syscall.c

/*
 * Functions for actually doing the system calls.
 */

#include <errno.h>
#include <string.h>
#include <signal.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>

#include "arch.h"
#include "child.h"
#include "pids.h"
#include "random.h"
#include "sanitise.h"
#include "shm.h"
#include "syscall.h"
#include "log.h"
#include "tables.h"
#include "uid.h"
#include "utils.h"

#ifdef ARCH_IS_BIARCH
/*
 * This routine does 32 bit syscalls on 64 bit kernel.
 * 32-on-32 will just use syscall() directly from do_syscall() because do32bit flag is biarch only.
 */
static long syscall32(unsigned int call,
	unsigned long a1, unsigned long a2, unsigned long a3,
	unsigned long a4, unsigned long a5, unsigned long a6)
{
	long __res = 0;

#if defined(DO_32_SYSCALL)
	/* If we have CONFIG_IA32_EMULATION unset, we will segfault.
	 * Detect this case, and force 64-bit only.
	 */
	if (shm->syscalls32_succeeded == FALSE) {
		if (shm->syscalls32_attempted >= (max_children * 2)) {
			unsigned int i;

			lock(&shm->syscalltable_lock);

			/* check another thread didn't already do this. */
			if (shm->nr_active_32bit_syscalls == 0)
				goto already_done;

			output(0, "Tried %d 32-bit syscalls unsuccessfully. Disabling all 32-bit syscalls.\n",
					shm->syscalls32_attempted);

			for (i = 0; i < max_nr_32bit_syscalls; i++) {
				struct syscallentry *entry = syscalls[i].entry;

				if (entry->active_number != 0)
					deactivate_syscall(i, TRUE);
			}
already_done:
			unlock(&shm->syscalltable_lock);
		}

		shm->syscalls32_attempted++;
	}

	DO_32_SYSCALL

	if ((unsigned long)(__res) >= (unsigned long)(-133)) {
		errno = -(__res);
		__res = -1;
	}

	shm->syscalls32_succeeded = TRUE;

#else
	#error Implement 32-on-64 syscall macro for this architecture.
#endif
	return __res;
}
#else
#define syscall32(a,b,c,d,e,f,g) 0
#endif /* ARCH_IS_BIARCH */

static void __do_syscall(struct syscallrecord *rec)
{
	int nr, call;
	unsigned long ret = 0;
	bool needalarm;

	nr = rec->nr;

	/* Some architectures (IA64/MIPS) start their Linux syscalls
	 * At non-zero, and have other ABIs below.
	 */
	call = nr + SYSCALL_OFFSET;

	needalarm = syscalls[nr].entry->flags & NEED_ALARM;
	if (needalarm)
		(void)alarm(1);

	errno = 0;

	shm_ro();
	if (rec->do32bit == FALSE)
		ret = syscall(call, rec->a1, rec->a2, rec->a3, rec->a4, rec->a5, rec->a6);
	else
		ret = syscall32(call, rec->a1, rec->a2, rec->a3, rec->a4, rec->a5, rec->a6);
	shm_rw();

	/* We returned! */
	shm->stats.total_syscalls_done++;

	lock(&rec->lock);
	(void)gettimeofday(&rec->tv, NULL);

	rec->op_nr++;
	rec->errno_post = errno;
	rec->retval = ret;
	rec->state = AFTER;
	unlock(&rec->lock);

	if (IS_ERR(ret))
		shm->stats.failures++;
	else
		shm->stats.successes++;

	if (needalarm)
		(void)alarm(0);
}

/* This is a special case for things like execve, which would replace our
 * child process with something unknown to us. We use a 'throwaway' process
 * to do the execve in, and let it run for a max of a seconds before we kill it
 */
static void do_extrafork(struct syscallrecord *rec)
{
	pid_t pid = 0;
	pid_t extrapid;

	extrapid = fork();
	if (extrapid == 0) {
		/* grand-child */
		char childname[]="trinity-subchild";
		prctl(PR_SET_NAME, (unsigned long) &childname);

		rec->state = GOING_AWAY;
		__do_syscall(rec);
		/* if this was for eg. an successful execve, we should never get here.
		 * if it failed though... */
		shm->stats.failures++;
		_exit(EXIT_SUCCESS);
	}

	/* child */
	while (pid == 0) {
		int childstatus;

		pid = waitpid(extrapid, &childstatus, WUNTRACED | WCONTINUED | WNOHANG);
		if (pid_alive(extrapid) == TRUE)
			kill(extrapid, SIGKILL);
	}
	shm->stats.successes++;
}


void do_syscall(struct syscallrecord *rec)
{
	struct syscallentry *entry;
	unsigned int call;

	call = rec->nr;
	entry = syscalls[call].entry;

	rec->state = BEFORE;

	if (entry->flags & EXTRA_FORK)
		do_extrafork(rec);
	else
		 /* common-case, do the syscall in this child process. */
		__do_syscall(rec);
}

static void check_retval_documented(struct syscallrecord *rec, struct syscallentry *entry)
{
	struct errnos *errnos;
	unsigned int i;

	/* Just return silently if ENOSYS, we'll disable it immediately afterwards. */
	if (rec->errno_post == ENOSYS)
		return;

	/* Only check syscalls we've documented so far. */
	errnos = &entry->errnos;
	if (errnos->num == 0)
		return;

	lock(&shm->syscalltable_lock);

	/* Check against the list of known return values. */
	for (i = 0; i < errnos->num; i++) {
		if (rec->errno_post == errnos->values[i])
			goto out;
	}

	/* if we get here, we have a return value we don't know.
	 * find space for it, and store it so we don't warn again */

	if (errnos->values[i] == 0) {
		errnos->values[i] = rec->errno_post;
		errnos->num++;

		//TODO: if this was the 32bit syscall, we should adjust the 64bit one too.
		// and vice-versa.

		//output(0, "%s%s\n", rec->prebuffer, rec->postbuffer);
		output(0, "%s%s returned an undocumented return value (%d:%s)\n",
			entry->name,
			rec->do32bit == TRUE ? ":[32BIT]" : "",
			rec->errno_post, strerror(rec->errno_post));
	}

out:
	unlock(&shm->syscalltable_lock);
}

/*
 * If the syscall doesn't exist don't bother calling it next time.
 * Some syscalls return ENOSYS depending on their arguments, we mark
 * those as IGNORE_ENOSYS and keep calling them.
 */
static void deactivate_enosys(struct syscallrecord *rec, struct syscallentry *entry, unsigned int call)
{
	if (rec->errno_post != ENOSYS)
		return;

	if (entry->flags & IGNORE_ENOSYS)
		return;

	lock(&shm->syscalltable_lock);

	/* check another thread didn't already do this. */
	if (entry->active_number == 0)
		goto already_done;

	output(1, "%s (%d%s) returned ENOSYS, marking as inactive.\n",
		entry->name,
		call + SYSCALL_OFFSET,
		rec->do32bit == TRUE ? ":[32BIT]" : "");

	deactivate_syscall(call, rec->do32bit);
already_done:
	unlock(&shm->syscalltable_lock);
}

void handle_syscall_ret(struct syscallrecord *rec)
{
	struct syscallentry *entry;
	struct syscallrecord *previous;
	unsigned int call;

	call = rec->nr;
	entry = syscalls[call].entry;

	if (rec->retval == -1UL) {
		/* only check syscalls that completed. */
		if (rec->state == AFTER) {
			check_retval_documented(rec, entry);
			deactivate_enosys(rec, entry, call);
		}
	}

	if (entry->post)
	    entry->post(rec);

	/* store info for debugging. */
	previous = &this_child->previous;
	memcpy(previous, rec, sizeof(struct syscallrecord));
	previous->state = DONE;

	check_uid();

	generic_free_arg(rec);
}