[PATCH v7 25/26] selftests/x86: Add tests for User-Mode Instruction Prevention

Ricardo Neri
2017-05-05T18:17:23Z

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 fault is issued if UMIP is enabled. When
such a fault happens, the kernel traps it and emulates the results of
these instructions with dummy values. 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 INT3.

The instructions protected by UMIP are executed in representative use
cases:
a) displacement-only memory addressing
b) register-indirect memory addressing
c) results stored directly in operands

Unfortunately, it is not possible to check the results against a set of
expected values because no emulation will occur in systems that do not
have the UMIP feature. Instead, results are printed for verification. A
simple verification is done to ensure that results of all tests are
identical.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chen Yucong <slaoub@gmail.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
tools/testing/selftests/x86/entry_from_vm86.c | 73 ++++++++++++++++++++++++++-
1 file changed, 72 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..130e8ad 100644
--- a/tools/testing/selftests/x86/entry_from_vm86.c
+++ b/tools/testing/selftests/x86/entry_from_vm86.c
@@ -95,6 +95,22 @@ asm (
"int3\n\t"
"vmcode_int80:\n\t"
"int $0x80\n\t"
+ "vmcode_umip:\n\t"
+ /* addressing via displacements */
+ "smsw (2052)\n\t"
+ "sidt (2054)\n\t"
+ "sgdt (2060)\n\t"
+ /* addressing via registers */
+ "mov $2066, %bx\n\t"
+ "smsw (%bx)\n\t"
+ "mov $2068, %bx\n\t"
+ "sidt (%bx)\n\t"
+ "mov $2074, %bx\n\t"
+ "sgdt (%bx)\n\t"
+ /* register operands, only for smsw */
+ "smsw %ax\n\t"
+ "mov %ax, (2080)\n\t"
+ "int3\n\t"
".size vmcode, . - vmcode\n\t"
"end_vmcode:\n\t"
".code32\n\t"
@@ -103,7 +119,7 @@ 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[], vmcode_umip[];

/* Returns false if the test was skipped. */
static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
@@ -160,6 +176,58 @@ static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
return true;
}

+void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem)
+{
+ struct table_desc {
+ unsigned short limit;
+ unsigned long base;
+ } __attribute__((packed));
+
+ /* Initialize variables with arbitrary values */
+ struct table_desc gdt1 = { .base = 0x3c3c3c3c, .limit = 0x9999 };
+ struct table_desc gdt2 = { .base = 0x1a1a1a1a, .limit = 0xaeae };
+ struct table_desc idt1 = { .base = 0x7b7b7b7b, .limit = 0xf1f1 };
+ struct table_desc idt2 = { .base = 0x89898989, .limit = 0x1313 };
+ unsigned short msw1 = 0x1414, msw2 = 0x2525, msw3 = 3737;
+
+ /* UMIP -- exit with INT3 unless kernel emulation did not trap #GP */
+ do_test(vm86, vmcode_umip - vmcode, VM86_TRAP, 3, "UMIP tests");
+
+ /* Results from displacement-only addressing */
+ msw1 = *(unsigned short *)(test_mem + 2052);
+ memcpy(&idt1, test_mem + 2054, sizeof(idt1));
+ memcpy(&gdt1, test_mem + 2060, sizeof(gdt1));
+
+ /* Results from register-indirect addressing */
+ msw2 = *(unsigned short *)(test_mem + 2066);
+ memcpy(&idt2, test_mem + 2068, sizeof(idt2));
+ memcpy(&gdt2, test_mem + 2074, sizeof(gdt2));
+
+ /* Results when using register operands */
+ msw3 = *(unsigned short *)(test_mem + 2080);
+
+ printf("[INFO]\tResult from SMSW:[0x%04x]\n", msw1);
+ printf("[INFO]\tResult from SIDT: limit[0x%04x]base[0x%08lx]\n",
+ idt1.limit, idt1.base);
+ printf("[INFO]\tResult from SGDT: limit[0x%04x]base[0x%08lx]\n",
+ gdt1.limit, gdt1.base);
+
+ if ((msw1 != msw2) || (msw1 != msw3))
+ printf("[FAIL]\tAll the results of SMSW should be the same.\n");
+ else
+ printf("[PASS]\tAll the results from SMSW are identical.\n");
+
+ if (memcmp(&gdt1, &gdt2, sizeof(gdt1)))
+ printf("[FAIL]\tAll the results of SGDT should be the same.\n");
+ else
+ printf("[PASS]\tAll the results from SGDT are identical.\n");
+
+ if (memcmp(&idt1, &idt2, sizeof(idt1)))
+ printf("[FAIL]\tAll the results of SIDT should be the same.\n");
+ else
+ printf("[PASS]\tAll the results from SIDT are identical.\n");
+}
+
int main(void)
{
struct vm86plus_struct v86;
@@ -218,6 +286,9 @@ 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_umip_tests(&v86, addr);
+
/* Execute a null pointer */
v86.regs.cs = 0;
v86.regs.ss = 0;
--
2.9.3