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Subject: Re: [PATCH 1/3] MIPS: KASLR: Correcte valid bits in
 apply_r_mips_26_rel
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
References: <1605752954-10368-1-git-send-email-hejinyang@loongson.cn>
 <20201119123636.GA4936@alpha.franken.de>
Cc:     Huacai Chen <chenhc@lemote.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <0fbbdce0-1449-fb40-0a11-2cded0c3472b@loongson.cn>
Date:   Fri, 20 Nov 2020 10:48:07 +0800
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Hi,

On 11/19/2020 08:36 PM, Thomas Bogendoerfer wrote:
> On Thu, Nov 19, 2020 at 10:29:12AM +0800, Jinyang He wrote:
>> Apply_r_mips_26_rel() relocates instructions like j, jal and etc. These
>> instructions consist of 6bits function field and 26bits address field.
>> The value of target_addr as follows,
>> =================================================================
>> |     high 4bits           |            low 28bits              |
>> =================================================================
>> |the high 4bits of this PC | the low 26bits of instructions << 2|
>> =================================================================
>> Thus, loc_orig and log_new both need high 4bits ranther than high 6bits.
> 						  rather
>
>> Replace 0x3ffffff with 0xfffffff.
>>
>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>> ---
>>   arch/mips/kernel/relocate.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
>> index 3d80a51..709cfa0 100644
>> --- a/arch/mips/kernel/relocate.c
>> +++ b/arch/mips/kernel/relocate.c
>> @@ -95,7 +95,7 @@ static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
>>   
>>   	/* Original target address */
>>   	target_addr <<= 2;
>> -	target_addr += (unsigned long)loc_orig & ~0x03ffffff;
>> +	target_addr += (unsigned long)loc_orig & ~0x0fffffff;
> how about using
>
> 	target_addr += (unsigned long)log_orig & 0xf0000000;
>
> which makes it IMHO even clearer what this does ?
That sounds good. I'll send v2 later.

Thanks,
Jinyang.

> Thomas.
>