Re: [PATCH v3 5/8] xen/hypfs: add support for id-based dynamic directories

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.12.2020 17:09, Juergen Gross wrote:
> +static const struct hypfs_entry *hypfs_dyndir_enter(
> +    const struct hypfs_entry *entry)
> +{
> +    const struct hypfs_dyndir_id *data;
> +
> +    data = hypfs_get_dyndata();
> +
> +    /* Use template with original enter function. */
> +    return data->template->e.funcs->enter(&data->template->e);
> +}

At the example of this (applies to other uses as well): I realize
hypfs_get_dyndata() asserts that the pointer is non-NULL, but
according to the bottom of ./CODING_STYLE this may not be enough
when considering the implications of a NULL deref in the context
of a PV guest. Even this living behind a sysctl doesn't really
help, both because via XSM not fully privileged domains can be
granted access, and because speculation may still occur all the
way into here. (I'll send a patch to address the latter aspect in
a few minutes.) While likely we have numerous existing examples
with similar problems, I guess in new code we'd better be as
defensive as possible.

> +/*
> + * Fill dyndata with a dynamically generated directory based on a template
> + * and a numerical id.
> + * Needs to be kept in sync with hypfs_read_dyndir_id_entry() regarding the
> + * name generated.
> + */
> +struct hypfs_entry *hypfs_gen_dyndir_id_entry(
> +    const struct hypfs_entry_dir *template, unsigned int id, void *data)
> +{

s/directory/entry/ in the comment (and as a I realize only now
then also for hypfs_read_dyndir_id_entry())?

Jan