Messages in this thread | | | Date | Tue, 14 Nov 2023 15:35:38 +0100 | Subject | Re: [PATCH v4 2/5] x86/alternative: add indirect call patching | From | Juergen Gross <> |
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On 14.11.23 15:18, Peter Zijlstra wrote: > 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 ?
ALT_FLAG_MAKE_CALL_DIRECT ?
> > I'm going to already raise my hand and say that's too long ;-)
I think the length of the name doesn't matter that much, as it is used only in the patching code and via the ALT_CALL() macro (at least as long as Boris doesn't ask me to change the macro name, too).
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |