linux-kernel - Re: [PATCH v3 6/9] selftests/sgx: Ensure test enclave buffer is entirely preserved

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Message-ID: <555e9e6dff49a460d51de4c25ce8016343cd691a.camel@intel.com>
Date:   Mon, 21 Aug 2023 11:10:12 +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 6/9] selftests/sgx: Ensure test enclave buffer is
 entirely preserved

On Sat, 2023-08-19 at 11:43 +0200, Jo Van Bulck wrote:
> Attach the "used" attribute to instruct the compiler to preserve the static
> encl_buffer, even if it appears it is not entirely referenced in the enclave
> code, as expected by the external tests manipulating page permissions.
> 
> Link: https://lore.kernel.org/all/a2732938-f3db-a0af-3d68-a18060f66e79@cs.kuleuven.be/
> Signed-off-by: Jo Van Bulck <jo.vanbulck@...kuleuven.be>
> ---
>  tools/testing/selftests/sgx/defines.h   | 1 +
>  tools/testing/selftests/sgx/test_encl.c | 9 +++++----
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/sgx/defines.h b/tools/testing/selftests/sgx/defines.h
> index d8587c971..b8f482667 100644
> --- a/tools/testing/selftests/sgx/defines.h
> +++ b/tools/testing/selftests/sgx/defines.h
> @@ -13,6 +13,7 @@
>  
>  #define __aligned(x) __attribute__((__aligned__(x)))
>  #define __packed __attribute__((packed))
> +#define __used __attribute__((used))
>  
>  #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 b09550cb3..c7bcbc85b 100644
> --- a/tools/testing/selftests/sgx/test_encl.c
> +++ b/tools/testing/selftests/sgx/test_encl.c
> @@ -5,11 +5,12 @@
>  #include "defines.h"
>  
>  /*
> - * Data buffer spanning two pages that will be placed first in .data
> - * segment. Even if not used internally the second page is needed by
> - * external test manipulating page permissions.
> + * 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.
>   */
> -static uint8_t encl_buffer[8192] = { 1 };
> +static uint8_t __used encl_buffer[8192] = { 1 };
>  
>  enum sgx_enclu_function {
>  	EACCEPT = 0x5,

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