Re: riscv+KASAN does not boot

[Alex Ghiti]

Le 3/9/21 à 12:11 PM, Dmitry Vyukov a écrit :
> On Fri, Feb 19, 2021 at 11:26 PM 'Palmer Dabbelt' via syzkaller
> <syzkaller@xxxxxxxxxxxxxxxx> wrote:
> > On Fri, 19 Feb 2021 10:53:43 PST (-0800), dvyukov@xxxxxxxxxx wrote:
> > > On Fri, Feb 19, 2021 at 6:01 PM Alex Ghiti <alex@xxxxxxxx> wrote:
> > > > Hi Dmitry,
> > > >
> > > > Le 2/18/21 à 6:36 AM, Dmitry Vyukov a écrit :
> > > > > On Thu, Feb 18, 2021 at 8:54 AM Alex Ghiti <alex@xxxxxxxx> wrote:
> > > > > > Hi Dmitry,
> > > > > >
> > > > > > > On Wed, Feb 17, 2021 at 5:36 PM Alex Ghiti <alex@xxxxxxxx> wrote:
> > > > > > > > Le 2/16/21 à 11:42 PM, Dmitry Vyukov a écrit :
> > > > > > > > > On Tue, Feb 16, 2021 at 9:42 PM Alex Ghiti <alex@xxxxxxxx> wrote:
> > > > > > > > > > Hi Dmitry,
> > > > > > > > > >
> > > > > > > > > > Le 2/16/21 à 6:25 AM, Dmitry Vyukov a écrit :
> > > > > > > > > > > On Tue, Feb 16, 2021 at 12:17 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> > > > > > > > > > > > On Fri, Jan 29, 2021 at 9:11 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> 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
> > > > > > > > > >
> > > > > > > > > > What's weird is that I don't have any issue without this patch with the
> > > > > > > > > > following config whereas it indeed seems required for KASAN. But when
> > > > > > > > > > looking at the segfaults you got earlier, the segfault address is 0xbb0
> > > > > > > > > > and the cause is an instruction page fault: this address is the PLT base
> > > > > > > > > > address in vdso.so and an instruction page fault would mean that someone
> > > > > > > > > > tried to jump at this address, which is weird. At first sight, that does
> > > > > > > > > > not seem related to your patch above, but clearly I may be wrong.
> > > > > > > > > >
> > > > > > > > > > Tobias, did you observe the same segfaults as Dmitry ?
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > I noticed that not all buildroot images use VDSO, it seems to be
> > > > > > > > > dependent on libc settings (at least I think I changed it in the
> > > > > > > > > past).
> > > > > > > >
> > > > > > > > Ok, I used uClibc but then when using glibc, I have the same segfaults,
> > > > > > > > only when KASAN is enabled. And your patch fixes the problem. I will try
> > > > > > > > to take a look later to better understand the problem.
> > > > > > > >
> > > > > > > > > I also booted an image completely successfully including dhcpd/sshd
> > > > > > > > > start, but then my executable crashed in clock_gettime. The executable
> > > > > > > > > was build on linux/amd64 host with "riscv64-linux-gnu-gcc -static"
> > > > > > > > > (10.2.1).
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > > > Second issue I am seeing seems to be related to text segment size.
> > > > > > > > > > > I check out v5.11 and use this config:
> > > > > > > > > > > https://gist.github.com/dvyukov/6af25474d455437577a84213b0cc9178
> > > > > > > > > >
> > > > > > > > > > This config gave my laptop a hard time ! Finally I was able to boot
> > > > > > > > > > correctly to userspace, but I realized I used my sv48 branch...Either I
> > > > > > > > > > fixed your issue along the way or I can't reproduce it, I'll give it a
> > > > > > > > > > try tomorrow.
> > > > > > > > >
> > > > > > > > > Where is your branch? I could also test in my setup on your branch.
> > > > > > > >
> > > > > > > > You can find my branch int/alex/riscv_kernel_end_of_address_space_v2
> > > > > > > > here: https://github.com/AlexGhiti/riscv-linux.git
> > > > > > >
> > > > > > > No, it does not work for me.
> > > > > > >
> > > > > > > Source is on b61ab6c98de021398cd7734ea5fc3655e51e70f2 (HEAD,
> > > > > > > int/alex/riscv_kernel_end_of_address_space_v2)
> > > > > > > Config is https://gist.githubusercontent.com/dvyukov/6af25474d455437577a84213b0cc9178/raw/55b116522c14a8a98a7626d76df740d54f648ce5/gistfile1.txt
> > > > > > >
> > > > > > > riscv64-linux-gnu-gcc -v
> > > > > > > gcc version 10.2.1 20210110 (Debian 10.2.1-6+build1)
> > > > > > >
> > > > > > > qemu-system-riscv64 --version
> > > > > > > QEMU emulator version 5.2.0 (Debian 1:5.2+dfsg-3)
> > > > > > >
> > > > > > > qemu-system-riscv64 \
> > > > > > > -machine virt -smp 2 -m 2G \
> > > > > > > -device virtio-blk-device,drive=hd0 \
> > > > > > > -drive file=image-riscv64,if=none,format=raw,id=hd0 \
> > > > > > > -kernel arch/riscv/boot/Image \
> > > > > > > -nographic \
> > > > > > > -device virtio-rng-device,rng=rng0 -object
> > > > > > > rng-random,filename=/dev/urandom,id=rng0 \
> > > > > > > -netdev user,id=net0,host=10.0.2.10,hostfwd=tcp::10022-:22 -device
> > > > > > > virtio-net-device,netdev=net0 \
> > > > > > > -append "root=/dev/vda earlyprintk=serial console=ttyS0 oops=panic
> > > > > > > panic_on_warn=1 panic=86400 earlycon"
> > > > > >
> > > > > > It still works for me but I had to disable CONFIG_DEBUG_INFO_BTF (I
> > > > > > don't think that changes anything at runtime). But your above command
> > > > > > line does not work for me as it appears you do not load any firmware, if
> > > > > > I add -bios images/fw_jump.elf, it works. But then I don't know where
> > > > > > your opensbi output below comes from...
> > > > > >
> > > > > > And regarding your issue with calling clock_gettime 'directly' compared
> > > > > > to using the syscall, I have the same consistent output from both calls.
> > > > > >
> > > > > > I have an older gcc (9.3.0) and the same qemu. I think what is missing
> > > > > > here is your buildroot config, so that we have the exact same
> > > > > > environment: could you post your buildroot config as well ?
> > > > >
> > > > > I don't think the image is relevant because I don't even get to kernel
> > > > > code. If the kernel will complain about no init later, that's fine.
> > > > > Re bios, this version of qemu already has OpenSBI bios builtin, you
> > > > > can pass -bios default, but that's, well, the default :)
> > > > > Here are more reproducible repro instructions that capture gcc and
> > > > > qemu. I think gcc version may be potentially relevant as I suspect
> > > > > code size.
> > > > >
> > > > >
> > > > > curl https://gist.githubusercontent.com/dvyukov/6af25474d455437577a84213b0cc9178/raw/55b116522c14a8a98a7626d76df740d54f648ce5/gistfile1.txt
> > > > > > $KERNEL_SRC/.config
> > > > > docker pull gcr.io/syzkaller/syzbot
> > > > > docker run -it -v $KERNEL_SRC:/kernel gcr.io/syzkaller/syzbot
> > > > > cd /kernel
> > > > > make -j72 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- olddefconfig
> > > > > make -j72 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
> > > > > qemu-system-riscv64 -machine virt -smp 2 -m 4G -kernel
> > > > > arch/riscv/boot/Image -nographic -append "earlycon earlyprintk=serial
> > > > > console=ttyS0"
> > > > > [this does not, only OpenSBI output]
> > > >
> > > > Indeed the issue was code size, please find the fix below. I will send a
> > > > proper patch once I made sure the fix is the right one, but I'm pretty
> > > > confident, there's no reason to limit the mapping size to 128MB whereas
> > > > we have a whole pgdir.
> > >
> > > Great you get to the bottom of this!
> > > Riscv kernels are going to be YUGE!
> >
> > IIRC I tried that a while ago and it didn't work.  It's possible I was just
> > running into some other bug, but I'm just build testing allyesconfig as opposed
> > to boot testing it.
> >
> > If you've got a setup that does boot I'm happy to take a patch, though.  It'll
> > at least be one step forward.
>
>
>
> OK, it's getting better.

Nice :)

> The next issue is called "512 bytes should be enough for everyone!" :)
> https://elixir.bootlin.com/linux/v5.12-rc2/source/include/uapi/asm-generic/setup.h#L5
> Most other arches redefine it to something bigger:
> https://elixir.bootlin.com/linux/v5.12-rc2/source/arch/s390/include/uapi/asm/setup.h#L10
> even arm32 redefines it.
> I am not sure the default is even reasonable anymore. 

Some archs override this value to 256, but git blame shows this is 
(very) old. I agree that 512 as default seems low.

> Failure mode is
> also not nice (silent truncation).

Agreed, maybe we could still have the default value and checks the 
terminating null character is somewhere and bugs if not, I'll take a look.

> We are trying to pass this:
>
> earlyprintk=serial oops=panic nmi_watchdog=panic panic=86400
> net.ifnames=0 sysctl.kernel.hung_task_all_cpu_backtrace=1
> ima_policy=tcb kvm-intel.nested=1 nf-conntrack-ftp.ports=20000
> nf-conntrack-tftp.ports=20000 nf-conntrack-sip.ports=20000
> nf-conntrack-irc.ports=20000 nf-conntrack-sane.ports=20000
> vivid.n_devs=16 vivid.multiplanar=1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2
> netrom.nr_ndevs=16 rose.rose_ndevs=16 spec_store_bypass_disable=prctl
> numa=fake=2 nopcid dummy_hcd.num=8 binder.debug_mask=0
> rcupdate.rcu_expedited=1 watchdog_thresh=165
> workqueue.watchdog_thresh=420 panic_on_warn=1
>
> The last part gets truncated and we are getting false workqueue watchdog stalls.
>
> Could you please increase it?

I will propose a patchset that increases the default value and cleans 
archs up accordingly too.

Thanks again,

Alex

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