Messages in this thread | | | Date | Tue, 18 Oct 2022 22:30:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/ibt: Implement FineIBT |
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On Tue, Oct 18, 2022 at 01:17:28PM -0700, Joao Moreira wrote: > > > > > Tangent: why are these nop instead of 0xcc? These bytes aren't > > > executed > > > ever are they? > > > > Because that's what the compiler gets us through > > -fpatchable-function-entry. > > Is it useful to get the compiler to emit 0xcc with > -fpatchable-function-entry under any circumstance? I can probably change > that quickly if needed/useful.
Having it emit 0xcc for the bytes in front of the symbol might be interesting. It would mean a few kernel changes, but nothing too hard.
That is, -fpatchable-function-entry=N,M gets us N-M bytes in at the start of the symbol and M bytes in front of it. The N-M bytes at the start of the function *are* executed and should obviously not become 0xcc (GCC keeps them 0x90 while LLVM makes them large NOPs).
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