Linux May Flip On Indirect Branch Tracking By Default (IBT)

[CKing123]

Not quite. Zen3 only supports Shadow Stack, not IBT. IBT support will arrive with Zen4

This is true. CET consists of two features: IBT and Shadow Stack in Zen 3. AMD only implements Shadow Stack. The reason likely is that there is a software version of this: CFI in GCC and LLVM and XFG (Windows) as they provide superior protection. IBT offers the weaker protection that CFG on Windows provides today but at lower overhead

[Jannik2099]

This is true. CET consists of two features: IBT and Shadow Stack in Zen 3. AMD only implements Shadow Stack. The reason likely is that there is a software version of this: CFI in GCC and LLVM and XFG (Windows) as they provide superior protection. IBT offers the weaker protection that CFG on Windows provides today but at lower overhead

GCC does not implement CFI, only Clang does.

[CKing123]

GCC does not implement CFI, only Clang does.

I stand corrected. So GCC has to rely on IBT for forward indirect branch protection it seems

[strtj]

I stand corrected. So GCC has to rely on IBT for forward indirect branch protection it seems

And you have to rely on your software to be compiled with that version of GCC.

[CKing123]

And you have to rely on your software to be compiled with that version of GCC.

I do wish that finer CFI be implemented in GCC, with IBT on x86 and BTI on arm64 be reserved in cases where the requirements of fine-grained CFI like LTO are not available. In addition, finer-grained CFI would work on all processors including older processors that don't support IBT. That said, Window's version of course-grained CFI called CFG works even on older processors and provides IBT/BTI level protection, while more fine-grained CFI is XFG (and Clang's CFI protection are comparable here). Perhaps GCC could implement CFG-like protection in cases where finer-grained protection is not available and processor does not support IBT/BTI for protection for all processors.

[CKing123]

Not quite. Zen3 only supports Shadow Stack, not IBT. IBT support will arrive with Zen4

This turned out not to be the case. Zen 4 continues to support Shadow Stack (as Zen 3 does), but does not include support for IBT