Re: [PATCH] loader/efi/fdt: Ensure FDT blob is 8-byte aligned

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Regards
Vladimir 'phcoder' Serbinenko

Le mer. 25 f=C3=A9vr. 2026, 16:48, <[email protected]> a =C3=A9crit :

> From: Mikhail Lappo <[email protected]>
>
> libfdt requires the FDT blob to be 8-byte aligned. The alignment is
> validated in fdt_check_header(), and misaligned blobs may be rejected
> or cause failures on architectures that enforce strict alignment.
>
> Currently the blob is allocated with grub_malloc(), which does not
> guarantee 8-byte alignment.

Actually it does. But I agree that explicit alignment is better. Or did you
experience malloc returning anything less than 16-byte aligned?
Reviewed-By: Vladimir Serbinenko<[email protected]>

> Replace it with grub_memalign(8, size)
> to ensure the required alignment.
>
> Signed-off-by: Mikhail Lappo <[email protected]>
> ---
>  grub-core/loader/efi/fdt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
> index e510b3491..f25d362d3 100644
> --- a/grub-core/loader/efi/fdt.c
> +++ b/grub-core/loader/efi/fdt.c
> @@ -38,6 +38,7 @@ static void *fdt;
>  #define FDT_ADDR_SIZE_EXTRA ((2 * grub_fdt_prop_entry_size
> (sizeof(grub_uint32_t))) + \
>                               sizeof (FDT_ADDR_CELLS_STRING) + \
>                               sizeof (FDT_SIZE_CELLS_STRING))
> +#define FDT_BLOB_ALIGNMENT 8
>
>  static const struct grub_arg_option options_fdtdump[] =3D {
>    {"prop",     'p', 0, N_("Get property."), N_("prop"), ARG_TYPE_STRING}=
,
> @@ -145,7 +146,7 @@ grub_cmd_devicetree (grub_command_t cmd __attribute__
> ((unused)),
>      goto out;
>
>    size =3D grub_file_size (dtb);
> -  blob =3D grub_malloc (size);
> +  blob =3D grub_memalign (FDT_BLOB_ALIGNMENT, size);
>    if (!blob)
>      goto out;
>
> --
> 2.44.0
>
>
> _______________________________________________
> Grub-devel mailing list
> [email protected]
> https://lists.gnu.org/mailman/listinfo/grub-devel
>

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<div dir=3D"auto"><div><div><br></div><div><br></div><div data-smartmail=3D=
"gmail_signature">Regards<br>Vladimir &#39;phcoder&#39; Serbinenko<br></div=
><br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" clas=
s=3D"gmail_attr">Le mer. 25 f=C3=A9vr. 2026, 16:48,  &lt;<a href=3D"mailto:=
[email protected]">[email protected]</a>&gt; a =C3=A9crit=C2=A0:<br><=
/div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-le=
ft:1px #ccc solid;padding-left:1ex">From: Mikhail Lappo &lt;<a href=3D"mail=
to:[email protected]" target=3D"_blank" rel=3D"noreferrer">miklelappo@gm=
ail.com</a>&gt;<br>
<br>
libfdt requires the FDT blob to be 8-byte aligned. The alignment is<br>
validated in fdt_check_header(), and misaligned blobs may be rejected<br>
or cause failures on architectures that enforce strict alignment.<br>
<br>
Currently the blob is allocated with grub_malloc(), which does not<br>
guarantee 8-byte alignment. </blockquote></div></div><div dir=3D"auto">Actu=
ally it does. But I agree that explicit alignment is better. Or did you exp=
erience malloc returning anything less than 16-byte aligned?</div><div dir=
=3D"auto">Reviewed-By: Vladimir Serbinenko&lt;<a href=3D"mailto:phcoder@gma=
il.com">[email protected]</a>&gt;</div><div dir=3D"auto"><div class=3D"gmai=
l_quote gmail_quote_container"><blockquote class=3D"gmail_quote" style=3D"m=
argin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Replace it wi=
th grub_memalign(8, size)<br>
to ensure the required alignment.<br>
<br>
Signed-off-by: Mikhail Lappo &lt;<a href=3D"mailto:[email protected]" ta=
rget=3D"_blank" rel=3D"noreferrer">[email protected]</a>&gt;<br>
---<br>
=C2=A0grub-core/loader/efi/fdt.c | 3 ++-<br>
=C2=A01 file changed, 2 insertions(+), 1 deletion(-)<br>
<br>
diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c<br>
index e510b3491..f25d362d3 100644<br>
--- a/grub-core/loader/efi/fdt.c<br>
+++ b/grub-core/loader/efi/fdt.c<br>
@@ -38,6 +38,7 @@ static void *fdt;<br>
=C2=A0#define FDT_ADDR_SIZE_EXTRA ((2 * grub_fdt_prop_entry_size (sizeof(gr=
ub_uint32_t))) + \<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 sizeof (FDT_ADDR_CELLS_STRING) + \<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 sizeof (FDT_SIZE_CELLS_STRING))<br>
+#define FDT_BLOB_ALIGNMENT 8<br>
<br>
=C2=A0static const struct grub_arg_option options_fdtdump[] =3D {<br>
=C2=A0 =C2=A0{&quot;prop&quot;,=C2=A0 =C2=A0 =C2=A0&#39;p&#39;, 0, N_(&quot=
;Get property.&quot;), N_(&quot;prop&quot;), ARG_TYPE_STRING},<br>
@@ -145,7 +146,7 @@ grub_cmd_devicetree (grub_command_t cmd __attribute__ (=
(unused)),<br>
=C2=A0 =C2=A0 =C2=A0goto out;<br>
<br>
=C2=A0 =C2=A0size =3D grub_file_size (dtb);<br>
-=C2=A0 blob =3D grub_malloc (size);<br>
+=C2=A0 blob =3D grub_memalign (FDT_BLOB_ALIGNMENT, size);<br>
=C2=A0 =C2=A0if (!blob)<br>
=C2=A0 =C2=A0 =C2=A0goto out;<br>
<br>
-- <br>
2.44.0<br>
<br>
<br>
_______________________________________________<br>
Grub-devel mailing list<br>
<a href=3D"mailto:[email protected]" target=3D"_blank" rel=3D"noreferrer">=
[email protected]</a><br>
<a href=3D"https://lists.gnu.org/mailman/listinfo/grub-devel" rel=3D"norefe=
rrer noreferrer" target=3D"_blank">https://lists.gnu.org/mailman/listinfo/g=
rub-devel</a><br>
</blockquote></div></div></div>

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