linux-kernel - Re: [PATCH v3 7/9] selftests/sgx: Ensure expected location of test enclave buffer

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Message-ID: <b9e818ceedbe053b3d42b0e1853763ad0d47df50.camel@intel.com>
Date:   Mon, 21 Aug 2023 11:10:20 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Van Bulck, Jo" <jo.vanbulck@...kuleuven.be>
CC:     "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 7/9] selftests/sgx: Ensure expected location of test
 enclave buffer

On Sat, 2023-08-19 at 11:43 +0200, Jo Van Bulck wrote:
> The external tests manipulating page permissions expect encl_buffer to be
> placed at the start of the test enclave's .data section. As this is not
> guaranteed per the C standard, explicitly place encl_buffer in a separate
> section that is explicitly placed at the start of the .data segment in the
> linker script to avoid the compiler placing it somewhere else in .data.
> 
> Signed-off-by: Jo Van Bulck <jo.vanbulck@...kuleuven.be>
> ---
>  tools/testing/selftests/sgx/defines.h     | 1 +
>  tools/testing/selftests/sgx/test_encl.c   | 8 ++++----
>  tools/testing/selftests/sgx/test_encl.lds | 1 +
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/sgx/defines.h b/tools/testing/selftests/sgx/defines.h
> index b8f482667..402f8787a 100644
> --- a/tools/testing/selftests/sgx/defines.h
> +++ b/tools/testing/selftests/sgx/defines.h
> @@ -14,6 +14,7 @@
>  #define __aligned(x) __attribute__((__aligned__(x)))
>  #define __packed __attribute__((packed))
>  #define __used __attribute__((used))
> +#define __section(x)__attribute__((__section__(x)))
>  
>  #include "../../../../arch/x86/include/asm/sgx.h"
>  #include "../../../../arch/x86/include/asm/enclu.h"
> diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
> index c7bcbc85b..151600353 100644
> --- a/tools/testing/selftests/sgx/test_encl.c
> +++ b/tools/testing/selftests/sgx/test_encl.c
> @@ -6,11 +6,11 @@
>  
>  /*
>   * Data buffer spanning two pages that will be placed first in the .data
> - * segment. Even if not used internally the second page is needed by external
> - * test manipulating page permissions, so mark encl_buffer as "used" to make
> - * sure it is entirely preserved by the compiler.
> + * segment via the linker script. Even if not used internally the second page
> + * is needed by external test manipulating page permissions, so mark
> + * encl_buffer as "used" to make sure it is entirely preserved by the compiler.
>   */
> -static uint8_t __used encl_buffer[8192] = { 1 };
> +static uint8_t __used __section(".data.encl_buffer") encl_buffer[8192] = { 1 };
>  
>  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 13144b045..ffe851a1c 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
>  

Acked-by: Kai Huang <kai.huang@...el.com>