Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 13 Jun 2019 12:08:38 -0700 | Subject | Re: [PATCH 2/5] x86/vsyscall: Add a new vsyscall=xonly mode |
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On Mon, Jun 10, 2019 at 1:43 PM Kees Cook <keescook@chromium.org> wrote: > > On Mon, Jun 10, 2019 at 01:25:28PM -0700, Andy Lutomirski wrote: > > With vsyscall emulation on, we still expose a readable vsyscall page > > that contains syscall instructions that validly implement the > > vsyscalls. We need this because certain dynamic binary > > instrumentation tools attempt to read the call targets of call > > instructions in the instrumented code. If the instrumented code > > uses vsyscalls, then the vsyscal page needs to contain readable > > code. > > > > Unfortunately, leaving readable memory at a deterministic address > > can be used to help various ASLR bypasses, so we gain some hardening > > value if we disallow vsyscall reads. > > > > Given how rarely the vsyscall page needs to be readable, add a > > mechanism to make the vsyscall page be execute only. > > Should the commit log mention that the VVAR portion goes away under > xonly? (Since it's not executable.)
No, because vsyscall VVAR is long gone no matter what. Even the old vsyscall=native didn't have it.
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