Re: [tip: x86/core] x86/ibt: Implement FineIBT-BHI mitigation

Peter Zijlstra
2025-03-10T08:55:42Z

Ping -- anything I can do the help?

On Wed, Feb 26, 2025 at 08:53:08PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 26, 2025 at 12:54:35PM -0000, tip-bot2 for Peter Zijlstra wrote:
>
> > diff --git a/Makefile b/Makefile
> > index 96407c1..f19431f 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1014,6 +1014,9 @@ CC_FLAGS_CFI := -fsanitize=kcfi
> > ifdef CONFIG_CFI_ICALL_NORMALIZE_INTEGERS
> > CC_FLAGS_CFI += -fsanitize-cfi-icall-experimental-normalize-integers
> > endif
> > +ifdef CONFIG_FINEIBT_BHI
> > + CC_FLAGS_CFI += -fsanitize-kcfi-arity
> > +endif
> > ifdef CONFIG_RUST
> > # Always pass -Zsanitizer-cfi-normalize-integers as CONFIG_RUST selects
> > # CONFIG_CFI_ICALL_NORMALIZE_INTEGERS.
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index c4175f4..5c27726 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -2473,6 +2473,10 @@ config CC_HAS_RETURN_THUNK
> > config CC_HAS_ENTRY_PADDING
> > def_bool $(cc-option,-fpatchable-function-entry=16,16)
> >
> > +config CC_HAS_KCFI_ARITY
> > + def_bool $(cc-option,-fsanitize=kcfi -fsanitize-kcfi-arity)
> > + depends on CC_IS_CLANG && !RUST
> > +
>
> Miguel, can we work on fixing that !RUST dep?
>
> > config FUNCTION_PADDING_CFI
> > int
> > default 59 if FUNCTION_ALIGNMENT_64B
> > @@ -2498,6 +2502,10 @@ config FINEIBT
> > depends on X86_KERNEL_IBT && CFI_CLANG && MITIGATION_RETPOLINE
> > select CALL_PADDING
> >
> > +config FINEIBT_BHI
> > + def_bool y
> > + depends on FINEIBT && CC_HAS_KCFI_ARITY
> > +
> > config HAVE_CALL_THUNKS
> > def_bool y
> > depends on CC_HAS_ENTRY_PADDING && MITIGATION_RETHUNK && OBJTOOL