Message ID | 20240627035215.1527279-1-dev.jain@arm.com (mailing list archive) |
---|---|
Headers | show |
Series | Add test to distinguish between thread's signal mask and ucontext_t | expand |
On 6/27/24 09:22, 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. > > v3->v4: > - Allocate sigsets as automatic variables to avoid malloc() > > v2->v3: > - ucontext describes current state -> ucontext describes interrupted context > - Add a comment for blockage of USR2 even after return from handler > - Describe blockage of signals in a better way > > v1->v2: > - Replace all occurrences of SIGPIPE with SIGSEGV > - Fixed a mismatch between code comment and ksft log > - Add a testcase: Raise the same signal again; it must not be queued > - Remove unneeded <assert.h>, <unistd.h> > - 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 > > v1: > - https://lore.kernel.org/all/20240607122319.768640-1-dev.jain@arm.com/ > > 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 | 186 ++++++++++++++++++ > .../sas.c => signal/sigaltstack.c} | 0 > 6 files changed, 191 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%) If everything is fine, can this patchset be pulled? Thanks. >