----- On Jun 15, 2018, at 2:43 PM, Paul Burton paul.bur...@mips.com wrote: > Hi Mathieu, > > On Fri, Jun 15, 2018 at 01:41:25PM -0400, Mathieu Desnoyers wrote: >> > diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S >> > index 38a302919e6b..d7de8adcfcc8 100644 >> > --- a/arch/mips/kernel/entry.S >> > +++ b/arch/mips/kernel/entry.S >> > @@ -79,6 +79,10 @@ FEXPORT(ret_from_fork) >> > jal schedule_tail # a0 = struct task_struct *prev >> > >> > FEXPORT(syscall_exit) >> > +#ifdef CONFIG_DEBUG_RSEQ >> > + move a0, sp >> > + jal rseq_syscall >> > +#endif >> > local_irq_disable # make sure need_resched and >> > # signals dont change between >> > # sampling and return >> > @@ -141,6 +145,10 @@ work_notifysig: # deal >> > with pending signals and >> > j resume_userspace_check >> > >> > FEXPORT(syscall_exit_partial) >> > +#ifdef CONFIG_DEBUG_RSEQ >> > + move a0, sp >> > + jal rseq_syscall >> > +#endif >> > local_irq_disable # make sure need_resched doesn't >> > # change between and return >> > LONG_L a2, TI_FLAGS($28) # current->work >> >> Just to double-check: you did test with CONFIG_DEBUG_RSEQ=y, right ? > > Yes, I did. Although I only ran the selftests, which I don't believe > would actually trigger the SIGSEGV condition.
Yeah, I typically hand-craft a critical section that generate a system call in order to trigger this. It's hackish however, and only triggers the SIGSEGV on kernels with CONFIG_DEBUG_RSEQ=y. > > Side-note: maybe it'd be useful to have a test that does intentionally > perform a syscall within a restartable sequence & checks that it > actually receives a SIGSEGV?. We'd have to craft asm code for each architecture issuing a system call in a rseq c.s. to test this. And we'd need to make this test only runs on a kernel with CONFIG_DEBUG_RSEQ=y. I'm not convinced yet it's worth the effort to cleanly integrate this in selftests, but I'm very open to the idea. > >> Are there any live registers that need to be saved before calling >> rseq_syscall ? > > No - we just need gp/$28 & sp/$29, and the calling convention means > rseq_syscall() should return with those unmodified. Everything else that > we or userland care about is about to be loaded from the stack anyway. Sounds good! Thanks, Mathieu > > Thanks, > Paul -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
