Re: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal stack overflow

[Bae, Chang Seok]

On May 11, 2021, at 11:36, Borislav Petkov <bp@xxxxxxxxx> wrote:
> 
> I clumsily tried to register a SIGSEGV handler with
> 
>        act.sa_sigaction = my_sigsegv;
>        sigaction(SIGSEGV, &act, NULL);
> 
> but that doesn't fire - task gets killed. Maybe I'm doing it wrong.

Since the altstack is already overflowed, perhaps set the flag like this -- not
using it to get the handler:

	act.sa_sigaction = my_sigsegv;
+	act.sa_flags = SA_SIGINFO;
	sigaction(SIGSEGV, &act, NULL);

FWIW, I think this is just a workaround for this case; in practice, altstack is
rather a backup for normal stack corruption.

Thanks,
Chang