subr_syscall.c

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/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (C) 1994, David Greenman
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 * Copyright (C) 2010 Konstantin Belousov <kib@freebsd.org>
 *
 * This code is derived from software contributed to Berkeley by
 * the University of Utah, and William Jolitz.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)trap.c        7.4 (Berkeley) 5/13/91
 */
 
#include "opt_capsicum.h"
#include "opt_ktrace.h"
 
__FBSDID("$FreeBSD$");
 
#include <sys/capsicum.h>
#include <sys/ktr.h>
#include <sys/vmmeter.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <security/audit/audit.h>
 
static inline void
syscallenter(struct thread *td)
{
        struct proc *p;
        struct syscall_args *sa;
        struct sysent *se;
        int error, traced;
        bool sy_thr_static;
 
        VM_CNT_INC(v_syscall);
        p = td->td_proc;
        sa = &td->td_sa;
 
        td->td_pticks = 0;
        if (__predict_false(td->td_cowgen != atomic_load_int(&p->p_cowgen)))
                thread_cow_update(td);
        traced = (p->p_flag & P_TRACED) != 0;
        if (__predict_false(traced || td->td_dbgflags & TDB_USERWR)) {
                PROC_LOCK(p);
                td->td_dbgflags &= ~TDB_USERWR;
                if (traced)
                        td->td_dbgflags |= TDB_SCE;
                PROC_UNLOCK(p);
        }
        error = (p->p_sysent->sv_fetch_syscall_args)(td);
        se = sa->callp;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_SYSCALL))
                ktrsyscall(sa->code, se->sy_narg, sa->args);
#endif
        KTR_START4(KTR_SYSC, "syscall", syscallname(p, sa->code),
            (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "arg0:%p", sa->args[0],
            "arg1:%p", sa->args[1], "arg2:%p", sa->args[2]);
 
        if (__predict_false(error != 0)) {
                td->td_errno = error;
                goto retval;
        }
 
        if (__predict_false(traced)) {
                PROC_LOCK(p);
                if (p->p_ptevents & PTRACE_SCE)
                        ptracestop((td), SIGTRAP, NULL);
                PROC_UNLOCK(p);
 
                if ((td->td_dbgflags & TDB_USERWR) != 0) {
                        /*
                         * Reread syscall number and arguments if debugger
                         * modified registers or memory.
                         */
                        error = (p->p_sysent->sv_fetch_syscall_args)(td);
                        se = sa->callp;
#ifdef KTRACE
                        if (KTRPOINT(td, KTR_SYSCALL))
                                ktrsyscall(sa->code, se->sy_narg, sa->args);
#endif
                        if (error != 0) {
                                td->td_errno = error;
                                goto retval;
                        }
                }
        }
 
#ifdef CAPABILITY_MODE
        /*
         * In capability mode, we only allow access to system calls
         * flagged with SYF_CAPENABLED.
         */
        if (__predict_false(IN_CAPABILITY_MODE(td) &&
            (se->sy_flags & SYF_CAPENABLED) == 0)) {
                td->td_errno = error = ECAPMODE;
                goto retval;
        }
#endif
 
        /*
         * Fetch fast sigblock value at the time of syscall entry to
         * handle sleepqueue primitives which might call cursig().
         */
        if (__predict_false(sigfastblock_fetch_always))
                (void)sigfastblock_fetch(td);
 
        /* Let system calls set td_errno directly. */
        KASSERT((td->td_pflags & TDP_NERRNO) == 0,
            ("%s: TDP_NERRNO set", __func__));
 
        sy_thr_static = (se->sy_thrcnt & SY_THR_STATIC) != 0;
 
        if (__predict_false(SYSTRACE_ENABLED() ||
            AUDIT_SYSCALL_ENTER(sa->code, td) ||
            !sy_thr_static)) {
                if (!sy_thr_static) {
                        error = syscall_thread_enter(td, se);
                        if (error != 0) {
                                td->td_errno = error;
                                goto retval;
                        }
                }
 
#ifdef KDTRACE_HOOKS
                /* Give the syscall:::entry DTrace probe a chance to fire. */
                if (__predict_false(se->sy_entry != 0))
                        (*systrace_probe_func)(sa, SYSTRACE_ENTRY, 0);
#endif
                error = (se->sy_call)(td, sa->args);
                /* Save the latest error return value. */
                if (__predict_false((td->td_pflags & TDP_NERRNO) != 0))
                        td->td_pflags &= ~TDP_NERRNO;
                else
                        td->td_errno = error;
 
                /*
                 * Note that some syscall implementations (e.g., sys_execve)
                 * will commit the audit record just before their final return.
                 * These were done under the assumption that nothing of interest
                 * would happen between their return and here, where we would
                 * normally commit the audit record.  These assumptions will
                 * need to be revisited should any substantial logic be added
                 * above.
                 */
                AUDIT_SYSCALL_EXIT(error, td);
 
#ifdef KDTRACE_HOOKS
                /* Give the syscall:::return DTrace probe a chance to fire. */
                if (__predict_false(se->sy_return != 0))
                        (*systrace_probe_func)(sa, SYSTRACE_RETURN,
                            error ? -1 : td->td_retval[0]);
#endif
 
                if (!sy_thr_static)
                        syscall_thread_exit(td, se);
        } else {
                error = (se->sy_call)(td, sa->args);
                /* Save the latest error return value. */
                if (__predict_false((td->td_pflags & TDP_NERRNO) != 0))
                        td->td_pflags &= ~TDP_NERRNO;
                else
                        td->td_errno = error;
        }
 
 retval:
        KTR_STOP4(KTR_SYSC, "syscall", syscallname(p, sa->code),
            (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "error:%d", error,
            "retval0:%#lx", td->td_retval[0], "retval1:%#lx",
            td->td_retval[1]);
        if (__predict_false(traced)) {
                PROC_LOCK(p);
                td->td_dbgflags &= ~TDB_SCE;
                PROC_UNLOCK(p);
        }
        (p->p_sysent->sv_set_syscall_retval)(td, error);
}
 
static inline void
syscallret(struct thread *td)
{
        struct proc *p;
        struct syscall_args *sa;
        ksiginfo_t ksi;
        int traced;
 
        KASSERT(td->td_errno != ERELOOKUP,
            ("ERELOOKUP not consumed syscall %d", td->td_sa.code));
 
        p = td->td_proc;
        sa = &td->td_sa;
        if (__predict_false(td->td_errno == ENOTCAPABLE ||
            td->td_errno == ECAPMODE)) {
                if ((trap_enotcap ||
                    (p->p_flag2 & P2_TRAPCAP) != 0) && IN_CAPABILITY_MODE(td)) {
                        ksiginfo_init_trap(&ksi);
                        ksi.ksi_signo = SIGTRAP;
                        ksi.ksi_errno = td->td_errno;
                        ksi.ksi_code = TRAP_CAP;
                        ksi.ksi_info.si_syscall = sa->original_code;
                        trapsignal(td, &ksi);
                }
        }
 
        /*
         * Handle reschedule and other end-of-syscall issues
         */
        userret(td, td->td_frame);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_SYSRET)) {
                ktrsysret(sa->code, td->td_errno, td->td_retval[0]);
        }
#endif
 
        traced = 0;
        if (__predict_false(p->p_flag & P_TRACED)) {
                traced = 1;
                PROC_LOCK(p);
                td->td_dbgflags |= TDB_SCX;
                PROC_UNLOCK(p);
        }
        if (__predict_false(traced ||
            (td->td_dbgflags & (TDB_EXEC | TDB_FORK)) != 0)) {
                PROC_LOCK(p);
                /*
                 * Linux debuggers expect an additional stop for exec,
                 * between the usual syscall entry and exit.  Raise
                 * the exec event now and then clear TDB_EXEC so that
                 * the next stop is reported as a syscall exit by
                 * linux_ptrace_status().
                 *
                 * We are accessing p->p_pptr without any additional
                 * locks here: it cannot change while p is kept locked;
                 * while the debugger could in theory change its ABI
                 * while tracing another process, the outcome of such
                 * a race wouln't be deterministic anyway.
                 */
                if (traced && (td->td_dbgflags & TDB_EXEC) != 0 &&
                    SV_PROC_ABI(p->p_pptr) == SV_ABI_LINUX) {
                        ptracestop(td, SIGTRAP, NULL);
                        td->td_dbgflags &= ~TDB_EXEC;
                }
                /*
                 * If tracing the execed process, trap to the debugger
                 * so that breakpoints can be set before the program
                 * executes.  If debugger requested tracing of syscall
                 * returns, do it now too.
                 */
                if (traced &&
                    ((td->td_dbgflags & (TDB_FORK | TDB_EXEC)) != 0 ||
                    (p->p_ptevents & PTRACE_SCX) != 0))
                        ptracestop(td, SIGTRAP, NULL);
                td->td_dbgflags &= ~(TDB_SCX | TDB_EXEC | TDB_FORK);
                PROC_UNLOCK(p);
        }
}