proc: test how it holds up with mapping'less process

Create process without mappings and check

/proc/*/maps
/proc/*/numa_maps
/proc/*/smaps
/proc/*/smaps_rollup

They must be empty (excluding vsyscall page) or full of zeroes.

Retroactively this test should've caught embarassing /proc/*/smaps_rollup
oops:

[17752.703567] BUG: kernel NULL pointer dereference, address: 0000000000000000
[17752.703580] #PF: supervisor read access in kernel mode
[17752.703583] #PF: error_code(0x0000) - not-present page
[17752.703587] PGD 0 P4D 0
[17752.703593] Oops: 0000 [#1] PREEMPT SMP PTI
[17752.703598] CPU: 0 PID: 60649 Comm: cat Tainted: G W 5.19.9-100.fc35.x86_64 #1
[17752.703603] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./X99 Extreme6/3.1, BIOS P3.30 08/05/2016
[17752.703607] RIP: 0010:show_smaps_rollup+0x159/0x2e0

Note 1:
ProtectionKey field in /proc/*/smaps is optional,
so check most of its contents, not everything.

Note 2:
due to the nature of this test, child process hardly can signal
its readiness (after unmapping everything!) to parent.
I feel like "sleep(1)" is justified.
If you know how to do it without sleep please tell me.

Note 3:
/proc/*/statm is not tested but can be.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Alexey Dobriyan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/proc/.gitignore

···
 /proc-fsconfig-hidepid
 /proc-loadavg-001
 /proc-multiple-procfs
+/proc-empty-vm
 /proc-pid-vm
 /proc-self-map-files-001
 /proc-self-map-files-002

tools/testing/selftests/proc/Makefile

···
 TEST_GEN_PROGS += fd-002-posix-eq
 TEST_GEN_PROGS += fd-003-kthread
 TEST_GEN_PROGS += proc-loadavg-001
+TEST_GEN_PROGS += proc-empty-vm
 TEST_GEN_PROGS += proc-pid-vm
 TEST_GEN_PROGS += proc-self-map-files-001
 TEST_GEN_PROGS += proc-self-map-files-002

tools/testing/selftests/proc/proc-empty-vm.c

···
+/*
+ * Copyright (c) 2022 Alexey Dobriyan <[e-mail]>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Create a process without mappings by unmapping everything at once and
+ * holding it with ptrace(2). See what happens to
+ *
+ *	/proc/${pid}/maps
+ *	/proc/${pid}/numa_maps
+ *	/proc/${pid}/smaps
+ *	/proc/${pid}/smaps_rollup
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/resource.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+/*
+ * 0: vsyscall VMA doesn't exist	vsyscall=none
+ * 1: vsyscall VMA is --xp		vsyscall=xonly
+ * 2: vsyscall VMA is r-xp		vsyscall=emulate
+ */
+static int g_vsyscall;
+static const char *g_proc_pid_maps_vsyscall;
+static const char *g_proc_pid_smaps_vsyscall;
+
+static const char proc_pid_maps_vsyscall_0[] = "";
+static const char proc_pid_maps_vsyscall_1[] =
+"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n";
+static const char proc_pid_maps_vsyscall_2[] =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n";
+
+static const char proc_pid_smaps_vsyscall_0[] = "";
+
+static const char proc_pid_smaps_vsyscall_1[] =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n"
+"Size:                  4 kB\n"
+"KernelPageSize:        4 kB\n"
+"MMUPageSize:           4 kB\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+"THPeligible:    0\n"
+/*
+ * "ProtectionKey:" field is conditional. It is possible to check it as well,
+ * but I don't have such machine.
+ */
+;
+
+static const char proc_pid_smaps_vsyscall_2[] =
+"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n"
+"Size:                  4 kB\n"
+"KernelPageSize:        4 kB\n"
+"MMUPageSize:           4 kB\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+"THPeligible:    0\n"
+/*
+ * "ProtectionKey:" field is conditional. It is possible to check it as well,
+ * but I'm too tired.
+ */
+;
+
+static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
+{
+	_exit(EXIT_FAILURE);
+}
+
+static void sigaction_SIGSEGV_vsyscall(int _, siginfo_t *__, void *___)
+{
+	_exit(g_vsyscall);
+}
+
+/*
+ * vsyscall page can't be unmapped, probe it directly.
+ */
+static void vsyscall(void)
+{
+	pid_t pid;
+	int wstatus;
+
+	pid = fork();
+	if (pid < 0) {
+		fprintf(stderr, "fork, errno %d\n", errno);
+		exit(1);
+	}
+	if (pid == 0) {
+		setrlimit(RLIMIT_CORE, &(struct rlimit){});
+
+		/* Hide "segfault at ffffffffff600000" messages. */
+		struct sigaction act = {};
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV_vsyscall;
+		sigaction(SIGSEGV, &act, NULL);
+
+		g_vsyscall = 0;
+		/* gettimeofday(NULL, NULL); */
+		asm volatile (
+			"call %P0"
+			:
+			: "i" (0xffffffffff600000), "D" (NULL), "S" (NULL)
+			: "rax", "rcx", "r11"
+		);
+
+		g_vsyscall = 1;
+		*(volatile int *)0xffffffffff600000UL;
+
+		g_vsyscall = 2;
+		exit(g_vsyscall);
+	}
+	waitpid(pid, &wstatus, 0);
+	if (WIFEXITED(wstatus)) {
+		g_vsyscall = WEXITSTATUS(wstatus);
+	} else {
+		fprintf(stderr, "error: vsyscall wstatus %08x\n", wstatus);
+		exit(1);
+	}
+}
+
+static int test_proc_pid_maps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/maps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		perror("open /proc/${pid}/maps");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		if (g_vsyscall == 0) {
+			assert(rv == 0);
+		} else {
+			size_t len = strlen(g_proc_pid_maps_vsyscall);
+			assert(rv == len);
+			assert(memcmp(buf, g_proc_pid_maps_vsyscall, len) == 0);
+		}
+		return EXIT_SUCCESS;
+	}
+}
+
+static int test_proc_pid_numa_maps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/numa_maps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/numa_maps is under CONFIG_NUMA,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/numa_maps");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		assert(rv == 0);
+		return EXIT_SUCCESS;
+	}
+}
+
+static int test_proc_pid_smaps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/smaps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/smaps is under CONFIG_PROC_PAGE_MONITOR,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/smaps");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		if (g_vsyscall == 0) {
+			assert(rv == 0);
+		} else {
+			size_t len = strlen(g_proc_pid_maps_vsyscall);
+			/* TODO "ProtectionKey:" */
+			assert(rv > len);
+			assert(memcmp(buf, g_proc_pid_maps_vsyscall, len) == 0);
+		}
+		return EXIT_SUCCESS;
+	}
+}
+
+static const char g_smaps_rollup[] =
+"00000000-00000000 ---p 00000000 00:00 0                                  [rollup]\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Pss_Anon:              0 kB\n"
+"Pss_File:              0 kB\n"
+"Pss_Shmem:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+;
+
+static int test_proc_pid_smaps_rollup(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/smaps_rollup", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/smaps_rollup is under CONFIG_PROC_PAGE_MONITOR,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/smaps_rollup");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		assert(rv == sizeof(g_smaps_rollup) - 1);
+		assert(memcmp(buf, g_smaps_rollup, sizeof(g_smaps_rollup) - 1) == 0);
+		return EXIT_SUCCESS;
+	}
+}
+
+int main(void)
+{
+	int rv = EXIT_SUCCESS;
+
+	vsyscall();
+
+	switch (g_vsyscall) {
+	case 0:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_0;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_0;
+		break;
+	case 1:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_1;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_1;
+		break;
+	case 2:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_2;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_2;
+		break;
+	default:
+		abort();
+	}
+
+	pid_t pid = fork();
+	if (pid == -1) {
+		perror("fork");
+		return EXIT_FAILURE;
+	} else if (pid == 0) {
+		rv = ptrace(PTRACE_TRACEME, 0, NULL, NULL);
+		if (rv != 0) {
+			if (errno == EPERM) {
+				fprintf(stderr,
+"Did you know? ptrace(PTRACE_TRACEME) doesn't work under strace.\n"
+				);
+				kill(getppid(), SIGTERM);
+				return EXIT_FAILURE;
+			}
+			perror("ptrace PTRACE_TRACEME");
+			return EXIT_FAILURE;
+		}
+
+		/*
+		 * Hide "segfault at ..." messages. Signal handler won't run.
+		 */
+		struct sigaction act = {};
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV;
+		sigaction(SIGSEGV, &act, NULL);
+
+#ifdef __amd64__
+		munmap(NULL, ((size_t)1 << 47) - 4096);
+#else
+#error "implement 'unmap everything'"
+#endif
+		return EXIT_FAILURE;
+	} else {
+		/*
+		 * TODO find reliable way to signal parent that munmap(2) completed.
+		 * Child can't do it directly because it effectively doesn't exist
+		 * anymore. Looking at child's VM files isn't 100% reliable either:
+		 * due to a bug they may not become empty or empty-like.
+		 */
+		sleep(1);
+
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_maps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_numa_maps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_smaps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_smaps_rollup(pid);
+		}
+		/*
+		 * TODO test /proc/${pid}/statm, task_statm()
+		 * ->start_code, ->end_code aren't updated by munmap().
+		 * Output can be "0 0 0 2 0 0 0\n" where "2" can be anything.
+		 */
+
+		/* Cut the rope. */
+		int wstatus;
+		waitpid(pid, &wstatus, 0);
+		assert(WIFSTOPPED(wstatus));
+		assert(WSTOPSIG(wstatus) == SIGSEGV);
+	}
+
+	return rv;
+}