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Date: Mon, 16 Oct 2023 22:46:37 -0700
From: Eric Biggers <ebiggers@kernel.org>
To: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org, fsverity@lists.linux.dev, ast@kernel.org,
	daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org,
	kernel-team@meta.com, tytso@mit.edu, roberto.sassu@huaweicloud.com
Subject: Re: [PATCH bpf-next 2/5] bpf, fsverity: Add kfunc
 bpf_get_fsverity_digest
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On Mon, Oct 16, 2023 at 10:35:16PM -0700, Song Liu wrote:
> On Mon, Oct 16, 2023 at 8:12 PM Eric Biggers <ebiggers@kernel.org> wrote:
> >
> > On Mon, Oct 16, 2023 at 01:10:40PM -0700, Song Liu wrote:
> > > On Sun, Oct 15, 2023 at 12:07 AM Eric Biggers <ebiggers@kernel.org> wrote:
> > > >
> > > [...]
> > > > > + */
> > > > > +__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr)
> > > > > +{
> > > > > +     const struct inode *inode = file_inode(file);
> > > > > +     struct fsverity_digest *arg = digest_ptr->data;
> > > >
> > > > What alignment is guaranteed here?
> > >
> > > drnptr doesn't not provide alignment guarantee for digest_ptr->data.
> > > If we need alignment guarantee, we need to add it here.
> >
> > So technically it's wrong to cast it to struct fsverity_digest, then.
> 
> We can enforce alignment here. Would __aligned(2) be sufficient?
> 

Do you mean something like the following:

	if (!IS_ALIGNED((uintptr_t)digest_ptr->data, __alignof__(*arg)))
		return -EINVAL;