linux-kernel - Re: fsl_ifc_nand: are blank pages protected by ECC?

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]

Message-ID: <20170420141553.1012a79a@bbrezillon>
Date:   Thu, 20 Apr 2017 14:15:53 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Pavel Machek <pavel@....cz>
Cc:     richard@....at, dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, cyrille.pitchen@...el.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mark.marshall@...cronenergy.com, b44839@...escale.com,
        prabhakar@...escale.com
Subject: Re: fsl_ifc_nand: are blank pages protected by ECC?

On Thu, 20 Apr 2017 13:40:57 +0200
Pavel Machek <pavel@....cz> wrote:

> Hi!
> 
> > > Would it make sense to only do hweight if *bitmap != ~0ULL ? Would it
> > > make sense to only check for bitflips > bitflips_threshold each 128
> > > bytes or something like that?  
> > 
> > I didn't go as far as you did and simply assumed hweight32/64() were
> > already optimized. Feel free to propose extra improvements.  
> 
> I'd propose this one (only compile tested, sorry, not sure how to test
> this one). If we see ~0UL, there's no need for hweight, and no need to
> check number of bitflips. So this should be net win.

Looks good to me. Can you send a patch with a real commit message?

Thanks,

Boris

> 
> Signed-off-by: Pavel Machek <pavel@...x.de>
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index b0524f8..96c27ec 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -1357,7 +1357,10 @@ static int nand_check_erased_buf(void *buf, int len, int bitflips_threshold)
>  
>  	for (; len >= sizeof(long);
>  	     len -= sizeof(long), bitmap += sizeof(long)) {
> -		weight = hweight_long(*((unsigned long *)bitmap));
> +		unsigned long d = *((unsigned long *)bitmap);
> +		if (d == ~0UL)
> +			continue;
> +		weight = hweight_long(d);
>  		bitflips += BITS_PER_LONG - weight;
>  		if (unlikely(bitflips > bitflips_threshold))
>  			return -EBADMSG;
>