linux-kernel - Re: [PATCH v4 2/5] powerpc: Use libfdt functions to fetch IMA buffer properties

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Message-ID: <8736478x7l.fsf@morokweng.localdomain>
Date:   Thu, 27 Aug 2020 20:50:54 -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 v4 2/5] powerpc: Use libfdt functions to fetch IMA
 buffer properties


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

> @@ -63,7 +29,22 @@ void remove_ima_buffer(void *fdt, int chosen_node)
>  	if (!prop)
>  		return;
>  
> -	ret = do_get_kexec_buffer(prop, len, &addr, &size);
> +	ret = fdt_address_cells(fdt, chosen_node);

This change was already present in the previous version of the patch but
it was just today that I noticed a problem: there's no #address-cells
property in /chosen. This code will still work though because if there's
no property this function returns 2 which is the correct value for
ppc64. But it's conceptually wrong. You need to pass the node offset for
/ so that it gets the #address-cells property from there.

> +	if (ret < 0)
> +		return;
> +	addr_cells = ret;
> +
> +	ret = fdt_size_cells(fdt, chosen_node);

Here we're not so lucky. The default value returned when no #size-cells
property is present is 1, which is wrong for ppc64 so this change
introduces a bug. You also need to pass the node offset for / here.

> +	if (ret < 0)
> +		return;
> +	size_cells = ret;
> +
> +	if (len < 4 * (addr_cells + size_cells))
> +		return;
> +
> +	addr = of_read_number(prop, addr_cells);
> +	size = of_read_number(prop + 4 * addr_cells, size_cells);
> +
>  	fdt_delprop(fdt, chosen_node, FDT_PROP_IMA_KEXEC_BUFFER);
>  	if (ret)
>  		return;
> @@ -129,9 +110,15 @@ int setup_ima_buffer(const struct kimage *image, void *fdt, int chosen_node)
>  	if (!image->arch.ima_buffer_size)
>  		return 0;
>  
> -	ret = get_addr_size_cells(&addr_cells, &size_cells);
> -	if (ret)
> +	ret = fdt_address_cells(fdt, chosen_node);
> +	if (ret < 0)
> +		return ret;
> +	addr_cells = ret;
> +
> +	ret = fdt_size_cells(fdt, chosen_node);
> +	if (ret < 0)
>  		return ret;
> +	size_cells = ret;
>  
>  	entry_size = 4 * (addr_cells + size_cells);

Ditto here.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center