1) The user stack could be invalid. An invalid stack in the kernel will
cause the processor to double fault (see the recent double fault thread).
2) Security. You could set up the stack pointer from userspace so that
the kernel would overwrite memory that userspace can't access.
3) Security #2. You don't want to give userspace access to certain data
written to the stack in kernel mode.
-- Brian Gerst- 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/