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Subject[PATCH v4.1 3.3] selftests/x86, x86/ldt: Add a selftest for modify_ldt
Date
This tests general modify_ldt behavior (only writes, so far) as
well as synchronous updates via IPI. It fails on old kernels.

I called this ldt_gdt because I'll add set_thread_area tests to
it at some point.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---

Oops. This is what I meant to send as v4. Patches 1 and 2 were correct
but I sent the wrong version of patch 3.

tools/testing/selftests/x86/Makefile | 2 +-
tools/testing/selftests/x86/ldt_gdt.c | 520 ++++++++++++++++++++++++++++++++++
2 files changed, 521 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/x86/ldt_gdt.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index caa60d56d7d1..4138387b892c 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -4,7 +4,7 @@ include ../lib.mk

.PHONY: all all_32 all_64 warn_32bit_failure clean

-TARGETS_C_BOTHBITS := sigreturn single_step_syscall sysret_ss_attrs
+TARGETS_C_BOTHBITS := sigreturn single_step_syscall sysret_ss_attrs ldt_gdt
TARGETS_C_32BIT_ONLY := entry_from_vm86

TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c
new file mode 100644
index 000000000000..c27adfc9ae72
--- /dev/null
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -0,0 +1,520 @@
+/*
+ * ldt_gdt.c - Test cases for LDT and GDT access
+ * Copyright (c) 2015 Andrew Lutomirski
+ */
+
+#define _GNU_SOURCE
+#include <err.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <signal.h>
+#include <setjmp.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <asm/ldt.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <stdbool.h>
+#include <pthread.h>
+#include <sched.h>
+#include <linux/futex.h>
+
+#define AR_ACCESSED (1<<8)
+
+#define AR_TYPE_RODATA (0 * (1<<9))
+#define AR_TYPE_RWDATA (1 * (1<<9))
+#define AR_TYPE_RODATA_EXPDOWN (2 * (1<<9))
+#define AR_TYPE_RWDATA_EXPDOWN (3 * (1<<9))
+#define AR_TYPE_XOCODE (4 * (1<<9))
+#define AR_TYPE_XRCODE (5 * (1<<9))
+#define AR_TYPE_XOCODE_CONF (6 * (1<<9))
+#define AR_TYPE_XRCODE_CONF (7 * (1<<9))
+
+#define AR_DPL3 (3 * (1<<13))
+
+#define AR_S (1 << 12)
+#define AR_P (1 << 15)
+#define AR_AVL (1 << 20)
+#define AR_L (1 << 21)
+#define AR_DB (1 << 22)
+#define AR_G (1 << 23)
+
+static int nerrs;
+
+static void check_invalid_segment(uint16_t index, int ldt)
+{
+ uint32_t has_limit = 0, has_ar = 0, limit, ar;
+ uint32_t selector = (index << 3) | (ldt << 2) | 3;
+
+ asm ("lsl %[selector], %[limit]\n\t"
+ "jnz 1f\n\t"
+ "movl $1, %[has_limit]\n\t"
+ "1:"
+ : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
+ : [selector] "r" (selector));
+ asm ("larl %[selector], %[ar]\n\t"
+ "jnz 1f\n\t"
+ "movl $1, %[has_ar]\n\t"
+ "1:"
+ : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
+ : [selector] "r" (selector));
+
+ if (has_limit || has_ar) {
+ printf("[FAIL]\t%s entry %hu is valid but should be invalid\n",
+ (ldt ? "LDT" : "GDT"), index);
+ nerrs++;
+ } else {
+ printf("[OK]\t%s entry %hu is invalid\n",
+ (ldt ? "LDT" : "GDT"), index);
+ }
+}
+
+static void check_valid_segment(uint16_t index, int ldt,
+ uint32_t expected_ar, uint32_t expected_limit,
+ bool verbose)
+{
+ uint32_t has_limit = 0, has_ar = 0, limit, ar;
+ uint32_t selector = (index << 3) | (ldt << 2) | 3;
+
+ asm ("lsl %[selector], %[limit]\n\t"
+ "jnz 1f\n\t"
+ "movl $1, %[has_limit]\n\t"
+ "1:"
+ : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
+ : [selector] "r" (selector));
+ asm ("larl %[selector], %[ar]\n\t"
+ "jnz 1f\n\t"
+ "movl $1, %[has_ar]\n\t"
+ "1:"
+ : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
+ : [selector] "r" (selector));
+
+ if (!has_limit || !has_ar) {
+ printf("[FAIL]\t%s entry %hu is invalid but should be valid\n",
+ (ldt ? "LDT" : "GDT"), index);
+ nerrs++;
+ return;
+ }
+
+ if (ar != expected_ar) {
+ printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
+ (ldt ? "LDT" : "GDT"), index, ar, expected_ar);
+ nerrs++;
+ } else if (limit != expected_limit) {
+ printf("[FAIL]\t%s entry %hu has limit 0x%08X but expected 0x%08X\n",
+ (ldt ? "LDT" : "GDT"), index, limit, expected_limit);
+ nerrs++;
+ } else if (verbose) {
+ printf("[OK]\t%s entry %hu has AR 0x%08X and limit 0x%08X\n",
+ (ldt ? "LDT" : "GDT"), index, ar, limit);
+ }
+}
+
+static bool install_valid_mode(const struct user_desc *desc, uint32_t ar,
+ bool oldmode)
+{
+ int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
+ desc, sizeof(*desc));
+ if (ret < -1)
+ errno = -ret;
+ if (ret == 0) {
+ uint32_t limit = desc->limit;
+ if (desc->limit_in_pages)
+ limit = (limit << 12) + 4095;
+ check_valid_segment(desc->entry_number, 1, ar, limit, true);
+ return true;
+ } else if (errno == ENOSYS) {
+ printf("[OK]\tmodify_ldt returned -ENOSYS\n");
+ return false;
+ } else {
+ if (desc->seg_32bit) {
+ printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
+ errno);
+ nerrs++;
+ return false;
+ } else {
+ printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
+ return false;
+ }
+ }
+}
+
+static bool install_valid(const struct user_desc *desc, uint32_t ar)
+{
+ return install_valid_mode(desc, ar, false);
+}
+
+static void install_invalid(const struct user_desc *desc, bool oldmode)
+{
+ int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
+ desc, sizeof(*desc));
+ if (ret < -1)
+ errno = -ret;
+ if (ret == 0) {
+ check_invalid_segment(desc->entry_number, 1);
+ } else if (errno == ENOSYS) {
+ printf("[OK]\tmodify_ldt returned -ENOSYS\n");
+ } else {
+ if (desc->seg_32bit) {
+ printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
+ errno);
+ nerrs++;
+ } else {
+ printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
+ }
+ }
+}
+
+static int safe_modify_ldt(int func, struct user_desc *ptr,
+ unsigned long bytecount)
+{
+ int ret = syscall(SYS_modify_ldt, 0x11, ptr, bytecount);
+ if (ret < -1)
+ errno = -ret;
+ return ret;
+}
+
+static void fail_install(struct user_desc *desc)
+{
+ if (safe_modify_ldt(0x11, desc, sizeof(*desc)) == 0) {
+ printf("[FAIL]\tmodify_ldt accepted a bad descriptor\n");
+ nerrs++;
+ } else if (errno == ENOSYS) {
+ printf("[OK]\tmodify_ldt returned -ENOSYS\n");
+ } else {
+ printf("[OK]\tmodify_ldt failure %d\n", errno);
+ }
+}
+
+static void do_simple_tests(void)
+{
+ struct user_desc desc = {
+ .entry_number = 0,
+ .base_addr = 0,
+ .limit = 10,
+ .seg_32bit = 1,
+ .contents = 2, /* Code, not conforming */
+ .read_exec_only = 0,
+ .limit_in_pages = 0,
+ .seg_not_present = 0,
+ .useable = 0
+ };
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);
+
+ desc.limit_in_pages = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_P | AR_DB | AR_G);
+
+ check_invalid_segment(1, 1);
+
+ desc.entry_number = 2;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_P | AR_DB | AR_G);
+
+ check_invalid_segment(1, 1);
+
+ desc.base_addr = 0xf0000000;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_P | AR_DB | AR_G);
+
+ desc.useable = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_P | AR_DB | AR_G | AR_AVL);
+
+ desc.seg_not_present = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_DB | AR_G | AR_AVL);
+
+ desc.seg_32bit = 0;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_G | AR_AVL);
+
+ desc.seg_32bit = 1;
+ desc.contents = 0;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA |
+ AR_S | AR_DB | AR_G | AR_AVL);
+
+ desc.read_exec_only = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA |
+ AR_S | AR_DB | AR_G | AR_AVL);
+
+ desc.contents = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA_EXPDOWN |
+ AR_S | AR_DB | AR_G | AR_AVL);
+
+ desc.read_exec_only = 0;
+ desc.limit_in_pages = 0;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA_EXPDOWN |
+ AR_S | AR_DB | AR_AVL);
+
+ desc.contents = 3;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE_CONF |
+ AR_S | AR_DB | AR_AVL);
+
+ desc.read_exec_only = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE_CONF |
+ AR_S | AR_DB | AR_AVL);
+
+ desc.read_exec_only = 0;
+ desc.contents = 2;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
+ AR_S | AR_DB | AR_AVL);
+
+ desc.read_exec_only = 1;
+
+#ifdef __x86_64__
+ desc.lm = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
+ AR_S | AR_DB | AR_AVL);
+ desc.lm = 0;
+#endif
+
+ bool entry1_okay = install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
+ AR_S | AR_DB | AR_AVL);
+
+ if (entry1_okay) {
+ printf("[RUN]\tTest fork\n");
+ pid_t child = fork();
+ if (child == 0) {
+ nerrs = 0;
+ check_valid_segment(desc.entry_number, 1,
+ AR_DPL3 | AR_TYPE_XOCODE |
+ AR_S | AR_DB | AR_AVL, desc.limit,
+ true);
+ check_invalid_segment(1, 1);
+ exit(nerrs ? 1 : 0);
+ } else {
+ int status;
+ if (waitpid(child, &status, 0) != child ||
+ !WIFEXITED(status)) {
+ printf("[FAIL]\tChild died\n");
+ nerrs++;
+ } else if (WEXITSTATUS(status) != 0) {
+ printf("[FAIL]\tChild failed\n");
+ nerrs++;
+ } else {
+ printf("[OK]\tChild succeeded\n");
+ }
+ }
+
+ printf("[RUN]\tTest size\n");
+ int i;
+ for (i = 0; i < 8192; i++) {
+ desc.entry_number = i;
+ desc.limit = i;
+ if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
+ printf("[FAIL]\tFailed to install entry %d\n", i);
+ nerrs++;
+ break;
+ }
+ }
+ for (int j = 0; j < i; j++) {
+ check_valid_segment(j, 1, AR_DPL3 | AR_TYPE_XOCODE |
+ AR_S | AR_DB | AR_AVL, j, false);
+ }
+ printf("[DONE]\tSize test\n");
+ } else {
+ printf("[SKIP]\tSkipping fork and size tests because we have no LDT\n");
+ }
+
+ /* Test entry_number too high. */
+ desc.entry_number = 8192;
+ fail_install(&desc);
+
+ /* Test deletion and actions mistakeable for deletion. */
+ memset(&desc, 0, sizeof(desc));
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P);
+
+ desc.seg_not_present = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
+
+ desc.seg_not_present = 0;
+ desc.read_exec_only = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S | AR_P);
+
+ desc.read_exec_only = 0;
+ desc.seg_not_present = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
+
+ desc.read_exec_only = 1;
+ desc.limit = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
+
+ desc.limit = 0;
+ desc.base_addr = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
+
+ desc.base_addr = 0;
+ install_invalid(&desc, false);
+
+ desc.seg_not_present = 0;
+ desc.read_exec_only = 0;
+ desc.seg_32bit = 1;
+ install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB);
+ install_invalid(&desc, true);
+}
+
+/*
+ * 0: thread is idle
+ * 1: thread armed
+ * 2: thread should clear LDT entry 0
+ * 3: thread should exit
+ */
+static volatile unsigned int ftx;
+
+static void *threadproc(void *ctx)
+{
+ cpu_set_t cpuset;
+ CPU_ZERO(&cpuset);
+ CPU_SET(1, &cpuset);
+ if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
+ err(1, "sched_setaffinity to CPU 1"); /* should never fail */
+
+ while (1) {
+ syscall(SYS_futex, &ftx, FUTEX_WAIT, 0, NULL, NULL, 0);
+ while (ftx != 2) {
+ if (ftx >= 3)
+ return NULL;
+ }
+
+ /* clear LDT entry 0 */
+ const struct user_desc desc = {};
+ if (syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)) != 0)
+ err(1, "modify_ldt");
+
+ /* If ftx == 2, set it to zero. If ftx == 100, quit. */
+ unsigned int x = -2;
+ asm volatile ("lock xaddl %[x], %[ftx]" :
+ [x] "+r" (x), [ftx] "+m" (ftx));
+ if (x != 2)
+ return NULL;
+ }
+}
+
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+ int flags)
+{
+ struct sigaction sa;
+ memset(&sa, 0, sizeof(sa));
+ sa.sa_sigaction = handler;
+ sa.sa_flags = SA_SIGINFO | flags;
+ sigemptyset(&sa.sa_mask);
+ if (sigaction(sig, &sa, 0))
+ err(1, "sigaction");
+
+}
+
+static jmp_buf jmpbuf;
+
+static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
+{
+ siglongjmp(jmpbuf, 1);
+}
+
+static void do_multicpu_tests(void)
+{
+ cpu_set_t cpuset;
+ pthread_t thread;
+ int failures = 0, iters = 5, i;
+ unsigned short orig_ss;
+
+ CPU_ZERO(&cpuset);
+ CPU_SET(1, &cpuset);
+ if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
+ printf("[SKIP]\tCannot set affinity to CPU 1\n");
+ return;
+ }
+
+ CPU_ZERO(&cpuset);
+ CPU_SET(0, &cpuset);
+ if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
+ printf("[SKIP]\tCannot set affinity to CPU 0\n");
+ return;
+ }
+
+ sethandler(SIGSEGV, sigsegv, 0);
+#ifdef __i386__
+ /* True 32-bit kernels send SIGILL instead of SIGSEGV on IRET faults. */
+ sethandler(SIGILL, sigsegv, 0);
+#endif
+
+ printf("[RUN]\tCross-CPU LDT invalidation\n");
+
+ if (pthread_create(&thread, 0, threadproc, 0) != 0)
+ err(1, "pthread_create");
+
+ asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
+
+ for (i = 0; i < 5; i++) {
+ if (sigsetjmp(jmpbuf, 1) != 0)
+ continue;
+
+ /* Make sure the thread is ready after the last test. */
+ while (ftx != 0)
+ ;
+
+ struct user_desc desc = {
+ .entry_number = 0,
+ .base_addr = 0,
+ .limit = 0xfffff,
+ .seg_32bit = 1,
+ .contents = 0, /* Data */
+ .read_exec_only = 0,
+ .limit_in_pages = 1,
+ .seg_not_present = 0,
+ .useable = 0
+ };
+
+ if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
+ if (errno != ENOSYS)
+ err(1, "modify_ldt");
+ printf("[SKIP]\tmodify_ldt unavailable\n");
+ break;
+ }
+
+ /* Arm the thread. */
+ ftx = 1;
+ syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
+
+ asm volatile ("mov %0, %%ss" : : "r" (0x7));
+
+ /* Go! */
+ ftx = 2;
+
+ while (ftx != 0)
+ ;
+
+ /*
+ * On success, modify_ldt will segfault us synchronously,
+ * and we'll escape via siglongjmp.
+ */
+
+ failures++;
+ asm volatile ("mov %0, %%ss" : : "rm" (orig_ss));
+ };
+
+ ftx = 100; /* Kill the thread. */
+ syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
+
+ if (pthread_join(thread, NULL) != 0)
+ err(1, "pthread_join");
+
+ if (failures) {
+ printf("[FAIL]\t%d of %d iterations failed\n", failures, iters);
+ nerrs++;
+ } else {
+ printf("[OK]\tAll %d iterations succeeded\n", iters);
+ }
+}
+
+int main()
+{
+ do_simple_tests();
+
+ do_multicpu_tests();
+
+ return nerrs ? 1 : 0;
+}
--
2.4.3


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