linux-kernel - Re: riscv+KASAN does not boot

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Message-ID: <CACT4Y+ZNJBnkKHXUf=tm_yuowvZvHwN=0rmJ=7J+xFd+9r_6pQ@mail.gmail.com>
Date:   Tue, 16 Feb 2021 12:17:30 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Alex Ghiti <alex@...ti.fr>
Cc:     Tobias Klauser <tklauser@...tanz.ch>,
        Albert Ou <aou@...s.berkeley.edu>,
        Bjorn Topel <bjorn.topel@...il.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, nylon7@...estech.com,
        syzkaller <syzkaller@...glegroups.com>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: riscv+KASAN does not boot

On Fri, Jan 29, 2021 at 9:11 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > I was fixing KASAN support for my sv48 patchset so I took a look at your
> > issue: I built a kernel on top of the branch riscv/fixes using
> > https://github.com/google/syzkaller/blob/269d24e857a757d09a898086a2fa6fa5d827c3e1/dashboard/config/linux/upstream-riscv64-kasan.config
> > and Buildroot 2020.11. I have the warnings regarding the use of
> > __virt_to_phys on wrong addresses (but that's normal since this function
> > is used in virt_addr_valid) but not the segfaults you describe.
>
> Hi Alex,
>
> Let me try to rebuild buildroot image. Maybe there was something wrong
> with my build, though, I did 'make clean' before doing. But at the
> same time it worked back in June...
>
> Re WARNINGs, they indicate kernel bugs. I am working on setting up a
> syzbot instance on riscv. If there a WARNING during boot then the
> kernel will be marked as broken. No further testing will happen.
> Is it a mis-use of WARN_ON? If so, could anybody please remove it or
> replace it with pr_err.


Hi,

I've localized one issue with riscv/KASAN:
KASAN breaks VDSO and that's I think the root cause of weird faults I
saw earlier. The following patch fixes it.
Could somebody please upstream this fix? I don't know how to add/run
tests for this.
Thanks

diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 0cfd6da784f84..cf3a383c1799d 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -35,6 +35,7 @@ CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
 # Disable gcov profiling for VDSO code
 GCOV_PROFILE := n
 KCOV_INSTRUMENT := n
+KASAN_SANITIZE := n

 # Force dependency
 $(obj)/vdso.o: $(obj)/vdso.so