[PATCH -fixes v2 4/4] riscv: Fix config KASAN && DEBUG_VIRTUAL

Thu Feb 24 19:57:45 PST 2022

On Wed, 23 Feb 2022 09:17:16 PST (-0800), alexandre.ghiti at canonical.com wrote:
> On Wed, Feb 23, 2022 at 2:10 PM Alexandre Ghiti
> <alexandre.ghiti at canonical.com> wrote:
>>
>> Hi Aleksandr,
>>
>> On Tue, Feb 22, 2022 at 11:28 AM Aleksandr Nogikh <nogikh at google.com> wrote:
>> >
>> > Hi Alexandre,
>> >
>> > Thanks for the series!
>> >
>> > However, I still haven't managed to boot the kernel. What I did:
>> > 1) Checked out the riscv/fixes branch (this is the one we're using on
>> > syzbot). The latest commit was
>> > 6df2a016c0c8a3d0933ef33dd192ea6606b115e3.
>> > 2) Applied all 4 patches.
>> > 3) Used the config from the cover letter:
>> > https://gist.github.com/a-nogikh/279c85c2d24f47efcc3e865c08844138
>> > 4) Built with `make -j32 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-`
>> > 5) Ran with `qemu-system-riscv64 -m 2048 -smp 1 -nographic -no-reboot
>> > -device virtio-rng-pci -machine virt -device
>> > virtio-net-pci,netdev=net0 -netdev
>> > user,id=net0,restrict=on,hostfwd=tcp:127.0.0.1:12529-:22 -device
>> > virtio-blk-device,drive=hd0 -drive
>> > file=~/kernel-image/riscv64,if=none,format=raw,id=hd0 -snapshot
>> > -kernel ~/linux-riscv/arch/riscv/boot/Image -append "root=/dev/vda
>> > console=ttyS0 earlyprintk=serial"` (this is similar to how syzkaller
>> > runs qemu).
>> >
>> > Can you please hint at what I'm doing differently?
>>
>> A short summary of what I found to keep you updated:
>>
>> I compared your command line and mine, the differences are that I use
>> "smp=4" and I add "earlycon" to the kernel command line. When added to
>> your command line, that allows it to boot. I understand why it helps
>> but I can't explain what's wrong...Anyway, I fixed a warning that I
>> had missed and that allows me to remove the "smp=4" and "earlycon".
>>
>> But this is not over yet...Your command line still does not allow to
>> reach userspace, it fails with the following stacktrace:
>>
>> [   11.537817][    T1] Unable to handle kernel paging request at
>> virtual address fffff5eeffffc800
>> [   11.539450][    T1] Oops [#1]
>> [   11.539909][    T1] Modules linked in:
>> [   11.540451][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
>> 5.17.0-rc1-00007-ga68b89289e26-dirty #28
>> [   11.541364][    T1] Hardware name: riscv-virtio,qemu (DT)
>> [   11.542032][    T1] epc : kasan_check_range+0x96/0x13e
>> [   11.542654][    T1]  ra : memset+0x1e/0x4c
>> [   11.543388][    T1] epc : ffffffff8046c312 ra : ffffffff8046ca16 sp
>> : ffffaf8007337b70
>> [   11.544037][    T1]  gp : ffffffff85866c80 tp : ffffaf80073d8000 t0
>> : 0000000000046000
>> [   11.544637][    T1]  t1 : fffff5eeffffc9ff t2 : 0000000000000000 s0
>> : ffffaf8007337ba0
>> [   11.545409][    T1]  s1 : 0000000000001000 a0 : fffff5eeffffca00 a1
>> : 0000000000001000
>> [   11.546072][    T1]  a2 : 0000000000000001 a3 : ffffffff8039ef24 a4
>> : ffffaf7ffffe4000
>> [   11.546707][    T1]  a5 : fffff5eeffffc800 a6 : 0000004000000000 a7
>> : ffffaf7ffffe4fff
>> [   11.547541][    T1]  s2 : ffffaf7ffffe4000 s3 : 0000000000000000 s4
>> : ffffffff8467faa8
>> [   11.548277][    T1]  s5 : 0000000000000000 s6 : ffffffff85869840 s7
>> : 0000000000000000
>> [   11.548950][    T1]  s8 : 0000000000001000 s9 : ffffaf805a54a048
>> s10: ffffffff8588d420
>> [   11.549705][    T1]  s11: ffffaf7ffffe4000 t3 : 0000000000000000 t4
>> : 0000000000000040
>> [   11.550465][    T1]  t5 : fffff5eeffffca00 t6 : 0000000000000002
>> [   11.551131][    T1] status: 0000000000000120 badaddr:
>> fffff5eeffffc800 cause: 000000000000000d
>> [   11.551961][    T1] [<ffffffff8039ef24>] pcpu_alloc+0x84a/0x125c
>> [   11.552928][    T1] [<ffffffff8039f994>] __alloc_percpu+0x28/0x34
>> [   11.553555][    T1] [<ffffffff83286954>] ip_rt_init+0x15a/0x35c
>> [   11.554128][    T1] [<ffffffff83286d24>] ip_init+0x18/0x30
>> [   11.554642][    T1] [<ffffffff8328844a>] inet_init+0x2a6/0x550
>> [   11.555428][    T1] [<ffffffff80003220>] do_one_initcall+0x132/0x7e4
>> [   11.556049][    T1] [<ffffffff83201f7a>] kernel_init_freeable+0x510/0x5b4
>> [   11.556771][    T1] [<ffffffff831424e4>] kernel_init+0x28/0x21c
>> [   11.557344][    T1] [<ffffffff800056a0>] ret_from_exception+0x0/0x14
>> [   11.585469][    T1] ---[ end trace 0000000000000000 ]---
>>
>> 0xfffff5eeffffc800 is a KASAN address that points to the very end of
>> vmalloc address range, which is weird since KASAN_VMALLOC is not
>> enabled.
>> Moreover my command line does not trigger the above bug, and I'm
>> trying to understand why:
>
> When I read this email I saw that I did not use the same qemu version:
> I have a locally built version that disables sv48, which is the one
> that works so the problem came from the sv48 support.
>
> In a nutshell, the issue comes from the fact that kasan inner regions
> are not aligned on PGDIR_SIZE when sv48 (which is 4-level page table)
> is on, and then when populating the kasan linear mapping region, that
> clears the kasan vmalloc region which is in the same PGD: the fix is
> to copy its content before initializing the linear mapping entries.
> This issue only happens when KASAN_VMALLOC is disabled. I had fixed
> this already for kasan_shallow_populate_pud, but missed
> kasan_populate_pud.
>
> Tomorrow I'll push the v3. It still does not fix the issue I describe
> in the cover letter though, so still more work to do. At least, I was
> able to reach userspace with your *exact* qemu command :)

I can't find a v3.

>
> Alex
>
>
>>
>> /home/alex/work/qemu/build/riscv64-softmmu/qemu-system-riscv64 -M virt
>> -bios /home/alex/work/opensbi/build/platform/generic/firmware/fw_dynamic.bin
>> -kernel /home/alex/work/kernel-build/riscv_rv64_kernel/arch/riscv/boot/Image
>> -netdev user,id=net0 -device virtio-net-device,netdev=net0 -drive
>> file=/home/alex/work/kernel-build/rootfs.ext2,format=raw,id=hd0
>> -device virtio-blk-device,drive=hd0 -nographic -smp 4 -m 16G -s
>> -append "rootwait earlycon root=/dev/vda ro earlyprintk=serial"
>>
>> I'm looking into all of this and will get back with a v3 soon :)
>>
>> Thanks,
>>
>> Alex
>>
>>
>>
>>
>>
>>
>> >
>> > A simple config with KASAN, KASAN_OUTLINE and DEBUG_VIRTUAL now indeed
>> > leads to a booting kernel, which was not the case before.
>> > make defconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
>> > ./scripts/config -e KASAN -e KASAN_OUTLINE -e DEBUG_VIRTUAL
>> > make olddefconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
>> >
>> > --
>> > Best Regards,
>> > Aleksandr
>> >
>> > On Mon, Feb 21, 2022 at 5:17 PM Alexandre Ghiti
>> > <alexandre.ghiti at canonical.com> wrote:
>> > >
>> > > __virt_to_phys function is called very early in the boot process (ie
>> > > kasan_early_init) so it should not be instrumented by KASAN otherwise it
>> > > bugs.
>> > >
>> > > Fix this by declaring phys_addr.c as non-kasan instrumentable.
>> > >
>> > > Signed-off-by: Alexandre Ghiti <alexandre.ghiti at canonical.com>
>> > > ---
>> > >  arch/riscv/mm/Makefile | 3 +++
>> > >  1 file changed, 3 insertions(+)
>> > >
>> > > diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
>> > > index 7ebaef10ea1b..ac7a25298a04 100644
>> > > --- a/arch/riscv/mm/Makefile
>> > > +++ b/arch/riscv/mm/Makefile
>> > > @@ -24,6 +24,9 @@ obj-$(CONFIG_KASAN)   += kasan_init.o
>> > >  ifdef CONFIG_KASAN
>> > >  KASAN_SANITIZE_kasan_init.o := n
>> > >  KASAN_SANITIZE_init.o := n
>> > > +ifdef CONFIG_DEBUG_VIRTUAL
>> > > +KASAN_SANITIZE_physaddr.o := n
>> > > +endif
>> > >  endif
>> > >
>> > >  obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
>> > > --
>> > > 2.32.0
>> > >