Re: [linux-next:master 2782/3950] kernel/bpf/helpers.c:1784:17: warning: argument 2 null where non-null expected because argument 3 is nonzero

[Jakub Sitnicki <jakub@cloudflare.com>]

On Thu, Aug 21, 2025 at 08:53 PM +08, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   7fa4d8dc380fbd81a9d702a855c50690c9c6442c
> commit: 6877cd392baecf816c2ba896a9d42874628004a5 [2782/3950] bpf: Enable
> read/write access to skb metadata through a dynptr
> config: sparc-randconfig-r063-20250821
> (https://download.01.org/0day-ci/archive/20250821/202508212031.ir9b3B6Q-lkp@intel.com/config)
> compiler: sparc-linux-gcc (GCC) 15.1.0
> reproduce (this is a W=1 build):
> (https://download.01.org/0day-ci/archive/20250821/202508212031.ir9b3B6Q-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202508212031.ir9b3B6Q-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>    kernel/bpf/helpers.c: In function '____bpf_snprintf':
>    kernel/bpf/helpers.c:1069:9: warning: function '____bpf_snprintf' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
>     1069 |         err = bstr_printf(str, str_size, fmt, data.bin_args);
>          |         ^~~
>    In function '__bpf_dynptr_read',
>        inlined from 'bpf_dynptr_copy' at kernel/bpf/helpers.c:2910:9:
>>> kernel/bpf/helpers.c:1784:17: warning: argument 2 null where non-null
>> expected because argument 3 is nonzero [-Wnonnull]
>     1784 | memmove(dst, bpf_skb_meta_pointer(src->data, src->offset + offset),
> len);
>          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    In file included from include/linux/string.h:65,
>                     from include/linux/bitmap.h:13,
>                     from include/linux/cpumask.h:12,
>                     from arch/sparc/include/asm/smp_32.h:15,
>                     from arch/sparc/include/asm/smp.h:7,
>                     from arch/sparc/include/asm/switch_to_32.h:5,
>                     from arch/sparc/include/asm/switch_to.h:7,
>                     from arch/sparc/include/asm/ptrace.h:120,
>                     from arch/sparc/include/asm/thread_info_32.h:19,
>                     from arch/sparc/include/asm/thread_info.h:7,
>                     from include/linux/thread_info.h:60,
>                     from include/asm-generic/preempt.h:5,
>                     from ./arch/sparc/include/generated/asm/preempt.h:1,
>                     from include/linux/preempt.h:79,
>                     from include/linux/alloc_tag.h:11,
>                     from include/linux/workqueue.h:9,
>                     from include/linux/bpf.h:10,
>                     from kernel/bpf/helpers.c:4:
>    arch/sparc/include/asm/string.h: In function 'bpf_dynptr_copy':
>    arch/sparc/include/asm/string.h:12:7: note: in a call to function 'memmove' declared 'nonnull_if_nonzero'
>       12 | void *memmove(void *, const void *, __kernel_size_t);
>          |       ^~~~~~~
>    In function '__bpf_dynptr_write',
>        inlined from 'bpf_dynptr_copy' at kernel/bpf/helpers.c:2913:9:
>    kernel/bpf/helpers.c:1845:17: warning: argument 1 null where non-null expected because argument 3 is nonzero [-Wnonnull]
>     1845 |                 memmove(bpf_skb_meta_pointer(dst->data, dst->offset + offset), src, len);
>          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    arch/sparc/include/asm/string.h: In function 'bpf_dynptr_copy':
>    arch/sparc/include/asm/string.h:12:7: note: in a call to function 'memmove'
> declared 'nonnull_if_nonzero'
>       12 | void *memmove(void *, const void *, __kernel_size_t);
>          |       ^~~~~~~
>
>
> vim +1784 kernel/bpf/helpers.c
>
>   1754	
>   1755	static int __bpf_dynptr_read(void *dst, u32 len, const struct bpf_dynptr_kern *src,
>   1756				     u32 offset, u64 flags)
>   1757	{
>   1758		enum bpf_dynptr_type type;
>   1759		int err;
>   1760	
>   1761		if (!src->data || flags)
>   1762			return -EINVAL;
>   1763	
>   1764		err = bpf_dynptr_check_off_len(src, offset, len);
>   1765		if (err)
>   1766			return err;
>   1767	
>   1768		type = bpf_dynptr_get_type(src);
>   1769	
>   1770		switch (type) {
>   1771		case BPF_DYNPTR_TYPE_LOCAL:
>   1772		case BPF_DYNPTR_TYPE_RINGBUF:
>   1773			/* Source and destination may possibly overlap, hence use memmove to
>   1774			 * copy the data. E.g. bpf_dynptr_from_mem may create two dynptr
>   1775			 * pointing to overlapping PTR_TO_MAP_VALUE regions.
>   1776			 */
>   1777			memmove(dst, src->data + src->offset + offset, len);
>   1778			return 0;
>   1779		case BPF_DYNPTR_TYPE_SKB:
>   1780 return __bpf_skb_load_bytes(src->data, src->offset + offset, dst, len);
>   1781		case BPF_DYNPTR_TYPE_XDP:
>   1782 return __bpf_xdp_load_bytes(src->data, src->offset + offset, dst, len);
>   1783		case BPF_DYNPTR_TYPE_SKB_META:
>> 1784 memmove(dst, bpf_skb_meta_pointer(src->data, src->offset + offset), len);
>   1785			return 0;
>   1786		default:
>   1787			WARN_ONCE(true, "bpf_dynptr_read: unknown dynptr type %d\n", type);
>   1788			return -EFAULT;
>   1789		}
>   1790	}
>   1791	

Right. This happens with CONFIG_NET=n.

I think in the end we need a simple wrapper around memmove to stub it
out with -EOPNOTSUPP when CONFIG_NET is disabled.