kernel/syscalls/syscalls.cpp

// Copyright 2016 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#include <err.h>
#include <kernel/stats.h>
#include <kernel/thread.h>
#include <lib/ktrace.h>
#include <lib/vdso.h>
#include <object/process_dispatcher.h>
#include <platform.h>
#include <syscalls/syscalls.h>
#include <trace.h>
#include <zircon/zx-syscall-numbers.h>

#include <inttypes.h>
#include <stdint.h>

#include "priv.h"
#include "vdso-valid-sysret.h"

#define LOCAL_TRACE 0

__NO_INLINE static int sys_invalid_syscall(uint64_t num, uint64_t pc,
                        uintptr_t vdso_code_address) {
    LTRACEF("invalid syscall %lu from PC %#lx vDSO code %#lx\n",
            num, pc, vdso_code_address);
    thread_signal_policy_exception();
    return ZX_ERR_BAD_SYSCALL;
}

// N.B. Interrupts must be disabled on entry and they will be disabled on exit.
// The reason is the two calls two arch_curr_cpu_num in the ktrace calls: we
// don't want the cpu changing during the call.

__NO_INLINE static void syscall_pre(uint64_t syscall_num, uint64_t pc, ProcessDispatcher** current_process, uintptr_t* vdso_code_address) {
    ktrace_tiny(TAG_SYSCALL_ENTER, (static_cast<uint32_t>(syscall_num) << 8) | arch_curr_cpu_num());

    CPU_STATS_INC(syscalls);

    /* re-enable interrupts to maintain kernel preemptiveness
       This must be done after the above ktrace_tiny call, and after the
       above CPU_STATS_INC call as it also calls arch_curr_cpu_num. */
    arch_enable_ints();

    LTRACEF_LEVEL(2, "t %p syscall num %" PRIu64 " ip/pc %#" PRIx64 "\n",
                  get_current_thread(), syscall_num, pc);

    *current_process = ProcessDispatcher::GetCurrent();
    *vdso_code_address = (*current_process)->vdso_code_address();
}

__NO_INLINE static syscall_result syscall_post(uint64_t syscall_num, uint64_t ret) {
    LTRACEF_LEVEL(2, "t %p ret %#" PRIx64 "\n", get_current_thread(), ret);

    /* re-disable interrupts on the way out
       This must be done before the below ktrace_tiny call. */
    arch_disable_ints();

    ktrace_tiny(TAG_SYSCALL_EXIT, (static_cast<uint32_t>(syscall_num << 8)) | arch_curr_cpu_num());

    // The assembler caller will re-disable interrupts at the appropriate time.
    return {ret, thread_is_signaled(get_current_thread())};
}

template <typename T>
static inline syscall_result do_syscall(uint64_t syscall_num, uint64_t pc,
                                        bool (*valid_pc)(uintptr_t), T make_call) {

    ProcessDispatcher* current_process;
    uintptr_t vdso_code_address;

    // call the shared pre syscall routine
    syscall_pre(syscall_num, pc, &current_process, &vdso_code_address);

    uint64_t ret;
    if (unlikely(!valid_pc(pc - vdso_code_address))) {
        ret = sys_invalid_syscall(syscall_num, pc, vdso_code_address);
    } else {
        ret = make_call(current_process);
    }

    // call the shared post-syscall routine
    return syscall_post(syscall_num, ret);
}

syscall_result unknown_syscall(uint64_t syscall_num, uint64_t pc) {
    return do_syscall(syscall_num, pc,
                      [](uintptr_t) { return false; },
                      [&](ProcessDispatcher*) {
                          __builtin_unreachable();
                          return ZX_ERR_INTERNAL;
                      });
}

// Autogenerated per-syscall wrapper functions.
#include <zircon/syscall-kernel-wrappers.inc>