On 2024-05-22 23:02:17+0000, Jiaxun Yang wrote:
> fdt_check_header(__dtb_start) will always success because kernel
> provided a dummy dtb, and by coincidence __dtb_start clashed with
> entry of this dummy dtb. The consequence is fdt passed from
> firmware will never be taken.
>
> Fix by trying to utilise __dtb_start only when CONFIG_BUILTIN_DTB
> is enabled.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 7b937cc243e5 ("of: Create of_root if no dtb provided by firmware")
> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> ---
> v3: Better reasoning in commit message, thanks Binbin and Huacai!
> ---
> arch/loongarch/kernel/setup.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 60e0fe97f61a..ea6d5db6c878 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -275,16 +275,18 @@ static void __init arch_reserve_crashkernel(void)
> static void __init fdt_setup(void)
> {
> #ifdef CONFIG_OF_EARLY_FLATTREE
> - void *fdt_pointer;
> + void *fdt_pointer = NULL;
>
> /* ACPI-based systems do not require parsing fdt */
> if (acpi_os_get_root_pointer())
> return;
>
> +#ifdef CONFIG_BUILTIN_DTB
> /* Prefer to use built-in dtb, checking its legality first. */
> if (!fdt_check_header(__dtb_start))
> fdt_pointer = __dtb_start;
> - else
> +#endif
> + if (!fdt_pointer)
> fdt_pointer = efi_fdt_pointer(); /* Fallback to firmware dtb */
Prefer to use non-ifdef logic:
if (IS_ENABLED(CONFIG_BUILTIN_DTB) && !fdt_check_header(__dtb_start))
fdt_pointer = __dtb_start;
This is shorter, easier to read and will prevent bitrot.
The code will be typechecked but then optimized away, so no
runtime overhead exists.
>
> if (!fdt_pointer || fdt_check_header(fdt_pointer))
>
> --
> 2.43.0
>
