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[Xen-devel] [PATCH v3 3/3] selftests/x86, x86/ldt: Add a selftest for modify_ldt



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@xxxxxxxxxx>
---
 tools/testing/selftests/x86/Makefile  |   2 +-
 tools/testing/selftests/x86/ldt_gdt.c | 492 ++++++++++++++++++++++++++++++++++
 2 files changed, 493 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..7723a12d42e1
--- /dev/null
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -0,0 +1,492 @@
+/*
+ * 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)
+{
+       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 {
+               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);
+               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);
+                       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");
+                       }
+               }
+       } else {
+               printf("[SKIP]\tSkipping fork test because have no LDT\n");
+       }
+
+       /* Test entry_number too high. */
+       desc.entry_number = 100000;
+       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");
+
+               ftx = 0;
+       }
+}
+
+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);
+
+       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 = 3;
+       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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