Re: [PATCH v11 2/8] powerpc: Move ima buffer functions to drivers/of/kexec.c

[Lakshmi Ramasubramanian]

On 12/15/20 10:16 AM, Rob Herring wrote:
> On Mon, Dec 14, 2020 at 11:18:48AM -0800, Lakshmi Ramasubramanian wrote:
> > The functions do_get_kexec_buffer() and get_addr_size_cells(),
> > defined in arch/powerpc/kexec/ima.c, retrieve the address and size
> > of the given property from the device tree blob. These functions do
> > not have architecture specific code, but are currently limited to
> > powerpc. do_get_kexec_buffer() correctly handles a device tree property
> > that is a child node of the root node, but not anything other than
> > the immediate root child nodes.
> >
> > Move architecture independent functions get_ima_kexec_buffer() and
> > get_root_addr_size_cells() to "drivers/of/kexec.c". These functions
> > retrieve the chosen node "linux,ima-kexec-buffer" from the device tree,
> > and return the address and size of the buffer used for carrying forward
> > the IMA measurement log across kexec system call.
> >
> > Co-developed-by: Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/of/kexec.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++
> >   include/linux/of.h |  3 ++
> >   2 files changed, 71 insertions(+)
> >
> > diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> > index 66787be081fe..9af5371340b1 100644
> > --- a/drivers/of/kexec.c
> > +++ b/drivers/of/kexec.c
> > @@ -30,6 +30,10 @@
> >   /**
> >    * fdt_find_and_del_mem_rsv - delete memory reservation with given address and size
> >    *
> > + * @fdt: Flattened Device Tree to update
> > + * @start: Starting address of the reservation to delete
> > + * @size: Size of the reservation to delete
> > + *
>
> This belongs in the patch adding fdt_find_and_del_mem_rsv.

Yes.

> >    * Return: 0 on success, or negative errno on error.
> >    */
> >   static int fdt_find_and_del_mem_rsv(void *fdt, unsigned long start, unsigned long size)
> > @@ -226,3 +230,67 @@ int of_kexec_setup_new_fdt(const struct kimage *image, void *fdt,
> >   
> >   	return 0;
> >   }
> > +
> > +/**
> > + * get_root_addr_size_cells - Get address and size of root node
> > + *
> > + * @addr_cells: Return address of the root node
> > + * @size_cells: Return size of the root node
> > + *
> > + * Return: 0 on success, or negative errno on error.
> > + */
> > +int get_root_addr_size_cells(int *addr_cells, int *size_cells)
> > +{
> > +	struct device_node *root;
> > +
> > +	root = of_find_node_by_path("/");
> > +	if (!root)
> > +		return -EINVAL;
> > +
> > +	*addr_cells = of_n_addr_cells(root);
> > +	*size_cells = of_n_size_cells(root);
> > +
> > +	of_node_put(root);
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * get_ima_kexec_buffer - Get address and size of IMA kexec buffer
> > + *
> > + * @fdt: Flattened Device Tree
> > + * @chosen_node: Offset of chosen node in the FDT
> > + * @addr: Return address of the node
> > + * @size: Return size of the node
> > + *
> > + * Return: 0 on success, or negative errno on error.
> > + */
> > +int get_ima_kexec_buffer(void *fdt, int chosen_node,
> > +			 unsigned long *addr, size_t *size)
> > +{
> > +	const void *prop;
> > +	int addr_cells, size_cells, prop_len;
> > +	int rc;
> > +
> > +	rc = get_root_addr_size_cells(&addr_cells, &size_cells);
> > +	if (rc)
> > +		return rc;
> > +
> > +	if (fdt)
> > +		prop = fdt_getprop(fdt, chosen_node,
> > +				   "linux,ima-kexec-buffer", &prop_len);
> > +	else
> > +		prop = of_get_property(of_chosen,
> > +				       "linux,ima-kexec-buffer", &prop_len);
>
> This is an odd structure. The DT APIs are generally of_foo() for
> unflattened tree and of_flat_foo() for FDT.
Ok - will update.

> > +
> > +	if (!prop)
> > +		return -ENOENT;
> > +
> > +	if (prop_len < 4 * (addr_cells + size_cells))
> > +		return -EINVAL;
> > +
> > +	*addr = of_read_number(prop, addr_cells);
> > +	*size = of_read_number(prop + 4 * addr_cells, size_cells);
> > +
> > +	return 0;
> > +}
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index 3375f5295875..fb2ef274135d 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -562,6 +562,9 @@ struct kimage;
> >   int of_kexec_setup_new_fdt(const struct kimage *image, void *fdt,
> >   			   unsigned long initrd_load_addr, unsigned long initrd_len,
> >   			   const char *cmdline);
> > +int get_root_addr_size_cells(int *addr_cells, int *size_cells);
> > +int get_ima_kexec_buffer(void *fdt, int chosen_node,
> > +			 unsigned long *addr, size_t *size);
>
> The whole point of moving code out of arch code was to avoid all these
> cross tree calls.
>
> I was expecting the next step to be moving setup_ima_buffer() call into
> of_kexec_setup_new_fdt with all the code in powerpc/kexec/ima.c moved
> here. Then the end result to enable on arm64 is just selecting
> HAVE_IMA_KEXEC and adding fields to kimage_arch.

setup_ima_buffer() implemented for powerpc can be simplified by using
fdt_appendprop_addrrange() to add the IMA buffer's address and size to 
"linux,ima-kexec-buffer" node. With that change, setup_ima_buffer() can 
be moved into of_kexec_setup_new_fdt along with all the code in 
powerpc/kexec/ima.c to drivers'of/kexec.c

I'll make the above change and post the next version shortly.

thanks,
 -lakshmi