linux-kernel - Re: [PATCH] arm64/cpufeature: Validate feature bits spacing in arm64_ftr

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Message-ID: <9c2a5410-044e-03cb-9233-900389d0dfea@arm.com>
Date:   Tue, 30 Jun 2020 11:16:18 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     anshuman.khandual@....com, linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, will@...nel.org, broonie@...nel.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/cpufeature: Validate feature bits spacing in
 arm64_ftr_regs[]

On 06/30/2020 02:49 AM, Anshuman Khandual wrote:
> 
> 
> On 06/29/2020 04:12 PM, Suzuki K Poulose wrote:
>> On 06/16/2020 03:25 AM, Anshuman Khandual wrote:
>>> arm64_feature_bits for a register in arm64_ftr_regs[] are in a descending
>>> order as per their shift values. Validate that these features bits are
>>> defined correctly and do not overlap with each other. This check protects
>>> against any inadvertent erroneous changes to the register definitions.
>>>
>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>> Cc: Will Deacon <will@...nel.org>
>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>> Cc: Mark Brown <broonie@...nel.org>
>>> Cc: Mark Rutland <mark.rutland@....com>
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>>> ---
>>> Applies on 5.8-rc1.
>>>
>>>    arch/arm64/kernel/cpufeature.c | 45 +++++++++++++++++++++++++++++++---
>>>    1 file changed, 42 insertions(+), 3 deletions(-)

>>> +        }
>>>    -    /* Check that the array is sorted so that we can do the binary search */
>>> -    for (i = 1; i < ARRAY_SIZE(arm64_ftr_regs); i++)
>>> +        /*
>>> +         * Skip the first register. There is nothing to
>>> +         * compare against for now.
>>> +         */
>>> +        if (i == 0)
>>> +            continue;
>>
>> You are starting at 1 already, so you may skip this check.
> 
> Actually, now we are starting with 0 instead for both i and j.
> Hence this check would be required.

Sorry, ignore that.

Suzuki