[PATCH 4/4] selftests/x86: Add tests for User-Mode Instruction Prevention

[Ricardo Neri]

Certain user space programs that run on virtual-8086 mode may utilize
instructions protected by the User-Mode Instruction Prevention (UMIP)
security feature present in new Intel processors: SGDT, SIDT and SMSW. In
such a case, a general protection exception is issued if UMIP is enabled.

For the aforementioned reason, UMIP can be optionally disabled for virtual-
8086 tasks with the umip=novm86 kernel parameter. The purpose of this new
test is to verify whether the impacted instructions can be executed without
causing such #GP. If no #GP exceptions occur, we expect to exit virtual-
8086 mode from INT 0x80; provided umip=novm86 was used in the kernel
parameter.

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 | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c
index d075ea0..6efa6eb 100644
--- a/tools/testing/selftests/x86/entry_from_vm86.c
+++ b/tools/testing/selftests/x86/entry_from_vm86.c
@@ -95,6 +95,11 @@ asm (
 	"int3\n\t"
 	"vmcode_int80:\n\t"
 	"int $0x80\n\t"
+	"umip:\n\t"
+	"sgdt (2052)\n\t"
+	"sidt (2052)\n\t"
+	"smsw (2052)\n\t"
+	"int $0x80\n\t"
 	".size vmcode, . - vmcode\n\t"
 	"end_vmcode:\n\t"
 	".code32\n\t"
@@ -103,7 +108,7 @@ asm (
 
 extern unsigned char vmcode[], end_vmcode[];
 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
-	vmcode_sti[], vmcode_int3[], vmcode_int80[];
+	vmcode_sti[], vmcode_int3[], vmcode_int80[], umip[];
 
 /* Returns false if the test was skipped. */
 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
@@ -218,6 +223,9 @@ int main(void)
 	v86.regs.eax = (unsigned int)-1;
 	do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
 
+	/* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */
+	do_test(&v86, umip - vmcode, VM86_INTx, 0x80, "UMIP tests");
+
 	/* Execute a null pointer */
 	v86.regs.cs = 0;
 	v86.regs.ss = 0;
-- 
2.7.4