Re: [PATCH] libfdt: Add FDT alignment check to fdt_check_header()

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Tue, Apr 06, 2021 at 02:07:12PM -0500, Rob Herring wrote:
> Only checking the FDT alignment in fdt_ro_probe_() means that
> fdt_check_header() can pass, but then subsequent API calls fail on
> alignment checks. Let's add an alignment check to fdt_check_header() so
> alignment errors are found up front.
> 
> Cc: Tom Rini <trini-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
> Cc: Frank Rowand <frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

Good catch.

Applied, thanks.

> ---
> For background, the new alignment check triggered a crash in the 
> linux kernel. Yes, we should fix the error handling, but 
> fdt_check_header() shouldn't tell us the FDT is valid only to fail 
> later on.
> 
> Maybe we should move the check instead, but fdt_ro_probe_() and
> fdt_check_header() already have a lot of the same checks.
> 
>  libfdt/fdt.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/libfdt/fdt.c b/libfdt/fdt.c
> index 3e893073da05..9fe7cf4b747d 100644
> --- a/libfdt/fdt.c
> +++ b/libfdt/fdt.c
> @@ -90,6 +90,10 @@ int fdt_check_header(const void *fdt)
>  {
>  	size_t hdrsize;
>  
> +	/* The device tree must be at an 8-byte aligned address */
> +	if ((uintptr_t)fdt & 7)
> +		return -FDT_ERR_ALIGNMENT;
> +
>  	if (fdt_magic(fdt) != FDT_MAGIC)
>  		return -FDT_ERR_BADMAGIC;
>  	if (!can_assume(LATEST)) {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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