Messages in this thread | | | From | Dmitry Vyukov <> | Date | Wed, 17 Feb 2021 05:42:16 +0100 | Subject | Re: riscv+KASAN does not boot |
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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). 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.
> > 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 > >
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