linux-kernel - [tip: x86/sgx] selftests/sgx: Produce static-pie executable for test enclave

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Date:   Fri, 08 Dec 2023 18:12:59 -0000
From:   "tip-bot2 for Jo Van Bulck" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jo Van Bulck <jo.vanbulck@...kuleuven.be>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Kai Huang <kai.huang@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/sgx] selftests/sgx: Produce static-pie executable for test enclave

The following commit has been merged into the x86/sgx branch of tip:

Commit-ID:     f7884e732841450de36c2b1ed49b91e8e854a7d1
Gitweb:        https://git.kernel.org/tip/f7884e732841450de36c2b1ed49b91e8e854a7d1
Author:        Jo Van Bulck <jo.vanbulck@...kuleuven.be>
AuthorDate:    Thu, 05 Oct 2023 17:38:48 +02:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Fri, 08 Dec 2023 10:05:27 -08:00

selftests/sgx: Produce static-pie executable for test enclave

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.

When building the original "lea (encl_stack)(%rbx), %rax" assembly code
with -static-pie -fPIE, the linker complains about a relocation it cannot
resolve:

/usr/local/bin/ld: /tmp/cchIWyfG.o: relocation R_X86_64_32S against
`.data' can not be used when making a PIE object; recompile with -fPIE
collect2: error: ld returned 1 exit status

Thus, since only RIP-relative addressing is legit for local symbols, use
"encl_stack(%rip)" and declare an explicit "__encl_base" symbol at the
start of the linker script to be able to calculate the stack address
relative to the current TCS in the enclave assembly entry code.

Signed-off-by: Jo Van Bulck <jo.vanbulck@...kuleuven.be>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
Acked-by: Kai Huang <kai.huang@...el.com>
Link: https://lore.kernel.org/all/f9c24d89-ed72-7d9e-c650-050d722c6b04@cs.kuleuven.be/
Link: https://lore.kernel.org/all/20231005153854.25566-8-jo.vanbulck%40cs.kuleuven.be
---
 tools/testing/selftests/sgx/Makefile              |  2 +-
 tools/testing/selftests/sgx/test_encl.lds         |  1 +
 tools/testing/selftests/sgx/test_encl_bootstrap.S |  9 ++++++---
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/sgx/Makefile b/tools/testing/selftests/sgx/Makefile
index 7eb890b..8d2ba6a 100644
--- a/tools/testing/selftests/sgx/Makefile
+++ b/tools/testing/selftests/sgx/Makefile
@@ -14,7 +14,7 @@ endif
 INCLUDES := -I$(top_srcdir)/tools/include
 HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC
 HOST_LDFLAGS := -z noexecstack -lcrypto
-ENCL_CFLAGS += -Wall -Werror -static -nostdlib -ffreestanding -fPIC \
+ENCL_CFLAGS += -Wall -Werror -static-pie -nostdlib -ffreestanding -fPIE \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)
 ENCL_LDFLAGS := -Wl,-T,test_encl.lds,--build-id=none
 
diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
index a1ec64f..62d3716 100644
--- a/tools/testing/selftests/sgx/test_encl.lds
+++ b/tools/testing/selftests/sgx/test_encl.lds
@@ -10,6 +10,7 @@ PHDRS
 SECTIONS
 {
 	. = 0;
+        __encl_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 e0ce993..28fe5d2 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 __encl_base and
+	# then add the address of encl_stack to get the address for the stack.
+	lea __encl_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