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

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Date:   Fri, 11 Nov 2022 13:29:13 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
CC:     Borislav Petkov <bp@...en8.de>,
        Jithu Joseph <jithu.joseph@...el.com>, <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>, <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>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v2 10/14] platform/x86/intel/ifs: Add metadata validation

On Fri, Nov 11, 2022 at 10:48:49AM -0800, Dave Hansen wrote:
> 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?

Maybe should we do a cleanup patch to move struct microcode_header_intel
also to u32 format then add meta_data to follow the same style?

When we defined struct meta_data followed the format and style that was
already in place.

The suggestion below is a lot nicer, let the compiler do te job.

> 
> 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.