1/* 2 * Compatibility mode system call entry point for x86-64. 3 * 4 * Copyright 2000-2002 Andi Kleen, SuSE Labs. 5 */ 6#include "calling.h" 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 <linux/linkage.h> 17#include <linux/err.h> 18 19 .section .entry.text, "ax" 20 21/* 22 * 32-bit SYSENTER entry. 23 * 24 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 25 * on 64-bit kernels running on Intel CPUs. 26 * 27 * The SYSENTER instruction, in principle, should *only* occur in the 28 * vDSO. In practice, a small number of Android devices were shipped 29 * with a copy of Bionic that inlined a SYSENTER instruction. This 30 * never happened in any of Google's Bionic versions -- it only happened 31 * in a narrow range of Intel-provided versions. 32 * 33 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs. 34 * IF and VM in RFLAGS are cleared (IOW: interrupts are off). 35 * SYSENTER does not save anything on the stack, 36 * and does not save old RIP (!!!), RSP, or RFLAGS. 37 * 38 * Arguments: 39 * eax system call number 40 * ebx arg1 41 * ecx arg2 42 * edx arg3 43 * esi arg4 44 * edi arg5 45 * ebp user stack 46 * 0(%ebp) arg6 47 */ 48ENTRY(entry_SYSENTER_compat) 49 /* Interrupts are off on entry. */ 50 SWAPGS_UNSAFE_STACK 51 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 52 53 /* 54 * User tracing code (ptrace or signal handlers) might assume that 55 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 56 * syscall. Just in case the high bits are nonzero, zero-extend 57 * the syscall number. (This could almost certainly be deleted 58 * with no ill effects.) 59 */ 60 movl %eax, %eax 61 62 /* Construct struct pt_regs on stack */ 63 pushq $__USER32_DS /* pt_regs->ss */ 64 pushq %rbp /* pt_regs->sp (stashed in bp) */ 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, even 69 * if TF was set when SYSENTER started, it's clear by now. We fix 70 * that later using TIF_SINGLESTEP. 71 */ 72 pushfq /* pt_regs->flags (except IF = 0) */ 73 orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */ 74 pushq $__USER32_CS /* pt_regs->cs */ 75 xorq %r8,%r8 76 pushq %r8 /* pt_regs->ip = 0 (placeholder) */ 77 pushq %rax /* pt_regs->orig_ax */ 78 pushq %rdi /* pt_regs->di */ 79 pushq %rsi /* pt_regs->si */ 80 pushq %rdx /* pt_regs->dx */ 81 pushq %rcx /* pt_regs->cx */ 82 pushq $-ENOSYS /* pt_regs->ax */ 83 pushq %r8 /* pt_regs->r8 = 0 */ 84 pushq %r8 /* pt_regs->r9 = 0 */ 85 pushq %r8 /* pt_regs->r10 = 0 */ 86 pushq %r8 /* pt_regs->r11 = 0 */ 87 pushq %rbx /* pt_regs->rbx */ 88 pushq %rbp /* pt_regs->rbp (will be overwritten) */ 89 pushq %r8 /* pt_regs->r12 = 0 */ 90 pushq %r8 /* pt_regs->r13 = 0 */ 91 pushq %r8 /* pt_regs->r14 = 0 */ 92 pushq %r8 /* pt_regs->r15 = 0 */ 93 cld 94 95 /* 96 * SYSENTER doesn't filter flags, so we need to clear NT and AC 97 * ourselves. To save a few cycles, we can check whether 98 * either was set instead of doing an unconditional popfq. 99 * This needs to happen before enabling interrupts so that 100 * we don't get preempted with NT set. 101 * 102 * If TF is set, we will single-step all the way to here -- do_debug 103 * will ignore all the traps. (Yes, this is slow, but so is 104 * single-stepping in general. This allows us to avoid having 105 * a more complicated code to handle the case where a user program 106 * forces us to single-step through the SYSENTER entry code.) 107 * 108 * NB.: .Lsysenter_fix_flags is a label with the code under it moved 109 * out-of-line as an optimization: NT is unlikely to be set in the 110 * majority of the cases and instead of polluting the I$ unnecessarily, 111 * we're keeping that code behind a branch which will predict as 112 * not-taken and therefore its instructions won't be fetched. 113 */ 114 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp) 115 jnz .Lsysenter_fix_flags 116.Lsysenter_flags_fixed: 117 118 /* 119 * User mode is traced as though IRQs are on, and SYSENTER 120 * turned them off. 121 */ 122 TRACE_IRQS_OFF 123 124 movq %rsp, %rdi 125 call do_fast_syscall_32 126 /* XEN PV guests always use IRET path */ 127 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \ 128 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV 129 jmp sysret32_from_system_call 130 131.Lsysenter_fix_flags: 132 pushq $X86_EFLAGS_FIXED 133 popfq 134 jmp .Lsysenter_flags_fixed 135GLOBAL(__end_entry_SYSENTER_compat) 136ENDPROC(entry_SYSENTER_compat) 137 138/* 139 * 32-bit SYSCALL entry. 140 * 141 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here 142 * on 64-bit kernels running on AMD CPUs. 143 * 144 * The SYSCALL instruction, in principle, should *only* occur in the 145 * vDSO. In practice, it appears that this really is the case. 146 * As evidence: 147 * 148 * - The calling convention for SYSCALL has changed several times without 149 * anyone noticing. 150 * 151 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything 152 * user task that did SYSCALL without immediately reloading SS 153 * would randomly crash. 154 * 155 * - Most programmers do not directly target AMD CPUs, and the 32-bit 156 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD 157 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels 158 * because the SYSCALL instruction in legacy/native 32-bit mode (as 159 * opposed to compat mode) is sufficiently poorly designed as to be 160 * essentially unusable. 161 * 162 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves 163 * RFLAGS to R11, then loads new SS, CS, and RIP from previously 164 * programmed MSRs. RFLAGS gets masked by a value from another MSR 165 * (so CLD and CLAC are not needed). SYSCALL does not save anything on 166 * the stack and does not change RSP. 167 * 168 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode 169 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it). 170 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit 171 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes 172 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors). 173 * 174 * Arguments: 175 * eax system call number 176 * ecx return address 177 * ebx arg1 178 * ebp arg2 (note: not saved in the stack frame, should not be touched) 179 * edx arg3 180 * esi arg4 181 * edi arg5 182 * esp user stack 183 * 0(%esp) arg6 184 */ 185ENTRY(entry_SYSCALL_compat) 186 /* Interrupts are off on entry. */ 187 SWAPGS_UNSAFE_STACK 188 189 /* Stash user ESP and switch to the kernel stack. */ 190 movl %esp, %r8d 191 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 192 193 /* Zero-extending 32-bit regs, do not remove */ 194 movl %eax, %eax 195 196 /* Construct struct pt_regs on stack */ 197 pushq $__USER32_DS /* pt_regs->ss */ 198 pushq %r8 /* pt_regs->sp */ 199 pushq %r11 /* pt_regs->flags */ 200 pushq $__USER32_CS /* pt_regs->cs */ 201 pushq %rcx /* pt_regs->ip */ 202 pushq %rax /* pt_regs->orig_ax */ 203 pushq %rdi /* pt_regs->di */ 204 pushq %rsi /* pt_regs->si */ 205 pushq %rdx /* pt_regs->dx */ 206 pushq %rbp /* pt_regs->cx (stashed in bp) */ 207 pushq $-ENOSYS /* pt_regs->ax */ 208 xorq %r8,%r8 209 pushq %r8 /* pt_regs->r8 = 0 */ 210 pushq %r8 /* pt_regs->r9 = 0 */ 211 pushq %r8 /* pt_regs->r10 = 0 */ 212 pushq %r8 /* pt_regs->r11 = 0 */ 213 pushq %rbx /* pt_regs->rbx */ 214 pushq %rbp /* pt_regs->rbp (will be overwritten) */ 215 pushq %r8 /* pt_regs->r12 = 0 */ 216 pushq %r8 /* pt_regs->r13 = 0 */ 217 pushq %r8 /* pt_regs->r14 = 0 */ 218 pushq %r8 /* pt_regs->r15 = 0 */ 219 220 /* 221 * User mode is traced as though IRQs are on, and SYSENTER 222 * turned them off. 223 */ 224 TRACE_IRQS_OFF 225 226 movq %rsp, %rdi 227 call do_fast_syscall_32 228 /* XEN PV guests always use IRET path */ 229 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \ 230 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV 231 232 /* Opportunistic SYSRET */ 233sysret32_from_system_call: 234 TRACE_IRQS_ON /* User mode traces as IRQs on. */ 235 movq RBX(%rsp), %rbx /* pt_regs->rbx */ 236 movq RBP(%rsp), %rbp /* pt_regs->rbp */ 237 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */ 238 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */ 239 addq $RAX, %rsp /* Skip r8-r15 */ 240 popq %rax /* pt_regs->rax */ 241 popq %rdx /* Skip pt_regs->cx */ 242 popq %rdx /* pt_regs->dx */ 243 popq %rsi /* pt_regs->si */ 244 popq %rdi /* pt_regs->di */ 245 246 /* 247 * USERGS_SYSRET32 does: 248 * GSBASE = user's GS base 249 * EIP = ECX 250 * RFLAGS = R11 251 * CS = __USER32_CS 252 * SS = __USER_DS 253 * 254 * ECX will not match pt_regs->cx, but we're returning to a vDSO 255 * trampoline that will fix up RCX, so this is okay. 256 * 257 * R12-R15 are callee-saved, so they contain whatever was in them 258 * when the system call started, which is already known to user 259 * code. We zero R8-R10 to avoid info leaks. 260 */ 261 xorq %r8, %r8 262 xorq %r9, %r9 263 xorq %r10, %r10 264 movq RSP-ORIG_RAX(%rsp), %rsp 265 swapgs 266 sysretl 267END(entry_SYSCALL_compat) 268 269/* 270 * 32-bit legacy system call entry. 271 * 272 * 32-bit x86 Linux system calls traditionally used the INT $0x80 273 * instruction. INT $0x80 lands here. 274 * 275 * This entry point can be used by 32-bit and 64-bit programs to perform 276 * 32-bit system calls. Instances of INT $0x80 can be found inline in 277 * various programs and libraries. It is also used by the vDSO's 278 * __kernel_vsyscall fallback for hardware that doesn't support a faster 279 * entry method. Restarted 32-bit system calls also fall back to INT 280 * $0x80 regardless of what instruction was originally used to do the 281 * system call. 282 * 283 * This is considered a slow path. It is not used by most libc 284 * implementations on modern hardware except during process startup. 285 * 286 * Arguments: 287 * eax system call number 288 * ebx arg1 289 * ecx arg2 290 * edx arg3 291 * esi arg4 292 * edi arg5 293 * ebp arg6 294 */ 295ENTRY(entry_INT80_compat) 296 /* 297 * Interrupts are off on entry. 298 */ 299 PARAVIRT_ADJUST_EXCEPTION_FRAME 300 ASM_CLAC /* Do this early to minimize exposure */ 301 SWAPGS 302 303 /* 304 * User tracing code (ptrace or signal handlers) might assume that 305 * the saved RAX contains a 32-bit number when we're invoking a 32-bit 306 * syscall. Just in case the high bits are nonzero, zero-extend 307 * the syscall number. (This could almost certainly be deleted 308 * with no ill effects.) 309 */ 310 movl %eax, %eax 311 312 /* Construct struct pt_regs on stack (iret frame is already on stack) */ 313 pushq %rax /* pt_regs->orig_ax */ 314 pushq %rdi /* pt_regs->di */ 315 pushq %rsi /* pt_regs->si */ 316 pushq %rdx /* pt_regs->dx */ 317 pushq %rcx /* pt_regs->cx */ 318 pushq $-ENOSYS /* pt_regs->ax */ 319 xorq %r8,%r8 320 pushq %r8 /* pt_regs->r8 = 0 */ 321 pushq %r8 /* pt_regs->r9 = 0 */ 322 pushq %r8 /* pt_regs->r10 = 0 */ 323 pushq %r8 /* pt_regs->r11 = 0 */ 324 pushq %rbx /* pt_regs->rbx */ 325 pushq %rbp /* pt_regs->rbp */ 326 pushq %r12 /* pt_regs->r12 */ 327 pushq %r13 /* pt_regs->r13 */ 328 pushq %r14 /* pt_regs->r14 */ 329 pushq %r15 /* pt_regs->r15 */ 330 cld 331 332 /* 333 * User mode is traced as though IRQs are on, and the interrupt 334 * gate turned them off. 335 */ 336 TRACE_IRQS_OFF 337 338 movq %rsp, %rdi 339 call do_int80_syscall_32 340.Lsyscall_32_done: 341 342 /* Go back to user mode. */ 343 TRACE_IRQS_ON 344 SWAPGS 345 jmp restore_regs_and_iret 346END(entry_INT80_compat) 347 348 ALIGN 349GLOBAL(stub32_clone) 350 /* 351 * The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr). 352 * The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val). 353 * 354 * The native 64-bit kernel's sys_clone() implements the latter, 355 * so we need to swap arguments here before calling it: 356 */ 357 xchg %r8, %rcx 358 jmp sys_clone 359