[PATCH v8 28/28] selftests/x86: Add tests for instruction str and sldt

[Ricardo Neri]

The instructions str and sldt are not recognized when running on virtual-
8086 mode and generate an invalid operand exception. These two
instructions are protected by the Intel User-Mode Instruction Prevention
(UMIP) security feature. In protected mode, if UMIP is enabled, these
instructions generate a general protection fault if called from CPL > 0.
Linux traps the general protection fault and emulates the instructions
sgdt, sidt and smsw; but not str and sldt.

These tests are added to verify that the emulation code does not emulate
these two instructions but the expected invalid operand exception is
seen.

Tests fallback to exit with int3 in case emulation does happen.

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Chen Yucong <slaoub@xxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 tools/testing/selftests/x86/entry_from_vm86.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c
index 130e8ad1db05..b7a0c9024477 100644
--- a/tools/testing/selftests/x86/entry_from_vm86.c
+++ b/tools/testing/selftests/x86/entry_from_vm86.c
@@ -111,6 +111,11 @@ asm (
 	"smsw %ax\n\t"
 	"mov %ax, (2080)\n\t"
 	"int3\n\t"
+	"vmcode_umip_str:\n\t"
+	"str %eax\n\t"
+	"vmcode_umip_sldt:\n\t"
+	"sldt %eax\n\t"
+	"int3\n\t"
 	".size vmcode, . - vmcode\n\t"
 	"end_vmcode:\n\t"
 	".code32\n\t"
@@ -119,7 +124,8 @@ asm (
 
 extern unsigned char vmcode[], end_vmcode[];
 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
-	vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[];
+	vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[],
+	vmcode_umip_str[], vmcode_umip_sldt[];
 
 /* Returns false if the test was skipped. */
 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
@@ -226,6 +232,16 @@ void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem)
 		printf("[FAIL]\tAll the results of SIDT should be the same.\n");
 	else
 		printf("[PASS]\tAll the results from SIDT are identical.\n");
+
+	sethandler(SIGILL, sighandler, 0);
+	do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0,
+		"STR instruction");
+	clearhandler(SIGILL);
+
+	sethandler(SIGILL, sighandler, 0);
+	do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0,
+		"SLDT instruction");
+	clearhandler(SIGILL);
 }
 
 int main(void)
-- 
2.13.0