[PATCH v7 11/13] selftests/sgx: Ensure expected location of test enclave buffer

[Jo Van Bulck]

The external tests manipulating page permissions expect encl_buffer to be
placed at the start of the test enclave's .data section. As this is not
guaranteed per the C standard, explicitly place encl_buffer in a separate
section that is explicitly placed at the start of the .data segment in the
linker script to avoid the compiler placing it somewhere else in .data.

Signed-off-by: Jo Van Bulck <jo.vanbu...@cs.kuleuven.be>
Reviewed-by: Jarkko Sakkinen <jar...@kernel.org>
Acked-by: Kai Huang <kai.hu...@intel.com>
---
 tools/testing/selftests/sgx/defines.h     | 1 +
 tools/testing/selftests/sgx/test_encl.c   | 8 ++++----
 tools/testing/selftests/sgx/test_encl.lds | 1 +
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/sgx/defines.h 
b/tools/testing/selftests/sgx/defines.h
index b8f482667ce1..402f8787a71c 100644
--- a/tools/testing/selftests/sgx/defines.h
+++ b/tools/testing/selftests/sgx/defines.h
@@ -14,6 +14,7 @@
 #define __aligned(x) __attribute__((__aligned__(x)))
 #define __packed __attribute__((packed))
 #define __used __attribute__((used))
+#define __section(x)__attribute__((__section__(x)))
 
 #include "../../../../arch/x86/include/asm/sgx.h"
 #include "../../../../arch/x86/include/asm/enclu.h"
diff --git a/tools/testing/selftests/sgx/test_encl.c 
b/tools/testing/selftests/sgx/test_encl.c
index 7465f121fb74..2c4d709cce2d 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -6,11 +6,11 @@
 
 /*
  * Data buffer spanning two pages that will be placed first in the .data
- * segment. Even if not used internally the second page is needed by external
- * test manipulating page permissions, so mark encl_buffer as "used" to make
- * sure it is entirely preserved by the compiler.
+ * segment via the linker script. Even if not used internally the second page
+ * is needed by external test manipulating page permissions, so mark
+ * encl_buffer as "used" to make sure it is entirely preserved by the compiler.
  */
-static uint8_t __used encl_buffer[8192] = { 1 };
+static uint8_t __used __section(".data.encl_buffer") encl_buffer[8192] = { 1 };
 
 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 6ffdfc9fb4cf..333a3e78fdc9 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
 
-- 
2.25.1