Re: [PATCH 20/23] x86, kaiser: add a function to check for KAISER being enabled

Eduardo Valentin
2017-11-25T01:23:11Z

On Wed, Nov 22, 2017 at 04:35:18PM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> Currently, all of the checks for KAISER are compile-time checks.
>
> Runtime checks are needed for turning it on/off at runtime.
>
> Add a function to do that.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
> Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
> Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
> Cc: Richard Fellner <richard.fellner@student.tugraz.at>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Kees Cook <keescook@google.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: x86@kernel.org
> ---
>
> b/arch/x86/include/asm/kaiser.h | 5 +++++
> b/include/linux/kaiser.h | 5 +++++
> 2 files changed, 10 insertions(+)
>
> diff -puN arch/x86/include/asm/kaiser.h~kaiser-dynamic-check-func arch/x86/include/asm/kaiser.h
> --- a/arch/x86/include/asm/kaiser.h~kaiser-dynamic-check-func 2017-11-22 15:45:55.262619723 -0800
> +++ b/arch/x86/include/asm/kaiser.h 2017-11-22 15:45:55.267619723 -0800
> @@ -56,6 +56,11 @@ extern void kaiser_remove_mapping(unsign
> */
> extern void kaiser_init(void);
>
> +static inline bool kaiser_active(void)
> +{
> + extern int kaiser_enabled;

Should this really be extern ?

I am getting a compilation error while linking the bzImage with this series:
arch/x86/boot/compressed/pagetable.o: In function `kernel_ident_mapping_init':
pagetable.c:(.text+0x336): undefined reference to `kaiser_enabled'
arch/x86/boot/compressed/Makefile:109: recipe for target 'arch/x86/boot/compressed/vmlinux' failed
make[2]: *** [arch/x86/boot/compressed/vmlinux] Error 1
arch/x86/boot/Makefile:112: recipe for target 'arch/x86/boot/compressed/vmlinux' failed
make[1]: *** [arch/x86/boot/compressed/vmlinux] Error 2
arch/x86/Makefile:296: recipe for target 'bzImage' failed
make: *** [bzImage] Error 2

What I did was to remove the extern and EXPORT_SYMBOL(kaiser_enabled) and initialize kaiser_enabled as 0, after that I got a proper bzImage.

> + return kaiser_enabled;
> +}
> #endif
>
> #endif /* __ASSEMBLY__ */
> diff -puN include/linux/kaiser.h~kaiser-dynamic-check-func include/linux/kaiser.h
> --- a/include/linux/kaiser.h~kaiser-dynamic-check-func 2017-11-22 15:45:55.264619723 -0800
> +++ b/include/linux/kaiser.h 2017-11-22 15:45:55.268619723 -0800
> @@ -28,5 +28,10 @@ static inline int kaiser_add_mapping(uns
> static inline void kaiser_add_mapping_cpu_entry(int cpu)
> {
> }
> +
> +static inline bool kaiser_active(void)
> +{
> + return 0;
> +}
> #endif /* !CONFIG_KAISER */
> #endif /* _INCLUDE_KAISER_H */
> _
>

--
All the best,
Eduardo Valentin