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Date: Wed, 5 Oct 2022 23:14:00 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] 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.
Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
tools/testing/selftests/proc/.gitignore | 1
tools/testing/selftests/proc/Makefile | 1
tools/testing/selftests/proc/proc-empty-vm.c | 386 +++++++++++++++++++++++++++
3 files changed, 388 insertions(+)
--- a/tools/testing/selftests/proc/.gitignore
+++ b/tools/testing/selftests/proc/.gitignore
@@ -5,6 +5,7 @@
/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
--- a/tools/testing/selftests/proc/Makefile
+++ b/tools/testing/selftests/proc/Makefile
@@ -8,6 +8,7 @@ TEST_GEN_PROGS += fd-001-lookup
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
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-empty-vm.c
@@ -0,0 +1,386 @@
+/*
+ * Copyright (c) 2022 Alexey Dobriyan <adobriyan@...il.com>
+ *
+ * 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;
+}
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