Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 16 Feb 2021 14:45:08 +0100 | Subject | Re: riscv+KASAN does not boot |
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On Tue, Feb 16, 2021 at 12:25 PM Dmitry Vyukov <dvyukov@google.com> wrote: > > 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 > > > > 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 > > 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 am debugging the next issue with VDSO. clock_gettime is broken in some weird way. syzkaller has this function:
static uint64 current_time_ms(void) { struct timespec ts; if (clock_gettime(CLOCK_MONOTONIC, &ts)) //if (syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts)) fail("clock_gettime failed"); return (uint64)ts.tv_sec * 1000 + (uint64)ts.tv_nsec / 1000000; }
When using clock_gettime it producer some nonsense that breaks all timeouts (in particular monotonic time goes backwards): pid=4343 now=836038064151457975 pid=4343 now=836038064151457975 pid=4343 now=836038064151457970 pid=4343 now=836038064151457971
When I tested it calling real syscall, it works as expected: pid=4876 now=2493379 pid=4876 now=2493392 pid=4876 now=2493395 pid=4876 now=2493409 pid=4876 now=2493414
Is it a known issue? Any ideas?
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