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

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Message-Id: <CUP3YJ000CVB.1DGFMB8XHFOSW@suppilovahvero>
Date:   Thu, 10 Aug 2023 22:22:47 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Jo Van Bulck" <jo.vanbulck@...kuleuven.be>, <kai.huang@...el.com>,
        <linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc:     <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 2/8] selftests/sgx: Produce static-pie executable for
 test enclave

On Tue Aug 8, 2023 at 10:31 PM EEST, Jo Van Bulck wrote:
> 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@cs.kuleuven.be/
> Signed-off-by: Jo Van Bulck <jo.vanbulck@...kuleuven.be>
> ---
>  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

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko