err.h> 19 20 .section .entry.text, "ax" 21 22/* 23 * 32-bit SYSENTER entry. 24 * 25 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 26 * on 64-bit kernels running on Intel CPUs. 27 * 28 * The SYSENTER instruction, in principle, should *only* occur in the 29 * vDSO. In practice, a small number of Android devices were shipped 30 * with a copy of Bionic that inlined a SYSENTER instruction. This 31 * never happened in any of Google's Bionic versions -- it only happened 32 * in a narrow range of Intel-provided versions. 33 * 34 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs. 35 * IF and VM in RFLAGS are cleared (IOW: interrupts are off). 36 * SYSENTER does not save anything on the stack, 37 * and does not save old RIP (!!!), RSP, or RFLAGS. 38 * 39 * Arguments: 40 * eax system call number 41 * ebx arg1 42 * ecx arg2 43 * edx arg3 44 * esi arg4 45 * edi arg5 46 * ebp user stack 47 * 0(%ebp) arg6 48 */ 49SYM_CODE_START(entry_SYSENTER_compat) 50 UNWIND_HINT_EMPTY 51 ENDBR 52 /* Interrupts are off on entry. */ 53 swapgs 54 55 pushq %rax 56 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 57 popq %rax 58 59 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 60 61 /* Construct struct pt_regs on stack */ 62 pushq $__USER32_DS /* pt_regs->ss */ 63 pushq $0 /* pt_regs->sp = 0 (placeholder) */ 64 65 /* 66 * Push flags. This is nasty. First, interrupts are currently 67 * off, but we need pt_regs->flags to have IF set. Second, if TS 68 * was set in usermode, it's still set, and we're singlestepping 69 * through this code. do_SYSENTER_32() will fix up IF. 70 */ 71 pushfq /* pt_regs->flags (except IF = 0) */ 72 pushq $__USER32_CS /* pt_regs->cs */ 73 pushq $0 /* pt_regs->ip = 0 (placeholder) */ 74SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) 75 76 /* 77 * User tracing code (ptrace or signal handlers) might assume that 78 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 79 * syscall. Just in case the high bits are nonzero, zero-extend 80 * the syscall number. (This could almost certainly be deleted 81 * with no ill effects.) 82 */ 83 movl %eax, %eax 84 85 pushq %rax /* pt_regs->orig_ax */ 86 PUSH_AND_CLEAR_REGS rax=$-ENOSYS 87 UNWIND_HINT_REGS 88 89 cld 90 91 /* 92 * SYSENTER doesn't filter flags, so we need to clear NT and AC 93 * ourselves. To save a few cycles, we can check whether 94 * either was set instead of doing an unconditional popfq. 95 * This needs to happen before enabling interrupts so that 96 * we don't get preempted with NT set. 97 * 98 * If TF is set, we will single-step all the way to here -- do_debug 99 * will ignore all the traps. (Yes, this is slow, but so is 100 * single-stepping in general. This allows us to avoid having 101 * a more complicated code to handle the case where a user program 102 * forces us to single-step through the SYSENTER entry code.) 103 * 104 * NB.: .Lsysenter_fix_flags is a label with the code under it moved 105 * out-of-line as an optimization: NT is unlikely to be set in the 106 * majority of the cases and instead of polluting the I$ unnecessarily, 107 * we're keeping that code behind a branch which will predict as 108 * not-taken and therefore its instructions won't be fetched. 109 */ 110 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp) 111 jnz .Lsysenter_fix_flags 112.Lsysenter_flags_fixed: 113 114 movq %rsp, %rdi 115 call do_SYSENTER_32 116 /* XEN PV guests always use IRET path */ 117 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 118 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 119 jmp sysret32_from_system_call 120 121.Lsysenter_fix_flags: 122 pushq $X86_EFLAGS_FIXED 123 popfq 124 jmp .Lsysenter_flags_fixed 125SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL) 126 ANNOTATE_NOENDBR // is_sysenter_singlestep 127SYM_CODE_END(entry_SYSENTER_compat) 128 129/* 130 * 32-bit SYSCALL entry. 131 * 132 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 133 * on 64-bit kernels running on AMD CPUs. 134 * 135 * The SYSCALL instruction, in principle, should *only* occur in the 136 * vDSO. In practice, it appears that this really is the case. 137 * As evidence: 138 * 139 * - The calling convention for SYSCALL has changed several times without 140 * anyone noticing. 141 * 142 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything 143 * user task that did SYSCALL without immediately reloading SS 144 * would randomly crash. 145 * 146 * - Most programmers do not directly target AMD CPUs, and the 32-bit 147 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD 148 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels 149 * because the SYSCALL instruction in legacy/native 32-bit mode (as 150 * opposed to compat mode) is sufficiently poorly designed as to be 151 * essentially unusable. 152 * 153 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves 154 * RFLAGS to R11, then loads new SS, CS, and RIP from previously 155 * programmed MSRs. RFLAGS gets masked by a value from another MSR 156 * (so CLD and CLAC are not needed). SYSCALL does not save anything on 157 * the stack and does not change RSP. 158 * 159 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode 160 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it). 161 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit 162 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes 163 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors). 164 * 165 * Arguments: 166 * eax system call number 167 * ecx return address 168 * ebx arg1 169 * ebp arg2 (note: not saved in the stack frame, should not be touched) 170 * edx arg3 171 * esi arg4 172 * edi arg5 173 * esp user stack 174 * 0(%esp) arg6 175 */ 176SYM_CODE_START(entry_SYSCALL_compat) 177 UNWIND_HINT_EMPTY 178 ENDBR 179 /* Interrupts are off on entry. */ 180 swapgs 181 182 /* Stash user ESP */ 183 movl %esp, %r8d 184 185 /* Use %rsp as scratch reg. User ESP is stashed in r8 */ 186 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp 187 188 /* Switch to the kernel stack */ 189 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 190 191SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) 192 ANNOTATE_NOENDBR 193 194 /* Construct struct pt_regs on stack */ 195 pushq $__USER32_DS /* pt_regs->ss */ 196 pushq %r8 /* pt_regs->sp */ 197 pushq %r11 /* pt_regs->flags */ 198 pushq $__USER32_CS /* pt_regs->cs */ 199 pushq %rcx /* pt_regs->ip */ 200SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL) 201 movl %eax, %eax /* discard orig_ax high bits */ 202 pushq %rax /* pt_regs->orig_ax */ 203 PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS 204 UNWIND_HINT_REGS 205 206 movq %rsp, %rdi 207 call do_fast_syscall_32 208 /* XEN PV guests always use IRET path */ 209 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ 210 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV 211 212 /* Opportunistic SYSRET */ 213sysret32_from_system_call: 214 /* 215 * We are not going to return to userspace from the trampoline 216 * stack. So let's erase the thread stack right now. 217 */ 218 STACKLEAK_ERASE 219 220 movq RBX(%rsp), %rbx /* pt_regs->rbx */ 221 movq RBP(%rsp), %rbp /* pt_regs->rbp */ 222 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */ 223 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */ 224 addq $RAX, %rsp /* Skip r8-r15 */ 225 popq %rax /* pt_regs->rax */ 226 popq %rdx /* Skip pt_regs->cx */ 227 popq %rdx /* pt_regs->dx */ 228 popq %rsi /* pt_regs->si */ 229 popq %rdi /* pt_regs->di */ 230 231 /* 232 * USERGS_SYSRET32 does: 233 * GSBASE = user's GS base 234 * EIP = ECX 235 * RFLAGS = R11 236 * CS = __USER32_CS 237 * SS = __USER_DS 238 * 239 * ECX will not match pt_regs->cx, but we're returning to a vDSO 240 * trampoline that will fix up RCX, so this is okay. 241 * 242 * R12-R15 are callee-saved, so they contain whatever was in them 243 * when the system call started, which is already known to user 244 * code. We zero R8-R10 to avoid info leaks. 245 */ 246 movq RSP-ORIG_RAX(%rsp), %rsp 247SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL) 248 ANNOTATE_NOENDBR 249 250 /* 251 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored 252 * on the process stack which is not mapped to userspace and 253 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3 254 * switch until after after the last reference to the process 255 * stack. 256 * 257 * %r8/%r9 are zeroed before the sysret, thus safe to clobber. 258 */ 259 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9 260 261 xorl %r8d, %r8d 262 xorl %r9d, %r9d 263 xorl %r10d, %r10d 264 swapgs 265 sysretl 266SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL) 267 ANNOTATE_NOENDBR 268 int3 269SYM_CODE_END(entry_SYSCALL_compat) 270 271/* 272 * 32-bit legacy system call entry. 273 * 274 * 32-bit x86 Linux system calls traditionally used the INT $0x80 275 * instruction. INT $0x80 lands here. 276 * 277 * This entry point can be used by 32-bit and 64-bit programs to perform 278 * 32-bit system calls. Instances of INT $0x80 can be found inline in 279 * various programs and libraries. It is also used by the vDSO's 280 * __kernel_vsyscall fallback for hardware that doesn't support a faster 281 * entry method. Restarted 32-bit system calls also fall back to INT 282 * $0x80 regardless of what instruction was originally used to do the 283 * system call. 284 * 285 * This is considered a slow path. It is not used by most libc 286 * implementations on modern hardware except during process startup. 287 * 288 * Arguments: 289 * eax system call number 290 * ebx arg1 291 * ecx arg2 292 * edx arg3 293 * esi arg4 294 * edi arg5 295 * ebp arg6 296 */ 297SYM_CODE_START(entry_INT80_compat) 298 UNWIND_HINT_EMPTY 299 ENDBR 300 /* 301 * Interrupts are off on entry. 302 */ 303 ASM_CLAC /* Do this early to minimize exposure */ 304 SWAPGS 305 306 /* 307 * User tracing code (ptrace or signal handlers) might assume that 308 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 309 * syscall. Just in case the high bits are nonzero, zero-extend 310 * the syscall number. (This could almost certainly be deleted 311 * with no ill effects.) 312 */ 313 movl %eax, %eax 314 315 /* switch to thread stack expects orig_ax and rdi to be pushed */ 316 pushq %rax /* pt_regs->orig_ax */ 317 318 /* Need to switch before accessing the thread stack. */ 319 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 320 321 /* In the Xen PV case we already run on the thread stack. */ 322 ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV 323 324 movq %rsp, %rax 325 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 326 327 pushq 5*8(%rax) /* regs->ss */ 328 pushq 4*8(%rax) /* regs->rsp */ 329 pushq 3*8(%rax) /* regs->eflags */ 330 pushq 2*8(%rax) /* regs->cs */ 331 pushq 1*8(%rax) /* regs->ip */ 332 pushq 0*8(%rax) /* regs->orig_ax */ 333.Lint80_keep_stack: 334 335 PUSH_AND_CLEAR_REGS rax=$-ENOSYS 336 UNWIND_HINT_REGS 337 338 cld 339 340 movq %rsp, %rdi 341 call do_int80_syscall_32 342 jmp swapgs_restore_regs_and_return_to_usermode 343SYM_CODE_END(entry_INT80_compat)