[PATCH 4/5] selftests/sgx: Ensure expected enclave data buffer size and placement.

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

Do not declare the enclave data buffer static to ensure it is not optimized
away by the compiler, even when not used entirely by the test enclave code.
Use -fPIE to make the compiler access the non-static buffer with
RIP-relative addressing. Place the enclave data buffer in a separate
section that is explicitly placed at the start of the .data segment in the
linker script, as expected by the external tests manipulating page
permissions.

Signed-off-by: Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>
---
 tools/testing/selftests/sgx/Makefile      | 2 +-
 tools/testing/selftests/sgx/test_encl.c   | 5 +++--
 tools/testing/selftests/sgx/test_encl.lds | 1 +
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/sgx/Makefile b/tools/testing/selftests/sgx/Makefile
index 50aab6b57da3..c5483445ba28 100644
--- a/tools/testing/selftests/sgx/Makefile
+++ b/tools/testing/selftests/sgx/Makefile
@@ -13,7 +13,7 @@ endif
 
 INCLUDES := -I$(top_srcdir)/tools/include
 HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC -z noexecstack
-ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIC \
+ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIE \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)
 
 TEST_CUSTOM_PROGS := $(OUTPUT)/test_sgx
diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
index aba301abefb8..5c274e517d13 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -7,9 +7,10 @@
 /*
  * Data buffer spanning two pages that will be placed first in .data
  * segment. Even if not used internally the second page is needed by
- * external test manipulating page permissions.
+ * external test manipulating page permissions. Do not declare this
+ * buffer as static, so the compiler cannot optimize it out.
  */
-static uint8_t encl_buffer[8192] = { 1 };
+uint8_t __attribute__((section(".data.encl_buffer"))) encl_buffer[8192];
 
 enum sgx_enclu_function {
 	EACCEPT = 0x5,
diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
index ca659db2a534..79b1e41d8d24 100644
--- a/tools/testing/selftests/sgx/test_encl.lds
+++ b/tools/testing/selftests/sgx/test_encl.lds
@@ -24,6 +24,7 @@ SECTIONS
 	} : text
 
 	.data : {
+		*(.data.encl_buffer)
 		*(.data*)
 	} : data
 
-- 
2.34.1