linux-kernel - Re: [PATCH] kmemleak: fix kmemleak false positive report with HW tag-based kasan enable

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Message-Id: <20211119144359.b70d2fde7631bd14cd9652e3@linux-foundation.org>
Date:   Fri, 19 Nov 2021 14:43:59 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Nicholas Tang (鄭秦輝) 
        <nicholas.tang@...iatek.com>,
        James Hsu ( 徐慶薰) 
        <James.Hsu@...iatek.com>,
        Yee Lee (李建誼) 
        <Yee.Lee@...iatek.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        <kuan-ying.lee@...iatek.com>
Subject: Re: [PATCH] kmemleak: fix kmemleak false positive report with HW
 tag-based kasan enable

On Fri, 19 Nov 2021 23:12:55 +0800 Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com> wrote:

> > > > Call sequence:
> > > > ptr = kmalloc(size, GFP_KERNEL);
> > > > page = virt_to_page(ptr);
> > > > kfree(page_address(page));
> > > > ptr = kmalloc(size, GFP_KERNEL);
> > 
> > How is this call sequence valid? page_address returns the address of
> > the start of the page, while kmalloced object could have been located
> > in the middle of it.
> 
> Thanks for pointing out. I miss the offset.
> 
> It should be listed as below.
> 
> ptr = kmalloc(size, GFP_KERNEL);
> page = virt_to_page(ptr);
> offset = offset_in_page(ptr);
> kfree(page_address(page) + offset);
> ptr = kmalloc(size, GFP_KERNEL);

I updated the changelog to reflect this.