linux-kernel - Re: [PATCH rdma-next 1/4] gcov: Open-code kmemdup() to work correctly with kernel and user space pointers

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Message-ID: <20200902174600.GK59010@unreal>
Date:   Wed, 2 Sep 2020 20:46:00 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Colin Ian King <colin.king@...onical.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH rdma-next 1/4] gcov: Open-code kmemdup() to work
 correctly with kernel and user space pointers

On Wed, Sep 02, 2020 at 10:38:20AM -0700, Linus Torvalds wrote:
> On Wed, Sep 2, 2020 at 1:55 AM Leon Romanovsky <leon@...nel.org> wrote:
> >
> > The kernel with KASAN and GCOV enabled generates the following splat
> > due to the situation that gcov_info can be both user and kernel pointer.
>
> I can't parse the above explanation..
>
> > It is triggered by the memcpy() inside kmemdup(), so as a possible solution
> > let's copy fields manually.
>
> .. and I don't see why copying the fields manually makes a difference.
>
> Can you explain more?

Definitely my explanation is wrong, but it was my interpretation of
"BUG: KASAN: global-out-of-bounds in kmemdup+0x43/0x70" line. I saw
that the failure was in memcpy() inside of kmemdup(), so I changed
from memcpy to be copy_from_user() and it solved the KASAN warning.

This is why I wrote "both user and kernel pointer".

Thanks

>
>              Linus