On Fri, Dec 13, 2019 at 05:43:15PM -0800, Peter Collingbourne wrote:
> On Wed, Dec 11, 2019 at 10:44 AM Catalin Marinas
> <catalin.marinas@xxxxxxx> wrote:
> > diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> > index dd2cdc0d5be2..41fae64af82a 100644
> > --- a/arch/arm64/kernel/signal.c
> > +++ b/arch/arm64/kernel/signal.c
> > @@ -730,6 +730,9 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
> > regs->regs[29] = (unsigned long)&user->next_frame->fp;
> > regs->pc = (unsigned long)ka->sa.sa_handler;
> >
> > + /* TCO (Tag Check Override) always cleared for signal handlers */
> > + regs->pstate &= ~PSR_TCO_BIT;
> > +
> > if (ka->sa.sa_flags & SA_RESTORER)
> > sigtramp = ka->sa.sa_restorer;
> > else
> > @@ -921,6 +924,11 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
> > if (thread_flags & _TIF_UPROBE)
> > uprobe_notify_resume(regs);
> >
> > + if (thread_flags & _TIF_MTE_ASYNC_FAULT) {
> > + clear_thread_flag(TIF_MTE_ASYNC_FAULT);
> > + force_signal_inject(SIGSEGV, SEGV_MTEAERR, 0);
>
> In the case where the kernel is entered due to a syscall, this will
> inject a signal, but only after servicing the syscall. This means
> that, for example, if the syscall is exit(), the async tag check
> failure will be silently ignored. I can reproduce the problem with the
> program below:
[...]
> This patch fixes the problem for me:
>
> diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> index 9a9d98a443fc..d0c8918dee00 100644
> --- a/arch/arm64/kernel/syscall.c
> +++ b/arch/arm64/kernel/syscall.c
> @@ -94,6 +94,8 @@ static void el0_svc_common(struct pt_regs *regs, int
> scno, int sc_nr,
> const syscall_fn_t syscall_table[])
> {
> unsigned long flags = current_thread_info()->flags;
> + if (flags & _TIF_MTE_ASYNC_FAULT)
> + return;
It needs a bit of thinking. This one wouldn't work if you want to handle
the signal and resume since it would skip the SVC instruction. We'd need
at least to do a regs->pc -= 4 and probably move it further down in this
function.
--
Catalin
