[PATCH V2 21/32] selftests/sgx: Test two different SGX2 EAUG flows

Reinette Chatre
2022-02-08T01:07:03Z

Enclave pages can be added to an initialized enclave when an address
belonging to the enclave but without a backing page is accessed from
within the enclave.

Accessing memory without a backing enclave page from within an enclave
can be in different ways:
1) Pre-emptively run ENCLU[EACCEPT]. Since the addition of a page
always needs to be accepted by the enclave via ENCLU[EACCEPT] this
flow is efficient since the first execution of ENCLU[EACCEPT]
triggers the addition of the page and when execution returns to the
same instruction the second execution would be successful as an
acceptance of the page.

2) A direct read or write. The flow where a direct read or write
triggers the page addition execution cannot resume from the
instruction (read/write) that triggered the fault but instead
the enclave needs to be entered at a different entry point to
run needed ENCLU[EACCEPT] before execution can return to the
original entry point and the read/write instruction that faulted.

Add tests for both flows.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since v1:
- Replace __cpuid() definition and usage with __cpuid_count().
- Fix accuracy of comments.

tools/testing/selftests/sgx/main.c | 243 +++++++++++++++++++++++++++++
1 file changed, 243 insertions(+)

diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index 1398cd1b0983..68285603b3f0 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -86,6 +86,15 @@ static bool vdso_get_symtab(void *addr, struct vdso_symtab *symtab)
return true;
}

+static inline int sgx2_supported(void)
+{
+ unsigned int eax, ebx, ecx, edx;
+
+ __cpuid_count(SGX_CPUID, 0x0, eax, ebx, ecx, edx);
+
+ return eax & 0x2;
+}
+
static unsigned long elf_sym_hash(const char *name)
{
unsigned long h = 0, high;
@@ -882,4 +891,238 @@ TEST_F(enclave, epcm_permissions)
EXPECT_EQ(self->run.exception_addr, 0);
}

+/*
+ * Test the addition of pages to an initialized enclave via writing to
+ * a page belonging to the enclave's address space but was not added
+ * during enclave creation.
+ */
+TEST_F(enclave, augment)
+{
+ struct encl_op_get_from_addr get_addr_op;
+ struct encl_op_put_to_addr put_addr_op;
+ struct encl_op_eaccept eaccept_op;
+ size_t total_size = 0;
+ void *addr;
+ int i;
+
+ if (!sgx2_supported())
+ SKIP(return, "SGX2 not supported");
+
+ 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;
+
+ for (i = 0; i < self->encl.nr_segments; i++) {
+ struct encl_segment *seg = &self->encl.segment_tbl[i];
+
+ total_size += seg->size;
+ }
+
+ /*
+ * Actual enclave size is expected to be larger than the loaded
+ * test enclave since enclave size must be a power of 2 in bytes
+ * and test_encl does not consume it all.
+ */
+ EXPECT_LT(total_size + PAGE_SIZE, self->encl.encl_size);
+
+ /*
+ * Create memory mapping for the page that will be added. New
+ * memory mapping is for one page right after all existing
+ * mappings.
+ */
+ addr = mmap((void *)self->encl.encl_base + total_size, PAGE_SIZE,
+ PROT_READ | PROT_WRITE | PROT_EXEC,
+ MAP_SHARED | MAP_FIXED, self->encl.fd, 0);
+ EXPECT_NE(addr, MAP_FAILED);
+
+ self->run.exception_vector = 0;
+ self->run.exception_error_code = 0;
+ self->run.exception_addr = 0;
+
+ /*
+ * Attempt to write to the new page from within enclave.
+ * Expected to fail since page is not (yet) part of the enclave.
+ * The first #PF will trigger the addition of the page to the
+ * enclave, but since the new page needs an EACCEPT from within the
+ * enclave before it can be used it would not be possible
+ * to successfully return to the failing instruction. This is the
+ * cause of the second #PF captured here having the SGX bit set,
+ * it is from hardware preventing the page from being used.
+ */
+ put_addr_op.value = MAGIC;
+ put_addr_op.addr = (unsigned long)addr;
+ put_addr_op.header.type = ENCL_OP_PUT_TO_ADDRESS;
+
+ EXPECT_EQ(ENCL_CALL(&put_addr_op, &self->run, true), 0);
+
+ EXPECT_EQ(self->run.function, ERESUME);
+ EXPECT_EQ(self->run.exception_vector, 14);
+ EXPECT_EQ(self->run.exception_addr, (unsigned long)addr);
+
+ if (self->run.exception_error_code == 0x6) {
+ munmap(addr, PAGE_SIZE);
+ SKIP(return, "Kernel does not support adding pages to initialized enclave");
+ }
+
+ EXPECT_EQ(self->run.exception_error_code, 0x8007);
+
+ self->run.exception_vector = 0;
+ self->run.exception_error_code = 0;
+ self->run.exception_addr = 0;
+
+ /* Handle AEX by running EACCEPT from new entry point. */
+ self->run.tcs = self->encl.encl_base + PAGE_SIZE;
+
+ eaccept_op.epc_addr = self->encl.encl_base + total_size;
+ eaccept_op.flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_REG | SGX_SECINFO_PENDING;
+ eaccept_op.ret = 0;
+ eaccept_op.header.type = ENCL_OP_EACCEPT;
+
+ EXPECT_EQ(ENCL_CALL(&eaccept_op, &self->run, true), 0);
+
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+ EXPECT_EQ(eaccept_op.ret, 0);
+
+ /* Can now return to main TCS to resume execution. */
+ self->run.tcs = self->encl.encl_base;
+
+ EXPECT_EQ(vdso_sgx_enter_enclave((unsigned long)&put_addr_op, 0, 0,
+ ERESUME, 0, 0,
+ &self->run),
+ 0);
+
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+
+ /*
+ * Read memory from newly added page that was just written to,
+ * confirming that data previously written (MAGIC) is present.
+ */
+ get_addr_op.value = 0;
+ get_addr_op.addr = (unsigned long)addr;
+ get_addr_op.header.type = ENCL_OP_GET_FROM_ADDRESS;
+
+ EXPECT_EQ(ENCL_CALL(&get_addr_op, &self->run, true), 0);
+
+ EXPECT_EQ(get_addr_op.value, MAGIC);
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+
+ munmap(addr, PAGE_SIZE);
+}
+
+/*
+ * Test for the addition of pages to an initialized enclave via a
+ * pre-emptive run of EACCEPT on page to be added.
+ */
+TEST_F(enclave, augment_via_eaccept)
+{
+ struct encl_op_get_from_addr get_addr_op;
+ struct encl_op_put_to_addr put_addr_op;
+ struct encl_op_eaccept eaccept_op;
+ size_t total_size = 0;
+ void *addr;
+ int i;
+
+ if (!sgx2_supported())
+ SKIP(return, "SGX2 not supported");
+
+ 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;
+
+ for (i = 0; i < self->encl.nr_segments; i++) {
+ struct encl_segment *seg = &self->encl.segment_tbl[i];
+
+ total_size += seg->size;
+ }
+
+ /*
+ * Actual enclave size is expected to be larger than the loaded
+ * test enclave since enclave size must be a power of 2 in bytes while
+ * test_encl does not consume it all.
+ */
+ EXPECT_LT(total_size + PAGE_SIZE, self->encl.encl_size);
+
+ /*
+ * mmap() a page at end of existing enclave to be used for dynamic
+ * EPC page.
+ */
+
+ addr = mmap((void *)self->encl.encl_base + total_size, PAGE_SIZE,
+ PROT_READ | PROT_WRITE | PROT_EXEC, MAP_SHARED | MAP_FIXED,
+ self->encl.fd, 0);
+ EXPECT_NE(addr, MAP_FAILED);
+
+ self->run.exception_vector = 0;
+ self->run.exception_error_code = 0;
+ self->run.exception_addr = 0;
+
+ /*
+ * Run EACCEPT on new page to trigger the #PF->EAUG->EACCEPT(again
+ * without a #PF). All should be transparent to userspace.
+ */
+ eaccept_op.epc_addr = self->encl.encl_base + total_size;
+ eaccept_op.flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_REG | SGX_SECINFO_PENDING;
+ eaccept_op.ret = 0;
+ eaccept_op.header.type = ENCL_OP_EACCEPT;
+
+ EXPECT_EQ(ENCL_CALL(&eaccept_op, &self->run, true), 0);
+
+ if (self->run.exception_vector == 14 &&
+ self->run.exception_error_code == 4 &&
+ self->run.exception_addr == self->encl.encl_base + total_size) {
+ munmap(addr, PAGE_SIZE);
+ SKIP(return, "Kernel does not support adding pages to initialized enclave");
+ }
+
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+ EXPECT_EQ(eaccept_op.ret, 0);
+
+ /*
+ * New page should be accessible from within enclave - attempt to
+ * write to it.
+ */
+ put_addr_op.value = MAGIC;
+ put_addr_op.addr = (unsigned long)addr;
+ put_addr_op.header.type = ENCL_OP_PUT_TO_ADDRESS;
+
+ EXPECT_EQ(ENCL_CALL(&put_addr_op, &self->run, true), 0);
+
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+
+ /*
+ * Read memory from newly added page that was just written to,
+ * confirming that data previously written (MAGIC) is present.
+ */
+ get_addr_op.value = 0;
+ get_addr_op.addr = (unsigned long)addr;
+ get_addr_op.header.type = ENCL_OP_GET_FROM_ADDRESS;
+
+ EXPECT_EQ(ENCL_CALL(&get_addr_op, &self->run, true), 0);
+
+ EXPECT_EQ(get_addr_op.value, MAGIC);
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+
+ munmap(addr, PAGE_SIZE);
+}
+
TEST_HARNESS_MAIN
--
2.25.1