linux-kernel - Re: [PATCH v2 10/14] platform/x86/intel/ifs: Add metadata validation

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Date:   Fri, 11 Nov 2022 10:48:49 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Jithu Joseph <jithu.joseph@...el.com>
Cc:     hdegoede@...hat.com, markgross@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, gregkh@...uxfoundation.org, ashok.raj@...el.com,
        tony.luck@...el.com, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, patches@...ts.linux.dev,
        ravi.v.shankar@...el.com, thiago.macieira@...el.com,
        athenas.jimenez.gonzalez@...el.com, sohil.mehta@...el.com
Subject: Re: [PATCH v2 10/14] platform/x86/intel/ifs: Add metadata validation

On 11/11/22 10:39, Borislav Petkov wrote:
>> +struct meta_data {
>> +	unsigned int meta_type;		// metadata type
>> +	unsigned int meta_size;		// size of this entire struct including hdrs.
>> +	unsigned int test_type;		// IFS test type
>> +	unsigned int fusa_info;		// Fusa info
>> +	unsigned int total_images;	// Total number of images
>> +	unsigned int current_image;	// Current Image #
>> +	unsigned int total_chunks;	// Total number of chunks in this image
>> +	unsigned int starting_chunk;	// Starting chunk number in this image
>> +	unsigned int size_per_chunk;	// size of each chunk
>> +	unsigned int chunks_per_stride;	// number of chunks in a stride
>> +	unsigned int reserved[54];	// Align to 256 bytes for chunk alignment.
> That looks weird.
> 
> __packed and __aligned doesn't work?

... and don't we try to use fixed-size typed in hardware structures,
like u32?

There are also much nicer ways to do this:

union meta_data {
	struct {
		u32 meta_type;		// metadata type
		u32 meta_size;		// size of ...
	};
	u8 padding[IFS_CHUNK_ALIGNMENT];
}

That doesn't have any magic linkage between the magic "54" (times 4) and
IFS_CHUNK_ALIGNMENT.  It makes the compiler do the hard work for you.

Voila, you have a union that's always IFS_CHUNK_ALIGNMENT in size,  No
magic 54's necessary.