sysret_ss_attrs: New test, WIP

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

2 files changed, 68 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 1447ecf..5afc43a 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ SIMPLE_C_TARGETS := dump-vsyscall context_switch_latency kernel_pf user_visible_
 
 SIMPLE_CC_TARGETS := evil-clock-test
 
-SPLIT_C_TARGETS := dump-vdso dump-vvar syscall_exit_regs dump_all_pmcs ntflag
+SPLIT_C_TARGETS := dump-vdso dump-vvar syscall_exit_regs dump_all_pmcs ntflag sysret_ss_attrs
 SPLIT_CC_TARGETS := timing_test test_vsyscall test_vdso_parser
 
 ALL_TARGETS := $(SIMPLE_C_TARGETS) $(SIMPLE_CC_TARGETS) $(SPLIT_C_TARGETS:%=%_64) $(SPLIT_CC_TARGETS:%=%_64) $(SPLIT_C_TARGETS:%=%_32) $(SPLIT_CC_TARGETS:%=%_32) syscall32_from_64 segregs
diff --git a/sysret_ss_attrs.c b/sysret_ss_attrs.c
new file mode 100644
index 0000000..fa81ce2
--- /dev/null
+++ b/sysret_ss_attrs.c
@@ -0,0 +1,67 @@
+#define _GNU_SOURCE
+
+#include <sys/time.h>
+#include <time.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <sys/mman.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <asm/ldt.h>
+#include <err.h>
+#include <setjmp.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <sys/ptrace.h>
+#include <sys/user.h>
+#include <pthread.h>
+
+static unsigned short GDT3(int idx)
+{
+	return (idx << 3) | 3;
+}
+
+static void *threadproc(void *ctx)
+{
+	struct user_desc desc = {
+		.entry_number    = -1,
+		.base_addr       = 0,
+		.limit           = 1,
+		.seg_32bit       = 1,
+		.contents        = 0, /* Data, grow-up */
+		.read_exec_only  = 0,
+		.limit_in_pages  = 0,
+		.seg_not_present = 0,
+		.useable         = 0,
+	};
+
+	if (syscall(SYS_set_thread_area, &desc) != 0)
+		err(1, "set_thread_area");
+
+	asm volatile (
+		"mov %%ax, %%ss\n\t"
+		"1:\n\t"
+		"movl $0xbfffffff, %%eax\n\t"
+		"int $0x80\n\t"
+		"jmp 1b"
+		: : "a" (GDT3(desc.entry_number))
+		);
+	return NULL;
+}
+
+int main()
+{
+	pthread_t thread;
+	if (pthread_create(&thread, 0, threadproc, 0) != 0)
+		err(1, "pthread_create");
+
+	while (1) {
+		usleep(1);
+	}
+
+	return 0;
+}