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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 11 Nov 2022 12:30:26 -0800
From:   "Joseph, Jithu" <jithu.joseph@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...en8.de>
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 11/11/2022 10:48 AM, 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?

The struct was mirroring the initial 256 bytes of the metadata section of IFS test image (replicated below). 
I will change it to union with a separate padding member as Dave suggests below.

    IFS Metadata layout
   +----------------------+  0
   |META_TYPE_IFS (=1)    |
   +----------------------+
   |meta_size             |
   +----------------------+
   |test type             |
   +----------------------+
   |fusa info             |
   +----------------------+
   |total images          |
   +----------------------+
   |current image#        |
   +----------------------+
   |total chunks          |
   +----------------------+
   |starting chunk        |
   +----------------------+
   |size per chunk        |
   +----------------------+
   |chunks per stride     |
   +----------------------+
   |Reserved[54]          |
   +----------------------+ 256
   |                      |
   |                      |
   |                      |
   |                      |
   |Test Data/Chunks      |
   |                      |
   |                      |
   |                      |
   |                      |
   +----------------------+  meta_size
   |   META_TYPE_END (=0) |
   +----------------------+  meta_size + 4
   |   size of end (=8)   |
   |                      |
   +----------------------+  meta_size + 8



> 
> ... 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.

Thanks, will adopt this.

Jithu