From: Peter Zijlstra <peterz@infradead.org>

do_ldt_ss_test() - tests modifying the SS segment while in use; this
tends to come apart with RO LDT maps

do_ldt_unmap_test() - tests the mechanics of unmapping the (future)
LDT VMA. Additional tests would make sense; like unmapping it while in
use (TODO).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 tools/testing/selftests/x86/ldt_gdt.c |   71 +++++++++++++++++++++++++++++++++-
 1 file changed, 70 insertions(+), 1 deletion(-)

--- a/tools/testing/selftests/x86/ldt_gdt.c
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -242,6 +242,72 @@ static void fail_install(struct user_des
 	}
 }
 
+static void do_ldt_ss_test(void)
+{
+	unsigned short prev_sel, sel = (2 << 3) | (1 << 2) | 3;
+	struct user_desc *ldt_desc = low_user_desc + 2;
+	int ret;
+
+	ldt_desc->entry_number	= 2;
+	ldt_desc->base_addr	= (unsigned long)&counter_page[1];
+	ldt_desc->limit		= 0xfffff;
+	ldt_desc->seg_32bit	= 1;
+	ldt_desc->contents		= 0; /* Data, grow-up*/
+	ldt_desc->read_exec_only	= 0;
+	ldt_desc->limit_in_pages	= 1;
+	ldt_desc->seg_not_present	= 0;
+	ldt_desc->useable		= 0;
+
+	ret = safe_modify_ldt(1, ldt_desc, sizeof(*ldt_desc));
+	if (ret)
+		perror("ponies");
+
+	/*
+	 * syscall (eax) 123 - modify_ldt / return value
+	 *         (ebx)     - func
+	 *         (ecx)     - ptr
+	 *         (edx)     - bytecount
+	 */
+
+	int eax = 123;
+	int ebx = 1;
+	int ecx = (unsigned int)(unsigned long)ldt_desc;
+	int edx = sizeof(struct user_desc);
+
+	asm volatile ("movw %%ss, %[prev_sel]\n\t"
+		      "movw %[sel], %%ss\n\t"
+		      "int $0x80\n\t"
+		      "movw %[prev_sel], %%ss"
+		      : [prev_sel] "=&R" (prev_sel), "+a" (eax)
+		      : [sel] "R" (sel), "b" (ebx), "c" (ecx), "d" (edx)
+		      : INT80_CLOBBERS);
+
+	printf("[OK]\tSS modify_ldt()\n");
+}
+
+static void do_ldt_unmap_test(void)
+{
+	FILE *file = fopen("/proc/self/maps", "r");
+	char *line = NULL;
+	size_t len = 0;
+	ssize_t nread;
+	unsigned long start, end;
+
+	while ((nread = getline(&line, &len, file)) != -1) {
+		if (strstr(line, "[ldt]")) {
+			if (sscanf(line, "%lx-%lx", &start, &end) == 2) {
+				munmap((void *)start, end-start);
+				printf("[OK]\tmunmap LDT\n");
+				break;
+			}
+		}
+	}
+
+	free(line);
+	fclose(file);
+
+}
+
 static void do_simple_tests(void)
 {
 	struct user_desc desc = {
@@ -696,7 +762,7 @@ static int invoke_set_thread_area(void)
 
 static void setup_low_user_desc(void)
 {
-	low_user_desc = mmap(NULL, 2 * sizeof(struct user_desc),
+	low_user_desc = mmap(NULL, 3 * sizeof(struct user_desc),
 			     PROT_READ | PROT_WRITE,
 			     MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1, 0);
 	if (low_user_desc == MAP_FAILED)
@@ -916,6 +982,9 @@ int main(int argc, char **argv)
 	setup_counter_page();
 	setup_low_user_desc();
 
+	do_ldt_ss_test();
+	do_ldt_unmap_test();
+
 	do_simple_tests();
 
 	do_multicpu_tests();