From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C385C130ADA; Tue, 11 Jun 2024 07:50:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718092205; cv=none; b=NHntA6s+XTUX2dNrEBFAv2wEgmFCfSybUzQRimUSVdtL7AqLocro6eDvHTzIHsRWqVnIQK7ThmLvju67Tq3yriA327Tf89A9y6u/N5e5EmLAFJ+q0ZNHRc6JPwk4rnEkQfwAC6mxtNWho55TAmPp0dV406AccE3pDpJ/ShHcJiU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718092205; c=relaxed/simple; bh=th9CP8dFoILsp10CMt+4CogoR9Emy+DQtuz9AQyf/ZI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lfN+PDr59l7h6LitWlxDVB2azpwi6p9g2CVCgykxyFNuYQUYlIIjITlo8k5EGY8s+GbSZ43O7QxHjD9EC8V8KW5maE8kCScBxwuyu6rO26gfV4uZsvqTfz0SgfgW1GfoJ/m8WCp+VUlAINVXNnQr5dxQS7qEGonZnTZFpqSaWbw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7D0E71688; Tue, 11 Jun 2024 00:50:27 -0700 (PDT) Received: from [10.162.41.16] (e116581.arm.com [10.162.41.16]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AAF473F64C; Tue, 11 Jun 2024 00:49:58 -0700 (PDT) Message-ID: <8918a555-1ed4-46da-bd63-4c5e324a9284@arm.com> Date: Tue, 11 Jun 2024 13:19:52 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] Add test to distinguish between thread's signal mask and ucontext_t To: shuah@kernel.org, oleg@redhat.com, stsp2@yandex.ru Cc: mingo@kernel.org, tglx@linutronix.de, mark.rutland@arm.com, ryan.roberts@arm.com, broonie@kernel.org, suzuki.poulose@arm.com, Anshuman.Khandual@arm.com, DeepakKumar.Mishra@arm.com, AneeshKumar.KizhakeVeetil@arm.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240611074307.812939-1-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20240611074307.812939-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sorry, please ignore this email thread; I am sending another one. On 6/11/24 13:13, Dev Jain wrote: > This patch series is motivated by the following observation: > > Raise a signal, jump to signal handler. The ucontext_t structure dumped > by kernel to userspace has a uc_sigmask field having the mask of blocked > signals. If you run a fresh minimalistic program doing this, this field > is empty, even if you block some signals while registering the handler > with sigaction(). > > Here is what the man-pages have to say: > > sigaction(2): "sa_mask specifies a mask of signals which should be blocked > (i.e., added to the signal mask of the thread in which the signal handler > is invoked) during execution of the signal handler. In addition, the > signal which triggered the handler will be blocked, unless the SA_NODEFER > flag is used." > > signal(7): Under "Execution of signal handlers", (1.3) implies: > > "The thread's current signal mask is accessible via the ucontext_t > object that is pointed to by the third argument of the signal handler." > > But, (1.4) states: > > "Any signals specified in act->sa_mask when registering the handler with > sigprocmask(2) are added to the thread's signal mask. The signal being > delivered is also added to the signal mask, unless SA_NODEFER was > specified when registering the handler. These signals are thus blocked > while the handler executes." > > There clearly is no distinction being made in the man pages between > "Thread's signal mask" and ucontext_t; this logically should imply > that a signal blocked by populating struct sigaction should be visible > in ucontext_t. > > Here is what the kernel code does (for Aarch64): > > do_signal() -> handle_signal() -> sigmask_to_save(), which returns > ¤t->blocked, is passed to setup_rt_frame() -> setup_sigframe() -> > __copy_to_user(). Hence, ¤t->blocked is copied to ucontext_t > exposed to userspace. Returning back to handle_signal(), > signal_setup_done() -> signal_delivered() -> sigorsets() and > set_current_blocked() are responsible for using information from > struct ksignal ksig, which was populated through the sigaction() > system call in kernel/signal.c: > copy_from_user(&new_sa.sa, act, sizeof(new_sa.sa)), > to update ¤t->blocked; hence, the set of blocked signals for the > current thread is updated AFTER the kernel dumps ucontext_t to > userspace. > > Assuming that the above is indeed the intended behaviour, because it > semantically makes sense, since the signals blocked using sigaction() > remain blocked only till the execution of the handler, and not in the > context present before jumping to the handler (but nothing can be > confirmed from the man-pages), the series introduces a test for > mangling with uc_sigmask. I will send a separate series to fix the > man-pages. > > The proposed selftest has been tested out on Aarch32, Aarch64 and x86_64. > > Changes in v2: > - Replace all occurrences of SIGPIPE with SIGSEGV > - Add a testcase: Raise the same signal again; it must not be queued > - Remove unneeded , > - Give a detailed test description in the comments; also describe the > exact meaning of delivered and blocked > - Handle errors for all libc functions/syscalls > - Mention tests in Makefile and .gitignore in alphabetical order > > Dev Jain (2): > selftests: Rename sigaltstack to generic signal > selftests: Add a test mangling with uc_sigmask > > tools/testing/selftests/Makefile | 2 +- > .../{sigaltstack => signal}/.gitignore | 3 +- > .../{sigaltstack => signal}/Makefile | 3 +- > .../current_stack_pointer.h | 0 > .../selftests/signal/mangle_uc_sigmask.c | 194 ++++++++++++++++++ > .../sas.c => signal/sigaltstack.c} | 0 > 6 files changed, 199 insertions(+), 3 deletions(-) > rename tools/testing/selftests/{sigaltstack => signal}/.gitignore (57%) > rename tools/testing/selftests/{sigaltstack => signal}/Makefile (53%) > rename tools/testing/selftests/{sigaltstack => signal}/current_stack_pointer.h (100%) > create mode 100644 tools/testing/selftests/signal/mangle_uc_sigmask.c > rename tools/testing/selftests/{sigaltstack/sas.c => signal/sigaltstack.c} (100%) >