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 <202301061234.D15CF0E627@keescook>
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From:   Julius Werner <jwerner@chromium.org>
Date:   Fri, 6 Jan 2023 23:27:04 +0100
Message-ID: <CAODwPW9bM8+V+JphjpNHS9YRmb+AXNQUi+VRjORkGZP6gY=ynA@mail.gmail.com>
Subject: Re: [PATCH] firmware: coreboot: Check size of table entry and split memcpy
To:     Kees Cook <keescook@chromium.org>
Cc:     Julius Werner <jwerner@chromium.org>,
        Jack Rosenthal <jrosenth@chromium.org>,
        Paul Menzel <pmenzel@molgen.mpg.de>,
        Guenter Roeck <groeck@chromium.org>,
        Brian Norris <briannorris@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
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Precedence: bulk

Yeah, exactly. Isn't that a bit simpler? (I wasn't aware of the
flexible array member in union issue, but it sounds like we have a
neat solution for that already.)

On Fri, Jan 6, 2023 at 9:35 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Jan 06, 2023 at 04:03:35PM +0100, Julius Werner wrote:
> > Have you considered adding the flexible array member directly to the
> > union in struct coreboot_device instead? I think that would make this
> > a bit simpler by not having to copy header and data portion
> > separately.
>
> Are you thinking something like this?
>
>
> diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
> index 2652c396c423..564a3c908838 100644
> --- a/drivers/firmware/google/coreboot_table.c
> +++ b/drivers/firmware/google/coreboot_table.c
> @@ -93,14 +93,19 @@ static int coreboot_table_populate(struct device *dev, void *ptr)
>         for (i = 0; i < header->table_entries; i++) {
>                 entry = ptr_entry;
>
> -               device = kzalloc(sizeof(struct device) + entry->size, GFP_KERNEL);
> +               if (entry->size < sizeof(*entry)) {
> +                       dev_warn(dev, "coreboot table entry too small!\n");
> +                       return -EINVAL;
> +               }
> +
> +               device = kzalloc(sizeof(device->dev) + entry->size, GFP_KERNEL);
>                 if (!device)
>                         return -ENOMEM;
>
>                 device->dev.parent = dev;
>                 device->dev.bus = &coreboot_bus_type;
>                 device->dev.release = coreboot_device_release;
> -               memcpy(&device->entry, ptr_entry, entry->size);
> +               memcpy(device->raw, entry, entry->size);
>
>                 switch (device->entry.tag) {
>                 case LB_TAG_CBMEM_ENTRY:
> diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
> index 37f4d335a606..d814dca33a08 100644
> --- a/drivers/firmware/google/coreboot_table.h
> +++ b/drivers/firmware/google/coreboot_table.h
> @@ -79,6 +79,7 @@ struct coreboot_device {
>                 struct lb_cbmem_ref cbmem_ref;
>                 struct lb_cbmem_entry cbmem_entry;
>                 struct lb_framebuffer framebuffer;
> +               DECLARE_FLEX_ARRAY(u8, raw);
>         };
>  };
>
>
> --
> Kees Cook