linux-kernel - Re: [PATCH v3 3/9] x86/microcode/AMD: install_equiv_cpu

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Date:   Thu, 15 Mar 2018 00:46:05 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/9] x86/microcode/AMD: install_equiv_cpu_table()
 should not return (signed) int

On 14.03.2018 18:58, Borislav Petkov wrote:
> On Tue, Mar 13, 2018 at 10:06:34PM +0100, Maciej S. Szmigiero wrote:
>> The maximum possible value returned by install_equiv_cpu_table() is
>> UINT_MAX + CONTAINER_HDR_SZ (on a 64-bit kernel).
>> This is more than (signed) int type currently returned by this function can
>> hold so this function will need to return a size_t instead.
> 
> I'm trying to parse this but I'm not really sure.
> 
> All I know is:
> 
> 	unsigned int size = ibuf[2];
> 
> and that is really a 4-byte unsigned quantity so anything less is an
> arbitrary limitation.

There is no limit on CPU equivalence table length in this patch series
like it was in the previous version.

The maximum possible value returned by install_equiv_cpu_table() of
UINT_MAX + CONTAINER_HDR_SZ comes from the maximum value of this 'size'
variable (that is UINT_MAX) plus the header length of CONTAINER_HDR_SZ.
This won't fit in 'int' type, hence this patch.

That's because this functions tells its caller how much bytes to skip
from the beginning of a microcode container file to the first patch
section contained in it.

Maciej