On Fri, 2019-06-07 at 13:00 -0700, Dave Hansen wrote: > On 6/7/19 12:49 PM, Yu-cheng Yu wrote: > > > > > > This also gives us an excellent opportunity to make it read-only as seen > > > from > > > userspace to prevent exploits from just poking it full of ones before > > > redirecting execution. > > > > GLIBC sets bits only for legacy code, and then makes the bitmap read- > > only. That > > avoids most issues: > > > > To populate bitmap pages, mprotect() is required. > > Reading zero bitmap pages would not waste more physical memory, right? > > Huh, how does glibc know about all possible past and future legacy code > in the application? When dlopen() gets a legacy binary and the policy allows that, it will manage the bitmap: If a bitmap has not been created, create one. Set bits for the legacy code being loaded. Yu-cheng
