[PATCH 3/8] selftests/sgx: Handle relocations in test enclave

[Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>]

Static-pie binaries normally include a startup routine to perform any ELF
relocations from .rela.dyn. Since the enclave loading process is different
and glibc is not included, do the necessary relocation for encl_op_array
entries manually at runtime relative to the enclave base to ensure correct
function pointers.

Signed-off-by: Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>
---
 tools/testing/selftests/sgx/test_encl.c   | 35 +++++++++++++++--------
 tools/testing/selftests/sgx/test_encl.lds |  3 ++
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
index c0d6397295e3..c71dfbadd2d9 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -119,21 +119,32 @@ static void do_encl_op_nop(void *_op)
 
 }
 
+/*
+ * Symbol placed at the start of the enclave image by the linker script.
+ * Declare this extern symbol with visibility "hidden" to ensure the
+ * compiler does not access it through the GOT.
+ */
+extern uint8_t __attribute__((visibility("hidden"))) __enclave_base;
+
+void (*encl_op_array[ENCL_OP_MAX])(void *) = {
+	do_encl_op_put_to_buf,
+	do_encl_op_get_from_buf,
+	do_encl_op_put_to_addr,
+	do_encl_op_get_from_addr,
+	do_encl_op_nop,
+	do_encl_eaccept,
+	do_encl_emodpe,
+	do_encl_init_tcs_page,
+};
+
 void encl_body(void *rdi,  void *rsi)
 {
-	const void (*encl_op_array[ENCL_OP_MAX])(void *) = {
-		do_encl_op_put_to_buf,
-		do_encl_op_get_from_buf,
-		do_encl_op_put_to_addr,
-		do_encl_op_get_from_addr,
-		do_encl_op_nop,
-		do_encl_eaccept,
-		do_encl_emodpe,
-		do_encl_init_tcs_page,
-	};
-
 	struct encl_op_header *op = (struct encl_op_header *)rdi;
 
+	/*
+	 * Manually rebase the loaded function pointer as enclaves cannot
+	 * rely on startup routines to perform static pie relocations.
+	 */
 	if (op->type < ENCL_OP_MAX)
-		(*encl_op_array[op->type])(op);
+		(*(((uint64_t) &__enclave_base) + encl_op_array[op->type]))(op);
 }
diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
index ca659db2a534..73d9c8bbe7de 100644
--- a/tools/testing/selftests/sgx/test_encl.lds
+++ b/tools/testing/selftests/sgx/test_encl.lds
@@ -32,6 +32,9 @@ SECTIONS
 		*(.note*)
 		*(.debug*)
 		*(.eh_frame*)
+		/* Dynamic symbol table not supported in enclaves */
+		*(.dyn*)
+		*(.gnu.hash)
 	}
 }
 
-- 
2.34.1