linux-kernel - Re: [syzbot] kernel panic: corrupted stack end in rtnl

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Message-ID: <CACT4Y+ae7WRhnmiTuFg6zrL7z_8rUrmWzopOGMZv6f0ONmd3yg@mail.gmail.com>
Date:   Mon, 14 Mar 2022 13:05:07 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     syzbot <syzbot+0600986d88e2d4d7ebb8@...kaller.appspotmail.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [syzbot] kernel panic: corrupted stack end in rtnl_newlink

On Mon, 14 Mar 2022 at 11:44, David Laight <David.Laight@...lab.com> wrote:
>
> From: Dmitry Vyukov
> > Sent: 14 March 2022 09:09
> >
> > On Mon, 14 Mar 2022 at 09:22, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > >
> > > On Mon, 14 Mar 2022 at 09:17, syzbot
> > > <syzbot+0600986d88e2d4d7ebb8@...kaller.appspotmail.com> wrote:
> > > >
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    0966d385830d riscv: Fix auipc+jalr relocation range checks
> > > > git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17fe80c5700000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=6295d67591064921
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=0600986d88e2d4d7ebb8
> > > > compiler:       riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for
> > Debian) 2.35.2
> > > > userspace arch: riscv64
> > >
> > > +linux-riscv
> > >
> > > Riscv needs to increase stack size under KASAN.
> > > I will send a patch.
>
> With vmalloc()ed stacks is it possible to allocate an extra page
> of KVA that isn't backed by memory as a 'guard page' so that
> stack overflow faults immediately?
>
> Probably worth enforcing for KASAN builds where the compilers
> have a nasty habit of using lot more stack space that might
> be expected.

Yes, this would be useful. At least for x86 we use and rely on this.