[PATCH V3 22/30] selftests/sgx: Add test for TCS page permission changes

Reinette Chatre
2022-04-04T22:02:55Z

Kernel should not allow permission changes on TCS pages. Add test to
confirm this behavior.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since V2:
- Update to use new struct name struct sgx_enclave_restrict_perm -> struct
sgx_enclave_restrict_permissions. (Jarkko)

Changes since V1:
- Adapt test to the kernel interface changes: the ioctl() name change
and providing entire secinfo as parameter.
- Rewrite error path to reduce line lengths.

tools/testing/selftests/sgx/main.c | 74 ++++++++++++++++++++++++++++++
1 file changed, 74 insertions(+)

diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index 0e0bd1c4d702..59573c1128c8 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -121,6 +121,24 @@ static Elf64_Sym *vdso_symtab_get(struct vdso_symtab *symtab, const char *name)
return NULL;
}

+/*
+ * Return the offset in the enclave where the TCS segment can be found.
+ * The first RW segment loaded is the TCS.
+ */
+static off_t encl_get_tcs_offset(struct encl *encl)
+{
+ int i;
+
+ for (i = 0; i < encl->nr_segments; i++) {
+ struct encl_segment *seg = &encl->segment_tbl[i];
+
+ if (i == 0 && seg->prot == (PROT_READ | PROT_WRITE))
+ return seg->offset;
+ }
+
+ return -1;
+}
+
/*
* Return the offset in the enclave where the data segment can be found.
* The first RW segment loaded is the TCS, skip that to get info on the
@@ -567,6 +585,62 @@ TEST_F(enclave, pte_permissions)
EXPECT_EQ(self->run.exception_addr, 0);
}

+/*
+ * Modifying permissions of TCS page should not be possible.
+ */
+TEST_F(enclave, tcs_permissions)
+{
+ struct sgx_enclave_restrict_permissions ioc;
+ struct sgx_secinfo secinfo;
+ int ret, errno_save;
+
+ ASSERT_TRUE(setup_test_encl(ENCL_HEAP_SIZE_DEFAULT, &self->encl, _metadata));
+
+ memset(&self->run, 0, sizeof(self->run));
+ self->run.tcs = self->encl.encl_base;
+
+ memset(&ioc, 0, sizeof(ioc));
+ memset(&secinfo, 0, sizeof(secinfo));
+
+ /*
+ * Ensure kernel supports needed ioctl() and system supports needed
+ * commands.
+ */
+
+ ret = ioctl(self->encl.fd, SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS, &ioc);
+ errno_save = ret == -1 ? errno : 0;
+
+ /*
+ * Invalid parameters were provided during sanity check,
+ * expect command to fail.
+ */
+ ASSERT_EQ(ret, -1);
+
+ /* ret == -1 */
+ if (errno_save == ENOTTY)
+ SKIP(return,
+ "Kernel does not support SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS ioctl()");
+ else if (errno_save == ENODEV)
+ SKIP(return, "System does not support SGX2");
+
+ /*
+ * Attempt to make TCS page read-only. This is not allowed and
+ * should be prevented by the kernel.
+ */
+ secinfo.flags = PROT_READ;
+ ioc.offset = encl_get_tcs_offset(&self->encl);
+ ioc.length = PAGE_SIZE;
+ ioc.secinfo = (unsigned long)&secinfo;
+
+ ret = ioctl(self->encl.fd, SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS, &ioc);
+ errno_save = ret == -1 ? errno : 0;
+
+ EXPECT_EQ(ret, -1);
+ EXPECT_EQ(errno_save, EINVAL);
+ EXPECT_EQ(ioc.result, 0);
+ EXPECT_EQ(ioc.count, 0);
+}
+
/*
* Enclave page permission test.
*
--
2.25.1