Messages in this thread | | | Subject | Re: riscv+KASAN does not boot | From | Alex Ghiti <> | Date | Wed, 17 Feb 2021 11:36:40 -0500 |
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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
Thanks,
> >>> Then trying to boot it using: >>> QEMU emulator version 5.2.0 (Debian 1:5.2+dfsg-3) >>> $ qemu-system-riscv64 -machine virt -smp 2 -m 4G ... >>> >>> It shows no output from the kernel whatsoever, even though I have >>> earlycon and output shows very early with other configs. >>> Kernel boots fine with defconfig and other smaller configs. >>> >>> If I enable KASAN_OUTLINE and CC_OPTIMIZE_FOR_SIZE, then this config >>> also boots fine. Both of these options significantly reduce kernel >>> size. However, I can also boot the kernel without these 2 configs, if >>> I disable a whole lot of subsystem configs. This makes me think that >>> there is an issue related to kernel size somewhere in >>> qemu/bootloader/kernel bootstrap code. >>> Does it make sense to you? Can somebody reproduce what I am seeing? > >> >> I did not bring any answer to your question, but at least you know I'm >> working on it, I'll keep you posted. >> >> Thanks for taking the time to setup syzkaller. >> >> Alex >> >>> Thanks >>> >>> _______________________________________________ >>> linux-riscv mailing list >>> linux-riscv@lists.infradead.org >>> http://lists.infradead.org/mailman/listinfo/linux-riscv >>> > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv >
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