| Date | Fri, 18 Mar 2022 11:49:58 +0100 | From | Peter Zijlstra <> | Subject | Re: [tip: x86/core] objtool: Find unused ENDBR instructions |
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On Thu, Mar 17, 2022 at 03:22:54PM -0700, Josh Poimboeuf wrote: > On Tue, Mar 15, 2022 at 03:39:52PM +0000, David Laight wrote: > > From: Peter Zijlstra > > > > > > objtool: Find unused ENDBR instructions > > > > > > Find all ENDBR instructions which are never referenced and stick them > > > in a section such that the kernel can poison them, sealing the > > > functions from ever being an indirect call target. > > > > Thought, what happens if the only indirect call is from > > code in a module? > > Then <boom>, I guess. Is it safe to assume in-tree modules don't need > to do indirect calls to exported functions? I guess we'll find out :-)
So exported functions will keep their ENDBR. Specifically, their address is taken by the EXPORT_SYMBOL thing.
Sealing them might work, but let's not do that just now ;-)
Any unexported function discovered through kallsyms OTOH... those deservedly will go *boom*.
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