If I read that paper correctly, my patch should not break this
specific design. In fact, it explicitly states the possibility of an
equivalent of my patch: "the signal handler scope is often just a flag
in the process control block (PCB) ..."
As Linus pointed out, there might be other cases though.
> My Pine's 'd' key deleted his patch before I could take an exhaustive
> look, but it should be fine though. They both do use to enter the signal
> handler simply to get a snapshot of the context, and they exit the handler
> by letting the kernel to clean the on-sig-stack flag. try to search
> archives to take a better look at the patch ...
The patches are small, so read below for convenience.
Jörn
-- It's just what we asked for, but not what we want! -- anonymous--- linux-2.5.73/include/linux/sched.h~ss_generic 2003-07-04 18:57:01.000000000 +0200 +++ linux-2.5.73/include/linux/sched.h 2003-07-04 18:59:03.000000000 +0200 @@ -480,6 +480,7 @@ #define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */ #define PF_KSWAPD 0x00040000 /* I am kswapd */ #define PF_SWAPOFF 0x00080000 /* I am in swapoff */ +#define PF_SS_ACTIVE 0x00100000 /* Executing on signal stack now */ #define PF_LESS_THROTTLE 0x01000000 /* Throttle me less: I clena memory */ #ifdef CONFIG_SMP
--- linux-2.5.73/arch/i386/kernel/signal.c~ss_i386 2003-07-04 18:57:01.000000000 +0200 +++ linux-2.5.73/arch/i386/kernel/signal.c 2003-07-04 18:59:04.000000000 +0200 @@ -181,6 +181,9 @@ } } + if (sas_ss_flags(regs->esp) == 0) + current->flags &= ~PF_SS_ACTIVE; + err |= __get_user(*peax, &sc->eax); return err; @@ -317,9 +320,22 @@ esp = regs->esp; /* This is the X/Open sanctioned signal stack switching. */ - if (ka->sa.sa_flags & SA_ONSTACK) { - if (sas_ss_flags(esp) == 0) - esp = current->sas_ss_sp + current->sas_ss_size; + if ((ka->sa.sa_flags & SA_ONSTACK) && (sas_ss_flags(esp) == 0)) { + /* If we have switches to the signal stack before, + * something bad has happened to it, asking for a + * segmentation fault. + * If not, remember it for the next time + */ + if (current->flags & PF_SS_ACTIVE) { + ka->sa.sa_handler = SIG_DFL; + force_sig(SIGSEGV, current); + /* XXX would it be simpler to return some broken + * value like NULL and have the calling function + * signal the segv? + */ + } + current->flags |= PF_SS_ACTIVE; + esp = current->sas_ss_sp + current->sas_ss_size; } /* This is the legacy signal stack switching. */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/