linux-kernel - [PATCH] selftest/sgx: Use rip relative addressing for encl

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Message-Id: <20220322001742.34974-1-jarkko@kernel.org>
Date:   Tue, 22 Mar 2022 02:17:41 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     linux-sgx@...r.kernel.org
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        linux-kselftest@...r.kernel.org (open list:KERNEL SELFTEST FRAMEWORK),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] selftest/sgx: Use rip relative addressing for encl_stack

Simplify the test_encl_bootstrap.S flow by using rip-relative addressing.
Compiler does the right thing here, and this removes dependency on where
TCS entries need to be located in the binary, i.e. allows the binary layout
changed freely in the future.

Cc: Reinette Chatre <reinette.chatre@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
This has been in my mind for a while and since the kselftest is
seemingly growing, I thought it is better to get rid off such an
artificial limitation on the binary layout.
 tools/testing/selftests/sgx/test_encl_bootstrap.S | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S
index 82fb0dfcbd23..1c1b5c6c4ffe 100644
--- a/tools/testing/selftests/sgx/test_encl_bootstrap.S
+++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S
@@ -40,11 +40,7 @@
 	.text
 
 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
+	lea	(encl_stack)(%rip), %rax
 	xchg	%rsp, %rax
 	push	%rax
 
-- 
2.35.1