Re: [PATCH] kexec: Annotate struct crash_mem with __counted_by

Baoquan He
2023-09-23T00:46:54Z

On 09/22/23 at 10:52am, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct crash_mem.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: kexec@lists.infradead.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/linux/crash_core.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 3426f6eef60b..5126a4fecb44 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -131,7 +131,7 @@ static inline void __init reserve_crashkernel_generic(char *cmdline,
> struct crash_mem {
> unsigned int max_nr_ranges;
> unsigned int nr_ranges;
> - struct range ranges[];
> + struct range ranges[] __counted_by(max_nr_ranges);

This __counted_by() only makes sense when there's a obvious upper
boundary, max_nr_ranges in this case. This heavily depends and isn't
much in kernel? E.g struct swap_info_struct->avail_lists[]. Just
curious, not related to this patch though.

> };
>
> extern int crash_exclude_mem_range(struct crash_mem *mem,
> --
> 2.34.1
>