Re: PowerPC paxtest results w/ gcc-4.1

Albert Cahalan writes:

VM_STACK_DEFAULT_FLAGS32 is wrong. A fail-safe
default is important for security. If gcc on PowerPC ever
does generate code which puts trampolines on the stack,
then that can be fixed by converting to legal C code or
by adding the fragile marking to the defective executables.
Did gcc ever generate such code on PowerPC? If not,
then there is no reason to ever allow an executable stack.

I believe it did for nested procedures in C.

Now that we have the VDSO and use it for signal trampolines, we
probably could change the default stack protections.

No. Look in the segment registers. The granularity
isn't great, but the stack can be protected at least.

No, ld.so tends to go just below the stack:

f7fe6000-f7fff000 r-xp 00000000 08:05 17069          /lib/ld-2.3.6.so
f800e000-f800f000 r--p 00018000 08:05 17069          /lib/ld-2.3.6.so
f800f000-f8010000 rwxp 00019000 08:05 17069          /lib/ld-2.3.6.so
ffe67000-ffe7c000 rw-p ffe67000 00:00 0              [stack]

Paul.