linux-kernel - Re: [PATCH 1/6] efi: Retrieve Apple device properties

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Message-ID: <20160804151345.GM3636@codeblueprint.co.uk>
Date:	Thu, 4 Aug 2016 16:13:45 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Lukas Wunner <lukas@...ner.de>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andreas Noever <andreas.noever@...il.com>,
	Pierre Moreau <pierre.morrow@...e.fr>, reverser@....as,
	grub-devel@....org, x86@...nel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/6] efi: Retrieve Apple device properties

On Thu, 28 Jul, at 02:25:41AM, Lukas Wunner wrote:
> 
> diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> index ff574da..7262ee4 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -571,6 +571,55 @@ free_handle:
>  	efi_call_early(free_pool, pci_handle);
>  }
>  
> +static void retrieve_apple_device_properties(struct boot_params *params)
> +{
> +	efi_guid_t guid = APPLE_PROPERTIES_PROTOCOL_GUID;
> +	struct setup_data *data, *new;
> +	efi_status_t status;
> +	void *properties;
> +	u32 size = 0;
> +
> +	status = efi_early->call(
> +			(unsigned long)sys_table->boottime->locate_protocol,
> +			&guid, NULL, &properties);
> +	if (status != EFI_SUCCESS)
> +		return;
> +
> +	do {
> +		status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
> +			size + sizeof(struct setup_data), &new);
> +		if (status != EFI_SUCCESS) {
> +			efi_printk(sys_table,
> +				   "Failed to alloc mem for properties\n");
> +			return;
> +		}
> +		status = efi_early->call(efi_early->is64 ?
> +			((apple_properties_protocol_64 *)properties)->get_all :
> +			((apple_properties_protocol_32 *)properties)->get_all,
> +			properties, new->data, &size);
> +		if (status == EFI_BUFFER_TOO_SMALL)
> +			efi_call_early(free_pool, new);
> +	} while (status == EFI_BUFFER_TOO_SMALL);

Is this looping really required? Do we not know ahead of time what we
expect the size to be? Writing this as a potentially infinite loop (if
broken firmware always returns EFI_BUFFER_TOO_SMALL) is a bad idea.