[PATCH 2/8] selftests/sgx: Produce static-pie executable for test enclave

[Jo Van Bulck]

The current combination of -static and -fPIC creates a static executable
with position-dependent addresses for global variables. Use -static-pie
and -fPIE to create a proper static position independent executable that
can be loaded at any address without a dynamic linker.

Link: https://lore.kernel.org/all/f9c24d89-ed72-7d9e-c650-050d722c6b04@xxxxxxxxxxxxxx/
Signed-off-by: Jo Van Bulck <jo.vanbulck@xxxxxxxxxxxxxx>
---
 tools/testing/selftests/sgx/Makefile              |  2 +-
 tools/testing/selftests/sgx/test_encl.lds         |  1 +
 tools/testing/selftests/sgx/test_encl_bootstrap.S | 12 ++++++------
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/sgx/Makefile b/tools/testing/selftests/sgx/Makefile
index 50aab6b57da3..1d6315a2e5f5 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-pie -nostdlib -nostartfiles -fPIE \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)
 
 TEST_CUSTOM_PROGS := $(OUTPUT)/test_sgx
diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
index a1ec64f7d91f..ca659db2a534 100644
--- a/tools/testing/selftests/sgx/test_encl.lds
+++ b/tools/testing/selftests/sgx/test_encl.lds
@@ -10,6 +10,7 @@ PHDRS
 SECTIONS
 {
 	. = 0;
+        __enclave_base = .;
 	.tcs : {
 		*(.tcs*)
 	} : tcs
diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S
index 03ae0f57e29d..c91743f14312 100644
--- a/tools/testing/selftests/sgx/test_encl_bootstrap.S
+++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S
@@ -42,9 +42,12 @@
 encl_entry:
 	# RBX contains the base address for TCS, which is the first address
 	# inside the enclave for TCS #1 and one page into the enclave for
-	# TCS #2. By adding the value of encl_stack to it, we get
-	# the absolute address for the stack.
-	lea	(encl_stack)(%rbx), %rax
+	# TCS #2. First make it relative by substracting __enclave_base and
+	# then add the address of encl_stack to get the address for the stack.
+	lea __enclave_base(%rip), %rax
+	sub %rax, %rbx
+	lea encl_stack(%rip), %rax
+	add %rbx, %rax
 	jmp encl_entry_core
 encl_dyn_entry:
 	# Entry point for dynamically created TCS page expected to follow
@@ -55,12 +58,9 @@ encl_entry_core:
 	push	%rax
 
 	push	%rcx # push the address after EENTER
-	push	%rbx # push the enclave base address
 
 	call	encl_body
 
-	pop	%rbx # pop the enclave base address
-
 	/* Clear volatile GPRs, except RAX (EEXIT function). */
 	xor     %rcx, %rcx
 	xor     %rdx, %rdx
-- 
2.34.1