linux-kernel - Re: [PATCH v10 3/8] powerpc: Move ima buffer functions to drivers/of/kexec.c

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Date:   Sat, 05 Dec 2020 16:48:56 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     zohar@...ux.ibm.com, robh@...nel.org, gregkh@...uxfoundation.org,
        james.morse@....com, catalin.marinas@....com, sashal@...nel.org,
        will@...nel.org, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, robh+dt@...nel.org, frowand.list@...il.com,
        vincenzo.frascino@....com, mark.rutland@....com,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        pasha.tatashin@...een.com, allison@...utok.net,
        kstewart@...uxfoundation.org, takahiro.akashi@...aro.org,
        tglx@...utronix.de, masahiroy@...nel.org, bhsharma@...hat.com,
        mbrugger@...e.com, hsinyi@...omium.org, tao.li@...o.com,
        christophe.leroy@....fr, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        prsriva@...ux.microsoft.com, balajib@...ux.microsoft.com
Subject: Re: [PATCH v10 3/8] powerpc: Move ima buffer functions to
 drivers/of/kexec.c


Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> writes:

> 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@...ux.microsoft.com>
> Signed-off-by: Prakhar Srivastava <prsriva@...ux.microsoft.com>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>

I'd personally squash this patch with the next one, but I'll leave it
just as a suggestion since maintainers are the ones who know best what
works well in this regard.

The code is good, except for a nit below:

Reviewed-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>

> ---
>  drivers/of/kexec.c    | 70 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/kexec.h |  3 ++
>  2 files changed, 73 insertions(+)
>
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index b7d59105fcb8..516b86f7113a 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -59,3 +59,73 @@ int delete_fdt_mem_rsv(void *fdt, unsigned long start, unsigned long size)
>  
>  	return -ENOENT;
>  }
> +
> +/**
> + * 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;
> +
> +	if (!IS_ENABLED(CONFIG_HAVE_IMA_KEXEC))
> +		return -EOPNOTSUPP;
> +
> +	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;
> +
> +	if (!IS_ENABLED(CONFIG_HAVE_IMA_KEXEC))
> +		return -EOPNOTSUPP;
> +
> +	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);
> +
> +	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/kexec.h b/include/linux/kexec.h
> index d0234c4815da..10ff704ab670 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -408,6 +408,9 @@ static inline int kexec_crash_loaded(void) { return 0; }
>  #endif /* CONFIG_KEXEC_CORE */
>  
>  #if defined(CONFIG_OF_FLATTREE)
> +extern int get_root_addr_size_cells(int *addr_cells, int *size_cells);
> +extern int get_ima_kexec_buffer(void *fdt, int chosen_node,
> +				unsigned long *addr, size_t *size);
>  extern int delete_fdt_mem_rsv(void *fdt, unsigned long start,
>  			      unsigned long size);
>  #endif /* CONFIG_OF_FLATTREE */

The extern keyword on function prototypes doesn't have any meaning.
It's better to drop them (I should have mentioned this on the previous
patch as well).

-- 
Thiago Jung Bauermann
IBM Linux Technology Center