linux-kernel - Re: [PATCH v2] x86/microcode/AMD: check microcode file sanity before loading it

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Date:   Mon, 12 Mar 2018 14:06:53 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/microcode/AMD: check microcode file sanity before
 loading it

On Mon, Mar 12, 2018 at 01:56:59PM +0100, Maciej S. Szmigiero wrote:
> The equivalent CPU table is allocated using vmalloc() so it is nice
> when the maximum size is an integer multiple of the page size.

Arbitrary.

> Since the maximum entry count in current microcode files is 18 the

Where did you dream up that 18?

> maximum size of 256 entries (or one page) gives us plenty of headroom.

Arbitrary.

> Also, looking in the past, there probably won't be more than 256 AMD CPU
> types in one CPU family.

Wrong.

The only limitation on the equivalence table size we have is the 32-bit
unsigned length field at offset 8 in the equivalence table header.

> This limit is an absolute upper cap of a patch size.

More dreamt up crap.

See verify_patch_size() for the actual patch sizes.

-- 
Regards/Gruss,
    Boris.

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