Messages in this thread | | | Subject | Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function | From | Yu-cheng Yu <> | Date | Fri, 07 Jun 2019 13:06:10 -0700 |
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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
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