Re: [PATCH] efi: vars: commonize the 512-byte name buffer quirk

[Ard Biesheuvel]

Hello Jonggeun,


On Sat, 15 Aug 2026, at 09:48, Jonggeun Park wrote:
> Some old UEFI implementations reject GetNextVariableName() calls with
> a name buffer size larger than 512 bytes. Both efivar_init() and
> efi_pstore_read() open-code the same workaround of resetting the size
> to 512 on every iteration.
>
> Introduce efivar_get_next_variable_safe() which keeps this quirk in a
> single place, resolving the TODO in efi-pstore.c.
>
> No functional change intended.
>
> Signed-off-by: Jonggeun Park <jakejgpark@xxxxxxxxx>
> ---
>  drivers/firmware/efi/efi-pstore.c | 16 +++++-----------
>  drivers/firmware/efi/vars.c       | 21 +++++++++++++++++++++
>  fs/efivarfs/vars.c                |  4 +---
>  include/linux/efi.h               |  4 ++++
>  4 files changed, 31 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi-pstore.c 
> b/drivers/firmware/efi/efi-pstore.c
> index a5db3534f..a135d6e2f 100644
> --- a/drivers/firmware/efi/efi-pstore.c
> +++ b/drivers/firmware/efi/efi-pstore.c
> @@ -164,16 +164,6 @@ static ssize_t efi_pstore_read(struct 
> pstore_record *record)
>  	efi_status_t status;
> 
>  	for (;;) {
> -		/*
> -		 * A small set of old UEFI implementations reject sizes
> -		 * above a certain threshold, the lowest seen in the wild
> -		 * is 512.
> -		 *
> -		 * TODO: Commonize with the iteration implementation in
> -		 *       fs/efivarfs to keep all the quirks in one place.
> -		 */
> -		varname_size = 512;
> -
>  		/*
>  		 * If this is the first read() call in the pstore enumeration,
>  		 * varname will be the empty string, and the GetNextVariable()
> @@ -185,8 +175,12 @@ static ssize_t efi_pstore_read(struct 
> pstore_record *record)
>  		 * store varname in record->psi->data. Given that we only
>  		 * enumerate variables with the efi-pstore GUID, there is no
>  		 * need to record the guid return value.
> +		 *
> +		 * The 512-byte name buffer quirk is handled inside
> +		 * efivar_get_next_variable_safe().
>  		 */
> -		status = efivar_get_next_variable(&varname_size, varname, &guid);
> +		status = efivar_get_next_variable_safe(&varname_size, varname,
> +						       &guid);
>  		if (status == EFI_NOT_FOUND)
>  			return 0;
> 
> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index 3700e9869..8e69f3632 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -265,3 +265,24 @@ efi_status_t efivar_query_variable_info(u32 attr,
>  			remaining_space, max_variable_size);
>  }
>  EXPORT_SYMBOL_NS_GPL(efivar_query_variable_info, "EFIVAR");
> +
> +/*
> + * efivar_get_next_variable_safe() - enumerate the next name/vendor 
> pair
> + *
> + * Wrapper around efivar_get_next_variable() that keeps the 512-byte 
> name
> + * buffer quirk in one place. Some old UEFI implementations reject 
> name buffer
> + * sizes larger than 512 bytes (the lowest seen in the wild), so this 
> always
> + * requests 512 bytes; callers must provide a buffer of at least that 
> size.
> + *
> + * Must be called with efivars_lock held.
> + */
> +efi_status_t efivar_get_next_variable_safe(unsigned long *name_size,
> +					   efi_char16_t *name,
> +					   efi_guid_t *vendor)
> +{
> +	BUILD_BUG_ON(EFI_VAR_NAME_LEN < 512);
> +	*name_size = 512;
> +
> +	return efivar_get_next_variable(name_size, name, vendor);
> +}
> +EXPORT_SYMBOL_NS_GPL(efivar_get_next_variable_safe, "EFIVAR");

Don't add a new function here - just move the logic into the existing
efivar_get_next_variable(), which has only two callers.