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

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Message-Id: <20230724165832.15797-5-jo.vanbulck@cs.kuleuven.be>
Date:   Mon, 24 Jul 2023 18:58:31 +0200
From:   Jo Van Bulck <jo.vanbulck@...kuleuven.be>
To:     jarkko@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com,
        Jo Van Bulck <jo.vanbulck@...kuleuven.be>
Subject: [PATCH 4/5] selftests/sgx: Ensure expected enclave data buffer size and placement.

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@...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