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X-CSE-ConnectionGUID: KD/CZgHIQSaKq5UYl19K9w== X-CSE-MsgGUID: btl4UpChQ8ad/DC/bgwmqA== X-IronPort-AV: E=McAfee;i="6700,10204,11234"; a="40695411" X-IronPort-AV: E=Sophos;i="6.11,226,1725346800"; d="scan'208";a="40695411" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2024 09:51:58 -0700 X-CSE-ConnectionGUID: ILx0V+eORuWSVE0ZoH8Ggg== X-CSE-MsgGUID: blE4w4hCRXGtp82vFwdQTg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,226,1725346800"; d="scan'208";a="84897952" Received: from rfrazer-mobl3.amr.corp.intel.com (HELO [10.124.221.6]) ([10.124.221.6]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2024 09:51:56 -0700 Message-ID: <6b575236-7e4e-4128-9ab6-7ecec7b81428@intel.com> Date: Wed, 23 Oct 2024 09:51:55 -0700 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/5] selftests/mm: Use generic pkey register manipulation To: Kevin Brodsky , linux-arm-kernel@lists.infradead.org Cc: akpm@linux-foundation.org, anshuman.khandual@arm.com, aruna.ramakrishna@oracle.com, broonie@kernel.org, catalin.marinas@arm.com, dave.hansen@linux.intel.com, dave.martin@arm.com, jeffxu@chromium.org, joey.gouly@arm.com, pierre.langlois@arm.com, shuah@kernel.org, sroettger@google.com, will@kernel.org, linux-kselftest@vger.kernel.org, x86@kernel.org References: <20241023150511.3923558-1-kevin.brodsky@arm.com> <20241023150511.3923558-5-kevin.brodsky@arm.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/23/24 08:05, Kevin Brodsky wrote: ...> diff --git a/tools/testing/selftests/mm/pkey-x86.h b/tools/testing/selftests/mm/pkey-x86.h > index 5f28e26a2511..53ed9a336ffe 100644 > --- a/tools/testing/selftests/mm/pkey-x86.h > +++ b/tools/testing/selftests/mm/pkey-x86.h > @@ -34,6 +34,8 @@ > #define PAGE_SIZE 4096 > #define MB (1<<20) > > +#define PKEY_ALLOW_NONE 0x55555555 Hi Kevin, Looking at this in context, I think "PKEY_ALLOW_NONE" is not a great name. On one hand, we have: PKEY_DISABLE_ACCESS PKEY_DISABLE_WRITE which are values for *A* pkey. But PKEY_ALLOW_NONE is a whole register value and spans permissions for many keys. We don't want folks trying to do something like: pkey_alloc(flags, PKEY_ALLOW_NONE); If I were naming it in x86 code, I'd probably call it: PKRU_ALLOW_NONE or something. > static inline void __page_o_noops(void) > { > /* 8-bytes of instruction * 512 bytes = 1 page */ > diff --git a/tools/testing/selftests/mm/pkey_sighandler_tests.c b/tools/testing/selftests/mm/pkey_sighandler_tests.c > index a8088b645ad6..b5e1767ee5d9 100644 > --- a/tools/testing/selftests/mm/pkey_sighandler_tests.c > +++ b/tools/testing/selftests/mm/pkey_sighandler_tests.c > @@ -37,6 +37,8 @@ pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; > pthread_cond_t cond = PTHREAD_COND_INITIALIZER; > siginfo_t siginfo = {0}; > > +static u64 pkey_reg_no_access; Ideally, this would be a real const or a #define because it really is static. Right? Or is there something dynamic about the ARM implementation's value? ... > * Setup alternate signal stack, which should be pkey_mprotect()ed by > @@ -142,7 +145,8 @@ static void *thread_segv_maperr_ptr(void *ptr) > syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0); > > /* Disable MPK 0. Only MPK 1 is enabled. */ > - __write_pkey_reg(0x55555551); > + pkey_reg = set_pkey_bits(pkey_reg_no_access, 1, 0); > + __write_pkey_reg(pkey_reg); The existing magic numbers are not great, but could we do: #define PKEY_ALLOW_ALL 0x0 So that this can be written like this: pkey_reg = PKRU_ALLOW_NONE; pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL); That would get rid of the magic '0'. > /* Segfault */ > *bad = 1; > @@ -240,6 +244,7 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void) > int pkey; > int parent_pid = 0; > int child_pid = 0; > + u64 pkey_reg; > > sa.sa_flags = SA_SIGINFO | SA_ONSTACK; > > @@ -257,7 +262,9 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void) > assert(stack != MAP_FAILED); > > /* Allow access to MPK 0 and MPK 1 */ > - __write_pkey_reg(0x55555550); > + pkey_reg = set_pkey_bits(pkey_reg_no_access, 0, 0); > + pkey_reg = set_pkey_bits(pkey_reg, 1, 0); > + __write_pkey_reg(pkey_reg); ... and using the pattern from above, this is quite a bit more readable: pkey_reg = PKRU_ALLOW_NONE; pkey_reg = set_pkey_bits(pkey_reg, 0, PKEY_ALLOW_ALL); pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL); ... > + /* Only allow X for MPK 0 and nothing for other keys */ > + pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0, > + PKEY_DISABLE_ACCESS); If the comment says "only allow X", then I'd expect the code to say: pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0, PKEY_X); ... or something similar.