/* SPDX-License-Identifier: GPL-2.0 */
/*
* syscall_numbering.c - test calling the x86-64 kernel with various
* valid and invalid system call numbers.
*
* Copyright (c) 2018 Andrew Lutomirski
*/
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <sysexits.h>
#include <sys/ptrace.h>
#include <sys/user.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <linux/ptrace.h>
/* Common system call numbers */
#define SYS_READ 0
#define SYS_WRITE 1
#define SYS_GETPID 39
/* x64-only system call numbers */
#define X64_IOCTL 16
#define X64_READV 19
#define X64_WRITEV 20
/* x32-only system call numbers (without X32_BIT) */
#define X32_IOCTL 514
#define X32_READV 515
#define X32_WRITEV 516
#define X32_BIT 0x40000000
static int nullfd = -1; /* File descriptor for /dev/null */
static bool with_x32; /* x32 supported on this kernel? */
enum ptrace_pass {
PTP_NOTHING,
PTP_GETREGS,
PTP_WRITEBACK,
PTP_FUZZRET,
PTP_FUZZHIGH,
PTP_INTNUM,
PTP_DONE
};
static const char * const ptrace_pass_name[] =
{
[PTP_NOTHING] = "just stop, no data read",
[PTP_GETREGS] = "only getregs",
[PTP_WRITEBACK] = "getregs, unmodified setregs",
[PTP_FUZZRET] = "modifying the default return",
[PTP_FUZZHIGH] = "clobbering the top 32 bits",
[PTP_INTNUM] = "sign-extending the syscall number",
};
/*
* Shared memory block between tracer and test
*/
struct shared {
unsigned int nerr; /* Total error count */
unsigned int indent; /* Message indentation level */
enum ptrace_pass ptrace_pass;
bool probing_syscall; /* In probe_syscall() */
};
static volatile struct shared *sh;
static inline unsigned int offset(void)
{
unsigned int level = sh ? sh->indent : 0;
return 8 + level * 4;
}
#define msg(lvl, fmt, ...) printf("%-*s" fmt, offset(), "[" #lvl "]", \
## __VA_ARGS__)
#define run(fmt, ...) msg(RUN, fmt, ## __VA_ARGS__)
#define info(fmt, ...) msg(INFO, fmt, ## __VA_ARGS__)
#define ok(fmt, ...) msg(OK, fmt, ## __VA_ARGS__)
#define fail(fmt, ...) \
do { \
msg(FAIL, fmt, ## __VA_ARGS__); \
sh->nerr++; \
} while (0)
#define crit(fmt, ...) \
do { \
sh->indent = 0; \
msg(FAIL, fmt, ## __VA_ARGS__); \
msg(SKIP, "Unable to run test\n"); \
exit(EX_OSERR); \
} while (0)
/* Sentinel for ptrace-modified return value */
#define MODIFIED_BY_PTRACE -9999
/*
* Directly invokes the given syscall with nullfd as the first argument
* and the rest zero. Avoids involving glibc wrappers in case they ever
* end up intercepting some system calls for some reason, or modify
* the system call number itself.
*/
static long long probe_syscall(int msb, int lsb)
{
register long long arg1 asm("rdi") = nullfd;
register long long arg2 asm("rsi") = 0;
register long long arg3 asm("rdx") = 0;
register long long arg4 asm("r10") = 0;
register long long arg5 asm("r8") = 0;
register long long arg6 asm("r9") = 0;
long long nr = ((long long)msb << 32) | (unsigned int)lsb;
long long ret;
/*
* We pass in an extra copy of the extended system call number
* in %rbx, so we can examine it from the ptrace handler without
* worrying about it being possibly modified. This is to test
* the validity of struct user regs.orig_rax a.k.a.
* struct pt_regs.orig_ax.
*/
sh->probing_syscall = true;
asm volatile("syscall"
: "=a" (ret)
: "a" (nr), "b" (nr),
"r" (arg1), "r" (arg2), "r" (arg3),
"r" (arg4), "r" (arg5), "r" (arg6)
: "rcx", "r11", "memory", "cc");
sh->probing_syscall = false;
return ret;
}
static const char *syscall_str(int msb, int start, int end)
{
static char buf[64];
const char * const type = (start & X32_BIT) ? "x32" : "x64";
int lsb = start;
/*
* Improve readability by stripping the x32 bit, but round
* toward zero so we don't display -1 as -1073741825.
*/
if (lsb < 0)
lsb |= X32_BIT;
else
lsb &= ~X32_BIT;
if (start == end)
snprintf(buf, sizeof buf, "%s syscall %d:%d",
type, msb, lsb);
else
snprintf(buf, sizeof buf, "%s syscalls %d:%d..%d",
type, msb, lsb, lsb + (end-start));
return buf;
}
static unsigned int _check_for(int msb, int start, int end, long long expect,
const char *expect_str)
{
unsigned int err = 0;
sh->indent++;
if (start != end)
sh->indent++;
for (int nr = start; nr <= end; nr++) {
long long ret = probe_syscall(msb, nr);
if (ret != expect) {
fail("%s returned %lld, but it should have returned %s\n",
syscall_str(msb, nr, nr),
ret, expect_str);
err++;
}
}
if (start != end)
sh->indent--;
if (err) {
if (start != end)
fail("%s had %u failure%s\n",
syscall_str(msb, start, end),
err, err == 1 ? "s" : "");
} else {
ok("%s returned %s as expected\n",
syscall_str(msb, start, end), expect_str);
}
sh->indent--;
return err;
}
#define check_for(msb,start,end,expect) \
_check_for(msb,start,end,expect,#expect)
static bool check_zero(int msb, int nr)
{
return check_for(msb, nr, nr, 0);
}
static bool check_enosys(int msb, int nr)
{
return check_for(msb, nr, nr, -ENOSYS);
}
/*
* Anyone diagnosing a failure will want to know whether the kernel
* supports x32. Tell them. This can also be used to conditionalize
* tests based on existence or nonexistence of x32.
*/
static bool test_x32(void)
{
long long ret;
pid_t mypid = getpid();
run("Checking for x32 by calling x32 getpid()\n");
ret = probe_syscall(0, SYS_GETPID | X32_BIT);
sh->indent++;
if (ret == mypid) {
info("x32 is supported\n");
with_x32 = true;
} else if (ret == -ENOSYS) {
info("x32 is not supported\n");
with_x32 = false;
} else {
fail("x32 getpid() returned %lld, but it should have returned either %lld or -ENOSYS\n", ret, (long long)mypid);
with_x32 = false;
}
sh->indent--;
return with_x32;
}
static void test_syscalls_common(int msb)
{
enum ptrace_pass pass = sh->ptrace_pass;
run("Checking some common syscalls as 64 bit\n");
check_zero(msb, SYS_READ);
check_zero(msb, SYS_WRITE);
run("Checking some 64-bit only syscalls as 64 bit\n");
check_zero(msb, X64_READV);
check_zero(msb, X64_WRITEV);
run("Checking out of range system calls\n");
check_for(msb, -64, -2, -ENOSYS);
if (pass >= PTP_FUZZRET)
check_for(msb, -1, -1, MODIFIED_BY_PTRACE);
else
check_for(msb, -1, -1, -ENOSYS);
check_for(msb, X32_BIT-64, X32_BIT-1, -ENOSYS);
check_for(msb, -64-X32_BIT, -1-X32_BIT, -ENOSYS);
check_for(msb, INT_MAX-64, INT_MAX-1, -ENOSYS);
}
static void test_syscalls_with_x32(int msb)
{
/*
* Syscalls 512-547 are "x32" syscalls. They are
* intended to be called with the x32 (0x40000000) bit
* set. Calling them without the x32 bit set is
* nonsense and should not work.
*/
run("Checking x32 syscalls as 64 bit\n");
check_for(msb, 512, 547, -ENOSYS);
run("Checking some common syscalls as x32\n");
check_zero(msb, SYS_READ | X32_BIT);
check_zero(msb, SYS_WRITE | X32_BIT);
run("Checking some x32 syscalls as x32\n");
check_zero(msb, X32_READV | X32_BIT);
check_zero(msb, X32_WRITEV | X32_BIT);
run("Checking some 64-bit syscalls as x32\n");
check_enosys(msb, X64_IOCTL | X32_BIT);
check_enosys(msb, X64_READV | X32_BIT);
check_enosys(msb, X64_WRITEV | X32_BIT);
}
static void test_syscalls_without_x32(int msb)
{
run("Checking for absence of x32 system calls\n");
check_for(msb, 0 | X32_BIT, 999 | X32_BIT, -ENOSYS);
}
static void test_syscall_numbering(void)
{
static const int msbs[] = {
0, 1, -1, X32_BIT-1, X32_BIT, X32_BIT-1, -X32_BIT, INT_MAX,
INT_MIN, INT_MIN+1
};
sh->indent++;
/*
* The MSB is supposed to be ignored, so we loop over a few
* to test that out.
*/
for (size_t i = 0; i < sizeof(msbs)/sizeof(msbs[0]); i++) {
int msb = msbs[i];
run("Checking system calls with msb = %d (0x%x)\n",
msb, msb);
sh->indent++;
test_syscalls_common(msb);
if (with_x32)
test_syscalls_with_x32(msb);
else
test_syscalls_without_x32(msb);
sh->indent--;
}
sh->indent--;
}
static void syscall_numbering_tracee(void)
{
enum ptrace_pass pass;
if (ptrace(PTRACE_TRACEME, 0, 0, 0)) {
crit("Failed to request tracing\n");
return;
}
raise(SIGSTOP);
for (sh->ptrace_pass = pass = PTP_NOTHING; pass < PTP_DONE;
sh->ptrace_pass = ++pass) {
run("Running tests under ptrace: %s\n", ptrace_pass_name[pass]);
test_syscall_numbering();
}
}
static void mess_with_syscall(pid_t testpid, enum ptrace_pass pass)
{
struct user_regs_struct regs;
sh->probing_syscall = false; /* Do this on entry only */
/* For these, don't even getregs */
if (pass == PTP_NOTHING || pass == PTP_DONE)
return;
ptrace(PTRACE_GETREGS, testpid, NULL, ®s);
if (regs.orig_rax != regs.rbx) {
fail("orig_rax %#llx doesn't match syscall number %#llx\n",
(unsigned long long)regs.orig_rax,
(unsigned long long)regs.rbx);
}
switch (pass) {
case PTP_GETREGS:
/* Just read, no writeback */
return;
case PTP_WRITEBACK:
/* Write back the same register state verbatim */
break;
case PTP_FUZZRET:
regs.rax = MODIFIED_BY_PTRACE;
break;
case PTP_FUZZHIGH:
regs.rax = MODIFIED_BY_PTRACE;
regs.orig_rax = regs.orig_rax | 0xffffffff00000000ULL;
break;
case PTP_INTNUM:
regs.rax = MODIFIED_BY_PTRACE;
regs.orig_rax = (int)regs.orig_rax;
break;
default:
crit("invalid ptrace_pass\n");
break;
}
ptrace(PTRACE_SETREGS, testpid, NULL, ®s);
}
static void syscall_numbering_tracer(pid_t testpid)
{
int wstatus;
do {
pid_t wpid = waitpid(testpid, &wstatus, 0);
if (wpid < 0 && errno != EINTR)
break;
if (wpid != testpid)
continue;
if (!WIFSTOPPED(wstatus))
break; /* Thread exited? */
if (sh->probing_syscall && WSTOPSIG(wstatus) == SIGTRAP)
mess_with_syscall(testpid, sh->ptrace_pass);
} while (sh->ptrace_pass != PTP_DONE &&
!ptrace(PTRACE_SYSCALL, testpid, NULL, NULL));
ptrace(PTRACE_DETACH, testpid, NULL, NULL);
/* Wait for the child process to terminate */
while (waitpid(testpid, &wstatus, 0) != testpid || !WIFEXITED(wstatus))
/* wait some more */;
}
static void test_traced_syscall_numbering(void)
{
pid_t testpid;
/* Launch the test thread; this thread continues as the tracer thread */
testpid = fork();
if (testpid < 0) {
crit("Unable to launch tracer process\n");
} else if (testpid == 0) {
syscall_numbering_tracee();
_exit(0);
} else {
syscall_numbering_tracer(testpid);
}
}
int main(void)
{
unsigned int nerr;
/*
* It is quite likely to get a segfault on a failure, so make
* sure the message gets out by setting stdout to nonbuffered.
*/
setvbuf(stdout, NULL, _IONBF, 0);
/*
* Harmless file descriptor to work on...
*/
nullfd = open("/dev/null", O_RDWR);
if (nullfd < 0) {
crit("Unable to open /dev/null: %s\n", strerror(errno));
}
/*
* Set up a block of shared memory...
*/
sh = mmap(NULL, sysconf(_SC_PAGE_SIZE), PROT_READ|PROT_WRITE,
MAP_ANONYMOUS|MAP_SHARED, 0, 0);
if (sh == MAP_FAILED) {
crit("Unable to allocated shared memory block: %s\n",
strerror(errno));
}
with_x32 = test_x32();
run("Running tests without ptrace...\n");
test_syscall_numbering();
test_traced_syscall_numbering();
nerr = sh->nerr;
if (!nerr) {
ok("All system calls succeeded or failed as expected\n");
return 0;
} else {
fail("A total of %u system call%s had incorrect behavior\n",
nerr, nerr != 1 ? "s" : "");
return 1;
}
}
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