Messages in this thread | | | Date | Tue, 18 Oct 2022 16:38:54 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH] x86/ibt: Implement FineIBT |
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On Tue, Oct 18, 2022 at 03:35:50PM +0200, Peter Zijlstra wrote: > > Implement an alternative CFI scheme that merges both the fine-grained > nature of kCFI but also takes full advantage of the coarse grained > hardware CFI as provided by IBT. > > To contrast: > > kCFI is a pure software CFI scheme and relies on being able to read > text -- specifically the instruction *before* the target symbol, and > does the hash validation *before* doing the call (otherwise control > flow is compromised already). > > FineIBT is a software and hardware hybrid scheme; by ensuring every > branch target starts with a hash validation it is possible to place > the hash validation after the branch. This has several advantages: > > o the (hash) load is avoided; no memop; no RX requirement. > > o IBT WAIT-FOR-ENDBR state is a speculation stop; by placing > the hash validation in the immediate instruction after > the branch target there is a minimal speculation window > and the whole is a viable defence against SpectreBHB. > > Obviously this patch relies on kCFI (upstream), but additionally it also > relies on the padding from the call-depth-tracking patches > (tip/x86/core). It uses this padding to place the hash-validation while > the call-sites are re-written to modify the indirect target to be 16 > bytes in front of the original target, thus hitting this new preamble.
Can the objtool changes be moved to a separate patch?
The RFC was 11 patches, is it now much smaller because of the new dependencies? The RFC had some eBPF changes and a test module, are those no longer needed?
-- Josh
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