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Subject[PATCH 11/25] selftests/sgx: Add test for EPCM permission changes
Date
EPCM permission changes could be made from within (to extend
permissions) or out (to restrict permissions) the enclave. OS
support is needed when permissions are restricted to be able to
call the privileged ENCLS[EMODPR] instruction and ensure PTEs
allowing the restricted permissions are flushed. EPCM permissions
can be extended via ENCLU[EMODPE] from within the enclave.

Add a test that exercises a few of the enclave page permission flows:
1) Test starts with a RW (from enclave and OS perspective) enclave page
that is mapped via a RW VMA.
2) The SGX_IOC_PAGE_MODP ioctl is used to restrict the enclave (EPCM)
page permissions to read-only (OS removes page table entry in the
process).
3) Run ENCLU[EACCEPT] from within the enclave to accept the new page
permissions.
4) Attempt to write to the enclave page from within the enclave - this
should fail with a page fault on the page table entry since the page
table entry accurately reflects the EPCM permissions.
5) Restore EPCM permissions to RW by running ENCLU[EMODPE] from within
the enclave.
6) Attempt to write to the enclave page from within the enclave - this
should fail again with a page fault because even though the EPCM
permissions are RW the page table entries do not yet reflect that.
7) The SGX_IOC_PAGE_MODP ioctl is used to inform OS of new page
permissions and page table entries will accurately reflect RW EPCM
permissions.
8) Writing to enclave page from within enclave succeeds.
9) Ensure EPCM.PR is clear by running ENCLU[EACCEPT].

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
tools/testing/selftests/sgx/defines.h | 15 ++
tools/testing/selftests/sgx/main.c | 264 ++++++++++++++++++++++++
tools/testing/selftests/sgx/test_encl.c | 38 ++++
3 files changed, 317 insertions(+)

diff --git a/tools/testing/selftests/sgx/defines.h b/tools/testing/selftests/sgx/defines.h
index 02d775789ea7..b638eb98c80c 100644
--- a/tools/testing/selftests/sgx/defines.h
+++ b/tools/testing/selftests/sgx/defines.h
@@ -24,6 +24,8 @@ enum encl_op_type {
ENCL_OP_PUT_TO_ADDRESS,
ENCL_OP_GET_FROM_ADDRESS,
ENCL_OP_NOP,
+ ENCL_OP_EACCEPT,
+ ENCL_OP_EMODPE,
ENCL_OP_MAX,
};

@@ -53,4 +55,17 @@ struct encl_op_get_from_addr {
uint64_t addr;
};

+struct encl_op_eaccept {
+ struct encl_op_header header;
+ uint64_t epc_addr;
+ uint64_t flags;
+ uint64_t ret;
+};
+
+struct encl_op_emodpe {
+ struct encl_op_header header;
+ uint64_t epc_addr;
+ uint64_t flags;
+};
+
#endif /* DEFINES_H */
diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index 7e912db4c6c5..dbd071ba03fe 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -24,6 +24,18 @@ static const uint64_t MAGIC = 0x1122334455667788ULL;
static const uint64_t MAGIC2 = 0x8877665544332211ULL;
vdso_sgx_enter_enclave_t vdso_sgx_enter_enclave;

+/*
+ * Security Information (SECINFO) data structure needed by a few SGX
+ * instructions (eg. ENCLU[EACCEPT] and ENCLU[EMODPE]) holds meta-data
+ * about an enclave page. &enum sgx_secinfo_page_state specifies the
+ * secinfo flags used for page state.
+ */
+enum sgx_secinfo_page_state {
+ SGX_SECINFO_PENDING = (1 << 3),
+ SGX_SECINFO_MODIFIED = (1 << 4),
+ SGX_SECINFO_PR = (1 << 5),
+};
+
struct vdso_symtab {
Elf64_Sym *elf_symtab;
const char *elf_symstrtab;
@@ -555,4 +567,256 @@ TEST_F(enclave, pte_permissions)
EXPECT_EQ(self->run.exception_addr, 0);
}

+/*
+ * Enclave page permission test.
+ *
+ * Modify and restore enclave page's EPCM (enclave) permissions from
+ * outside enclave (ENCLS[EMODPR] via OS) as well as from within enclave (via
+ * ENCLU[EMODPE]). Kernel should ensure PTE permissions are the same as
+ * the EPCM permissions so check for page fault if VMA allows access but
+ * EPCM and PTE does not.
+ */
+TEST_F(enclave, epcm_permissions)
+{
+ struct encl_op_get_from_addr get_addr_op;
+ struct encl_op_put_to_addr put_addr_op;
+ struct encl_op_eaccept eaccept_op;
+ struct encl_op_emodpe emodpe_op;
+ unsigned long data_start;
+ struct sgx_page_modp ioc;
+ 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;
+
+ /*
+ * Ensure kernel supports needed ioctl and system supports needed
+ * commands.
+ */
+ memset(&ioc, 0, sizeof(ioc));
+
+ ret = ioctl(self->encl.fd, SGX_IOC_PAGE_MODP, &ioc);
+
+ if (ret == -1) {
+ if (errno == ENOTTY)
+ SKIP(return, "Kernel does not support test SGX_IOC_PAGE_MODP ioctl");
+ else if (errno == ENODEV)
+ SKIP(return, "System does not support SGX2");
+ }
+
+ /*
+ * Invalid parameters were provided during sanity check,
+ * expect command to fail.
+ */
+ EXPECT_EQ(ret, -1);
+
+ /*
+ * Page that will have its permissions changed is the second data
+ * page in the .data segment. This forms part of the local encl_buffer
+ * within the enclave.
+ *
+ * At start of test @data_start should have EPCM as well as PTE
+ * permissions of RW.
+ */
+
+ data_start = self->encl.encl_base +
+ encl_get_data_offset(&self->encl) + PAGE_SIZE;
+
+ /*
+ * Sanity check that page at @data_start is writable before making
+ * any changes to page permissions.
+ *
+ * Start by writing MAGIC to test page.
+ */
+ put_addr_op.value = MAGIC;
+ put_addr_op.addr = data_start;
+ 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 that was just written to, confirming that
+ * page is writable.
+ */
+ get_addr_op.value = 0;
+ get_addr_op.addr = data_start;
+ 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);
+
+ /*
+ * Change EPCM permissions to read-only, PTE entry flushed by OS in
+ * the process.
+ */
+ memset(&ioc, 0, sizeof(ioc));
+
+ ioc.offset = encl_get_data_offset(&self->encl) + PAGE_SIZE;
+ ioc.length = PAGE_SIZE;
+ ioc.prot = PROT_READ;
+
+ ret = ioctl(self->encl.fd, SGX_IOC_PAGE_MODP, &ioc);
+ errno_save = ret == -1 ? errno : 0;
+
+ EXPECT_EQ(ret, 0);
+ EXPECT_EQ(errno_save, 0);
+ EXPECT_EQ(ioc.result, 0);
+ EXPECT_EQ(ioc.count, 4096);
+
+ /*
+ * EPCM permissions changed from OS, need to EACCEPT from enclave.
+ */
+ eaccept_op.epc_addr = data_start;
+ eaccept_op.flags = PROT_READ | SGX_SECINFO_REG | SGX_SECINFO_PR;
+ 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);
+
+ /*
+ * EPCM permissions of page is now read-only, expect #PF
+ * on PTE (not EPCM) when attempting to write to page from
+ * within enclave.
+ */
+ put_addr_op.value = MAGIC2;
+
+ 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_error_code, 0x7);
+ EXPECT_EQ(self->run.exception_addr, data_start);
+
+ self->run.exception_vector = 0;
+ self->run.exception_error_code = 0;
+ self->run.exception_addr = 0;
+
+ /*
+ * Received AEX but cannot return to enclave at same entrypoint,
+ * need different TCS from where EPCM permission can be made writable
+ * again.
+ */
+ self->run.tcs = self->encl.encl_base + PAGE_SIZE;
+
+ /*
+ * Enter enclave at new TCS to change EPCM permissions to be
+ * writable again and thus fix the page fault that triggered the
+ * AEX.
+ */
+
+ emodpe_op.epc_addr = data_start;
+ emodpe_op.flags = PROT_READ | PROT_WRITE;
+ emodpe_op.header.type = ENCL_OP_EMODPE;
+
+ EXPECT_EQ(ENCL_CALL(&emodpe_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);
+
+ /*
+ * Attempt to return to main TCS to resume execution at faulting
+ * instruction, but PTE should still prevent writing to the page.
+ */
+ 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_EQ(self->run.function, ERESUME);
+ EXPECT_EQ(self->run.exception_vector, 14);
+ EXPECT_EQ(self->run.exception_error_code, 0x7);
+ EXPECT_EQ(self->run.exception_addr, data_start);
+
+ self->run.exception_vector = 0;
+ self->run.exception_error_code = 0;
+ self->run.exception_addr = 0;
+ /*
+ * Inform OS about new permissions to have PTEs match EPCM.
+ */
+ memset(&ioc, 0, sizeof(ioc));
+
+ ioc.offset = encl_get_data_offset(&self->encl) + PAGE_SIZE;
+ ioc.length = PAGE_SIZE;
+ ioc.prot = PROT_READ | PROT_WRITE;
+
+ ret = ioctl(self->encl.fd, SGX_IOC_PAGE_MODP, &ioc);
+ errno_save = ret == -1 ? errno : 0;
+
+ EXPECT_EQ(ret, 0);
+ EXPECT_EQ(errno_save, 0);
+ EXPECT_EQ(ioc.result, 0);
+ EXPECT_EQ(ioc.count, 4096);
+
+ /*
+ * Wrong page permissions that caused original fault has
+ * now been fixed via EPCM permissions as well as PTE.
+ * Resume execution in main TCS to re-attempt the memory access.
+ */
+ 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);
+
+ get_addr_op.value = 0;
+
+ EXPECT_EQ(ENCL_CALL(&get_addr_op, &self->run, true), 0);
+
+ EXPECT_EQ(get_addr_op.value, MAGIC2);
+ EXPECT_EEXIT(&self->run);
+ EXPECT_EQ(self->run.user_data, 0);
+ EXPECT_EQ(self->run.exception_vector, 0);
+ EXPECT_EQ(self->run.exception_error_code, 0);
+ EXPECT_EQ(self->run.exception_addr, 0);
+
+ /*
+ * The SGX_IOC_PAGE_MODP runs ENCLS[EMODPR] that sets EPCM.PR even
+ * if permissions are not actually restricted. The previous memory
+ * access succeeding shows that the PR flag does not prevent
+ * access. Even so, include an ENCLU[EACCEPT] as reference
+ * implementation to ensure EPCM does not have a dangling PR bit set.
+ */
+
+ eaccept_op.epc_addr = data_start;
+ eaccept_op.flags = PROT_READ | PROT_WRITE | SGX_SECINFO_REG | SGX_SECINFO_PR;
+ 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);
+}
+
TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
index 4fca01cfd898..5b6c65331527 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -11,6 +11,42 @@
*/
static uint8_t encl_buffer[8192] = { 1 };

+enum sgx_enclu_function {
+ EACCEPT = 0x5,
+ EMODPE = 0x6,
+};
+
+static void do_encl_emodpe(void *_op)
+{
+ struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
+ struct encl_op_emodpe *op = _op;
+
+ secinfo.flags = op->flags;
+
+ asm volatile(".byte 0x0f, 0x01, 0xd7"
+ :
+ : "a" (EMODPE),
+ "b" (&secinfo),
+ "c" (op->epc_addr));
+}
+
+static void do_encl_eaccept(void *_op)
+{
+ struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
+ struct encl_op_eaccept *op = _op;
+ int rax;
+
+ secinfo.flags = op->flags;
+
+ asm volatile(".byte 0x0f, 0x01, 0xd7"
+ : "=a" (rax)
+ : "a" (EACCEPT),
+ "b" (&secinfo),
+ "c" (op->epc_addr));
+
+ op->ret = rax;
+}
+
static void *memcpy(void *dest, const void *src, size_t n)
{
size_t i;
@@ -62,6 +98,8 @@ void encl_body(void *rdi, void *rsi)
do_encl_op_put_to_addr,
do_encl_op_get_from_addr,
do_encl_op_nop,
+ do_encl_eaccept,
+ do_encl_emodpe,
};

struct encl_op_header *op = (struct encl_op_header *)rdi;
--
2.25.1
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