Re: [PATCH 2/3] powerpc: Fix undefined static key

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 16/08/2021 à 10:24, Joel Stanley a écrit :
> When CONFIG_PPC_BARRIER_NOSPEC=n, security.c is not built leading to a
> missing definition of uaccess_flush_key.
> 
>    LD      vmlinux.o
>    MODPOST vmlinux.symvers
>    MODINFO modules.builtin.modinfo
>    GEN     modules.builtin
>    LD      .tmp_vmlinux.kallsyms1
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/align.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/signal_64.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/process.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/traps.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/hw_breakpoint_constraints.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> powerpc64le-linux-gnu-ld: arch/powerpc/kernel/ptrace/ptrace.o:(.toc+0x0): more undefined references to `uaccess_flush_key' follow
> make[1]: *** [Makefile:1176: vmlinux] Error 1
> 
> Hack one in to fix the build.
> 
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
>   arch/powerpc/include/asm/security_features.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/security_features.h b/arch/powerpc/include/asm/security_features.h
> index 792eefaf230b..46ade7927a4c 100644
> --- a/arch/powerpc/include/asm/security_features.h
> +++ b/arch/powerpc/include/asm/security_features.h
> @@ -39,6 +39,9 @@ static inline bool security_ftr_enabled(u64 feature)
>   	return !!(powerpc_security_features & feature);
>   }
>   
> +#ifndef CONFIG_PPC_BARRIER_NOSPEC
> +DEFINE_STATIC_KEY_FALSE(uaccess_flush_key);
> +#endif

It will then be re-defined by each file that includes asm/security_features.h ....

You can't use a DEFINE_ in a .h

You have to fix the problem at its source.

Cleanest way I see it to modify asm/book3s/64/kup.h and something like

if (IS_ENABLED(CONFIG_PPC_BARRIER_NOSPEC) && static_branch_unlikely(&uaccess_flush_key)



>   
>   // Features indicating support for Spectre/Meltdown mitigations
>   
>