On 8/26/25 6:34 PM, Nathan Chancellor wrote: > On Mon, Aug 25, 2025 at 03:31:34PM -0400, Kees Cook wrote: >> On August 25, 2025 1:00:22 PM EDT, Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> wrote: >>> On Mon, Aug 25, 2025 at 5:35 PM Kees Cook <kees@xxxxxxxxxx> wrote: >>>> >>>> Yeah, that's a good idea. What the right way to do that? >>>> >>>> config CFI_CLANG >>>> bool "Use Clang's Control Flow Integrity (CFI)" >>>> depends on ARCH_SUPPORTS_CFI >>>> select CFI >>>> >>>> ? >>> >>> I don't recall what is the idiomatic solution for renames, but I >>> remember Linus talking about this topic and about avoiding losing old >>> values if possible (perhaps getting a new question in `oldconfig` is >>> OK as long as the `olddefconfig` respects the old value). >>> >>> I think your suggestion above will still make it appear twice in >>> `menuconfig` -- there may be a way to play with visibility to make it >>> better. >>> >>> A simple possibility I can think of (assuming it works) is having the >>> CFI symbol for the time being introduced just as a `def_bool >>> CFI_CLANG` for a few releases so that people get the new one in their >>> configs. >> >> Ah, I think this works: >> >> config CFI_CLANG >> bool >> >> config CFI >> bool "...." >> default CFI_CLANG >> >> I will add that for v2. > > That does not appear to work for me. I applied > > diff --git a/arch/Kconfig b/arch/Kconfig > index c25a45d9aa96..0d3ed03c76c2 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -876,8 +876,12 @@ config ARCH_SUPPORTS_CFI > config ARCH_USES_CFI_TRAPS > bool > > +config CFI_CLANG > + bool > + > config CFI > bool "Use Kernel Control Flow Integrity (kCFI)" > + default CFI_CLANG > depends on ARCH_SUPPORTS_CFI > depends on $(cc-option,-fsanitize=kcfi) > help > > on top of this series and > > CONFIG_CFI_CLANG=y > # CONFIG_CFI_ICALL_NORMALIZE_INTEGERS is not set > # CONFIG_CFI_PERMISSIVE is not set > > gets turned into > > # CONFIG_CFI is not set > > after olddefconfig. CONFIG_CFI_CLANG has to be user selectable with a Could/did you test with 'oldconfig' instead? olddefconfig is going to use the default value from the Kconfig file, which if CFI_CLANG which is undefined/No/Not set. oldconfig will use the old value from the .config file. > prompt but the only solution I can think of at the moment results in a > duplicate prompt for Clang. > > diff --git a/arch/Kconfig b/arch/Kconfig > index c25a45d9aa96..93bf9b41a9de 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -876,8 +876,17 @@ config ARCH_SUPPORTS_CFI > config ARCH_USES_CFI_TRAPS > bool > > +config CFI_CLANG > + bool "Use Kernel Control Flow Integrity (kCFI) - Transitional" if CC_IS_CLANG > + select CFI > + depends on ARCH_SUPPORTS_CFI > + depends on $(cc-option,-fsanitize=kcfi) > + help > + This is a transitional symbol to CONFIG_CFI, see its help text > + for more information. > + > config CFI > - bool "Use Kernel Control Flow Integrity (kCFI)" > + bool "Use Kernel Control Flow Integrity (kCFI)" if CC_IS_GCC > depends on ARCH_SUPPORTS_CFI > depends on $(cc-option,-fsanitize=kcfi) > help > > Maybe that does not matter for the sake of keeping things working? > Otherwise, we could just keep things as they are with the patch set and > expect people to actually use oldconfig or diff the results of > olddefconfig (which I think is good practice anyways). > > Cheers, > Nathan > -- ~Randy
