[PATCH v4 03/13] 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>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 tools/testing/selftests/sgx/test_encl.c | 48 +++++++++++++++++--------
 1 file changed, 33 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
index c0d6397295e3..706c1f7260ff 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -119,21 +119,39 @@ 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 const uint8_t __attribute__((visibility("hidden"))) __encl_base;
+
+typedef void (*encl_op_t)(void *);
+static const encl_op_t encl_op_array[ENCL_OP_MAX] = {
+	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;
-
-	if (op->type < ENCL_OP_MAX)
-		(*encl_op_array[op->type])(op);
+	struct encl_op_header *header = (struct encl_op_header *)rdi;
+	encl_op_t op;
+
+	if (header->type >= ENCL_OP_MAX)
+		return;
+
+	/*
+	 * The enclave base address needs to be added, as this call site
+	 * *cannot be* made rip-relative by the compiler, or fixed up by
+	 * any other possible means.
+	 */
+	op = ((uint64_t)&__encl_base) + encl_op_array[header->type];
+
+	(*op)(header);
 }
-- 
2.25.1