linux-kernel - Re: [PATCH 03/10] efi/libstub: use a helper to iterate over a EFI handle array

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Date:   Sat, 14 Dec 2019 15:32:57 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH 03/10] efi/libstub: use a helper to iterate over a EFI
 handle array

On Sat, Dec 14, 2019 at 06:57:28PM +0100, Ard Biesheuvel wrote:
> Iterating over a EFI handle array is a bit finicky, since we have
> to take mixed mode into account, where handles are only 32-bit
> while the native efi_handle_t type is 64-bit.
> 
> So introduce a helper, and replace the various occurrences of
> this pattern.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  
> +#define for_each_efi_handle(handle, array, size, i)			\
> +	for (i = 1, handle = efi_is_64bit()				\
> +		? (efi_handle_t)(unsigned long)((u64 *)(array))[0]	\
> +		: (efi_handle_t)(unsigned long)((u32 *)(array))[0];	\
> +	    i++ <= (size) / (efi_is_64bit() ? sizeof(efi_handle_t)	\
> +					     : sizeof(u32));		\
> +	    handle = efi_is_64bit()					\
> +		? (efi_handle_t)(unsigned long)((u64 *)(array))[i]	\
> +		: (efi_handle_t)(unsigned long)((u32 *)(array))[i])
> +
>  /*
>   * The UEFI spec and EDK2 reference implementation both define EFI_GUID as
>   * struct { u32 a; u16; b; u16 c; u8 d[8]; }; and so the implied alignment
> -- 
> 2.17.1
> 

This would access one past the array, no? Eg if the array has one
handle, i is incremented to 2 the first time the condition is checked,
then the loop increment will access array[2] before the condition is
checked again. There seem to be at least a couple of other for_each
macros that might have similar issues.

How about the below instead?

#define for_each_efi_handle(handle, array, size, i)			\
	for (i = 0;							\
	    (i < (size) / (efi_is_64bit() ? sizeof(efi_handle_t)	\
					  : sizeof(u32))) &&		\
	    ((handle = efi_is_64bit()					\
		? ((efi_handle_t *)(array))[i]				\
		: (efi_handle_t)(unsigned long)((u32 *)(array))[i]), 1);\
	    i++)