Re: [Xen-devel] [PATCH v6 05/26] xen/arm: check for multiboot nodes only under /chosen

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 02/11/2018 23:44, Stefano Stabellini wrote:
> Make sure to only look for multiboot compatible nodes only under
> /chosen, not under any other paths (depth <= 3).
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
>
> ---
>
> Changes in v6:
> - do not proceed if fdt_get_path returns error != -FDT_ERR_NOSPACE
> - remove sizeof, use hardcoded value
>
> Changes in v5:
> - add patch
> - add check on return value of fdt_get_path
> ---
>   xen/arch/arm/bootfdt.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
> index 8eba42c..a42fe87 100644
> --- a/xen/arch/arm/bootfdt.c
> +++ b/xen/arch/arm/bootfdt.c
> @@ -173,7 +173,15 @@ static void __init process_multiboot_node(const void *fdt, 
> int node,
>       bootmodule_kind kind;
>       paddr_t start, size;
>       const char *cmdline;
> -    int len;
> +    int len = 8; /* sizeof "/chosen" */
> +    char path[8];
> +    int ret;
> +
> +    /* Check that the node is under "chosen" */
> +    ret = fdt_get_path(fdt, node, path, len);
> +    if ( (ret != 0 && ret != -FDT_ERR_NOSPACE) ||
I don't understand why you specifically check for -FDT_ERR_NOSPACE here.

Looking at fdt_get_path(...) there are case where the function may return 
-FDT_ERR_NOSPACE yet not filling up path. So you would end up to compare garbage.
> +         strncmp(path, "/chosen", len - 1) )
> +        return;
>   
>       prop = fdt_get_property(fdt, node, "reg", &len);
>       if ( !prop )
> @@ -286,8 +294,8 @@ static int __init early_scan_node(const void *fdt,
>   {
>       if ( device_tree_node_matches(fdt, node, "memory") )
>           process_memory_node(fdt, node, name, address_cells, size_cells);
> -    else if ( device_tree_node_compatible(fdt, node, "xen,multiboot-module" ) 
> ||
> -              device_tree_node_compatible(fdt, node, "multiboot,module" ))
> +    else if ( depth <= 3 && (device_tree_node_compatible(fdt, node, 
> "xen,multiboot-module" ) ||
> +              device_tree_node_compatible(fdt, node, "multiboot,module" )))
>           process_multiboot_node(fdt, node, name, address_cells, size_cells);
>       else if ( depth == 1 && device_tree_node_matches(fdt, node, "chosen") )
>           process_chosen_node(fdt, node, name, address_cells, size_cells);
Cheers,

--
Julien Grall

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