arch/x86/entry/entry_64_compat.S

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