Re: riscv+KASAN does not boot

Dmitry Vyukov
2021-02-19T18:55:02Z

On Fri, Feb 19, 2021 at 6:01 PM Alex Ghiti <alex@ghiti.fr> 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@ghiti.fr> wrote:
> >>
> >> Hi Dmitry,
> >>
> >>> On Wed, Feb 17, 2021 at 5:36 PM Alex Ghiti <alex@ghiti.fr> 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@ghiti.fr> 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@google.com> wrote:
> >>>>>>>>
> >>>>>>>> On Fri, Jan 29, 2021 at 9:11 AM Dmitry Vyukov <dvyukov@google.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
> >>>>>>
> >>>>>> 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!

> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9b0592b11a9f..ff2495707edb 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -287,7 +287,7 @@ pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
>
> -#define MAX_EARLY_MAPPING_SIZE SZ_128M
> +#define MAX_EARLY_MAPPING_SIZE PGDIR_SIZE
>
> pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>
> --
> 2.20.1
>
> Thanks,
>
> Alex
>
> > scripts/config -d KASAN_INLINE -e KASAN_OUTLINE -d
> > CC_OPTIMIZE_FOR_PERFORMANCE -e CC_OPTIMIZE_FOR_SIZE
> > 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 boots fine, at least at to starting init process]
> >
> > _______________________________________________
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> >