On Mon, Jun 10, 2019 at 1:43 PM Kees Cook <keescook@xxxxxxxxxxxx> 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.
