On 9/9/2020 3:59 PM, Dave Hansen wrote:
On 9/9/20 3:08 PM, Yu, Yu-cheng wrote:
After looking at this more, I found the changes are more similar to
mprotect() than madvise(). We are going to change an anonymous mapping
to a read-only mapping, and add the VM_SHSTK flag to it. Would an
x86-specific mprotect(PROT_SHSTK) make more sense?
One alternative would be requiring a read-only mapping for
madvise(MADV_SHSTK). But that is inconvenient for the application.
Why? It's just:
mmap()/malloc();
mprotect(PROT_READ);
madvise(MADV_SHSTK);
vs.
mmap()/malloc();
mprotect(PROT_SHSTK);
I'm not sure a single syscall counts as inconvenient.
I don't quite think we should use a PROT_ bit for this. It seems like
the kind of thing that could be fragile and break existing expectations.
I don't care _that_ strongly though.
What if a writable mapping is passed to madvise(MADV_SHSTK)? Should
that be rejected?
