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

[Jarkko Sakkinen]

On Sat Aug 19, 2023 at 12:43 PM EEST, 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@xxxxxxxxxxxxxx>
> ---
>  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
>  
> -- 
> 2.25.1

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko