Messages in this thread | | | Date | Tue, 14 Nov 2023 15:18:33 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 2/5] x86/alternative: add indirect call patching |
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On Tue, Nov 14, 2023 at 02:47:15PM +0100, Borislav Petkov wrote: > On Tue, Nov 14, 2023 at 01:50:28PM +0100, Peter Zijlstra wrote: > > This loads the function target from the pv_ops table. We can't otherwise > > do this. > > On Tue, Nov 14, 2023 at 01:56:37PM +0100, Juergen Gross wrote: > > It is replacing an _indirect_ call with a _direct_ one, taking the > > call target from the pointer used by the indirect call. > > Then this is not just a ALT_FLAG_CALL. This is something special. The > flag definition needs a better name along with an explanation what it > does, perhaps best with an example from the final vmlinux - not from the > object file: > > call *0x0(%rip) > > ==> > > call *0x0 > > where the offsets haven't been linked in yet.
Well, a random absolute address isn't going to be any better or worse than 0. But perhaps adding the relocation as a comment helps?
ff 15 00 00 00 00 call *0x0(%rip) # R_X86_64_PC32 pv_ops+0x4 into: e8 00 00 00 00 90 call +0 # R_X86_64_PC32 *(pv_ops+0x04)
> If this is going into the generic infrastructure, then it better be > explained properly so that other stuff can potentially use it too.
ALT_FLAG_DEREFERENCE_INDIRECT_CALL ?
I'm going to already raise my hand and say that's too long ;-)
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