Re: [PATCH v2 6/7] percpu: Add __alloc_size attributes for better bounds checking

[Dennis Zhou]

Hello,

On Wed, Aug 18, 2021 at 02:40:20PM -0700, Kees Cook wrote:
> As already done in GrapheneOS, add the __alloc_size attribute for
> appropriate percpu allocator interfaces, to provide additional hinting
> for better bounds checking, assisting CONFIG_FORTIFY_SOURCE and other
> compiler optimizations.

Can you elaborate a little bit for me how this works for percpu? In any
case that's not uniprocessor, any modification is done through address
accessors and not on the returned percpu pointer. Is the metadata kept
by gcc/clang able to transpire the percpu pointer accessors?

Thanks,
Dennis

> 
> Co-developed-by: Daniel Micay <danielmicay@xxxxxxxxx>
> Signed-off-by: Daniel Micay <danielmicay@xxxxxxxxx>
> Cc: Dennis Zhou <dennis@xxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  include/linux/percpu.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 5e76af742c80..119f41815b32 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -123,6 +123,7 @@ extern int __init pcpu_page_first_chunk(size_t reserved_size,
>  				pcpu_fc_populate_pte_fn_t populate_pte_fn);
>  #endif
>  
> +__alloc_size(1)
>  extern void __percpu *__alloc_reserved_percpu(size_t size, size_t align);
>  extern bool __is_kernel_percpu_address(unsigned long addr, unsigned long *can_addr);
>  extern bool is_kernel_percpu_address(unsigned long addr);
> @@ -131,7 +132,9 @@ extern bool is_kernel_percpu_address(unsigned long addr);
>  extern void __init setup_per_cpu_areas(void);
>  #endif
>  
> +__alloc_size(1)
>  extern void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp);
> +__alloc_size(1)
>  extern void __percpu *__alloc_percpu(size_t size, size_t align);
>  extern void free_percpu(void __percpu *__pdata);
>  extern phys_addr_t per_cpu_ptr_to_phys(void *addr);
> -- 
> 2.30.2
>