[PATCH 2/4] selftests/sgx: Store base address and size in test enclave

[Jo Van Bulck]

Make the test enclave aware of its protected virtual address range to allow
untrusted pointer argument range checks.

Add a linker symbol for __enclave_base at the start of the enclave binary.
Similar to real-world enclave runtimes, rely on the untrusted loader to
fill in __enclave_size (measured as part of MRENCLAVE), as the final size
of the enclave image is determined during loading.

Signed-off-by: Jo Van Bulck <jo.vanbulck@xxxxxxxxxxxxxx>
---
 tools/testing/selftests/sgx/load.c            |  3 +-
 tools/testing/selftests/sgx/main.c            | 32 +++++++++++++++++++
 tools/testing/selftests/sgx/test_encl.lds     |  1 +
 .../selftests/sgx/test_encl_bootstrap.S       | 17 ++++++++++
 4 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/sgx/load.c b/tools/testing/selftests/sgx/load.c
index 94bdeac1c..968a656a3 100644
--- a/tools/testing/selftests/sgx/load.c
+++ b/tools/testing/selftests/sgx/load.c
@@ -60,7 +60,8 @@ static bool encl_map_bin(const char *path, struct encl *encl)
 		goto err;
 	}
 
-	bin = mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	/* NOTE: map read|write to allow __enclave_size to be filled in */
+	bin = mmap(NULL, sb.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 	if (bin == MAP_FAILED) {
 		perror("enclave executable mmap()");
 		goto err;
diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index 9a671dbc6..b1a7988c1 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -178,6 +178,7 @@ static bool setup_test_encl(unsigned long heap_size, struct encl *encl,
 	Elf64_Sym *sgx_enter_enclave_sym = NULL;
 	struct vdso_symtab symtab;
 	struct encl_segment *seg;
+	uint64_t encl_size_pt;
 	char maps_line[256];
 	FILE *maps_file;
 	unsigned int i;
@@ -189,6 +190,16 @@ static bool setup_test_encl(unsigned long heap_size, struct encl *encl,
 		return false;
 	}
 
+	/*
+	 * Fill in the expected symbol location with the final size of the
+	 * constructed enclave image.
+	 */
+	encl_size_pt = encl_get_entry(encl, "__enclave_size");
+	if (encl_size_pt) {
+		encl_size_pt += (uint64_t) encl->src;
+		*((uint64_t *) encl_size_pt) = encl->encl_size;
+	}
+
 	if (!encl_measure(encl))
 		goto err;
 
@@ -307,6 +318,27 @@ TEST_F(enclave, unclobbered_vdso)
 	EXPECT_EQ(self->run.user_data, 0);
 }
 
+/*
+ * Sanity check that the loader correctly initializes __enclave_size in the
+ * measured enclave image.
+ */
+TEST_F(enclave, init_size)
+{
+	struct encl_op_get_from_addr get_addr_op;
+
+	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;
+
+	get_addr_op.value = 0;
+	get_addr_op.addr = self->encl.encl_base + encl_get_entry(&self->encl, "__enclave_size");
+	get_addr_op.header.type = ENCL_OP_GET_FROM_ADDRESS;
+	EXPECT_EQ(ENCL_CALL(&get_addr_op, &self->run, false), 0);
+	EXPECT_EEXIT(&self->run);
+	EXPECT_EQ(get_addr_op.value, self->encl.encl_size);
+}
+
 /*
  * Sanity check that the test enclave properly sanitizes untrusted
  * CPU configuration registers.
diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
index a1ec64f7d..ca659db2a 100644
--- a/tools/testing/selftests/sgx/test_encl.lds
+++ b/tools/testing/selftests/sgx/test_encl.lds
@@ -10,6 +10,7 @@ PHDRS
 SECTIONS
 {
 	. = 0;
+        __enclave_base = .;
 	.tcs : {
 		*(.tcs*)
 	} : tcs
diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S
index 3b69fea61..444a075c0 100644
--- a/tools/testing/selftests/sgx/test_encl_bootstrap.S
+++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S
@@ -98,6 +98,23 @@ encl_entry_core:
 	mov	$4, %rax
 	enclu
 
+	.global get_enclave_base
+get_enclave_base:
+	lea __enclave_base(%rip), %rax
+	ret
+
+	.global get_enclave_size
+get_enclave_size:
+	mov __enclave_size(%rip), %rax
+	ret
+
+	# The following 8 bytes (measured as part of MRENCLAVE) will be
+	# filled in by the untrusted loader with the total size of the
+	# loaded enclave.
+	.global __enclave_size
+__enclave_size:
+	.quad 0x0
+
 	.section ".data", "aw"
 
 encl_ssa_tcs1:
-- 
2.34.1