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

Thiago Jung Bauermann
2020-08-27T23:52:03Z

Lakshmi Ramasubramanian <nramas@linux.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