Re: [BUG] general protection fault when reading /proc/kcore

[David Hildenbrand <david@redhat.com>]

On 16.08.21 20:12, Jiri Olsa wrote:
> On Mon, Aug 16, 2021 at 07:49:15PM +0200, David Hildenbrand wrote:
>> On 16.08.21 19:34, Jiri Olsa wrote:
>>> hi,
>>> I'm getting fault below when running:
>>>
>>> 	# cat /proc/kallsyms | grep ksys_read
>>> 	ffffffff8136d580 T ksys_read
>>> 	# objdump -d --start-address=0xffffffff8136d580 --stop-address=0xffffffff8136d590 /proc/kcore
>>>
>>> 	/proc/kcore:     file format elf64-x86-64
>>>
>>> 	Segmentation fault
>>>
>>> any idea? config is attached
>>
>> Just tried with a different config on 5.14.0-rc6+
>>
>> [root@localhost ~]# cat /proc/kallsyms | grep ksys_read
>> ffffffff8927a800 T ksys_readahead
>> ffffffff89333660 T ksys_read
>>
>> [root@localhost ~]# objdump -d --start-address=0xffffffff89333660
>> --stop-address=0xffffffff89333670
>>
>> a.out:     file format elf64-x86-64
>>
>>
>>
>> The kern_addr_valid(start) seems to fault in your case, which is weird,
>> because it merely walks the page tables. But it seems to complain about a
>> non-canonical address 0xf887ffcbff000
>>
>> Can you post your QEMU cmdline? Did you test this on other kernel versions?
> 
> I'm using virt-manager so:
> 
> /usr/bin/qemu-system-x86_64 -name guest=fedora33,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-13-fedora33/master-key.aes -machine pc-q35-5.1,accel=kvm,usb=off,vmport=off,dump-guest-core=off,memory-backend=pc.ram -cpu Skylake-Server-IBRS,ss=on,vmx=on,pdcm=on,hypervisor=on,tsc-adjust=on,clflushopt=on,umip=on,pku=on,stibp=on,arch-capabilities=on,ssbd=on,xsaves=on,ibpb=on,amd-stibp=on,amd-ssbd=on,skip-l1dfl-vmentry=on,pschange-mc-no=on -m 8192 -object memory-backend-ram,id=pc.ram,size=8589934592 -overcommit mem-lock=off -smp 20,sockets=20,cores=1,threads=1 -uuid 2185d5a9-dbad-4d61-aa4e-97af9fd7ebca -no-user-config -nodefaults -chardev socket,id=charmonitor,fd=36,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global ICH9-LPC.disable_s3=1 -global ICH9-LPC.disable_s4=1 -boot strict=on -kernel /home/jolsa/qemu/run/vmlinux -initrd /home/jolsa/qemu/run/initrd -append root=/dev/mapper/fedora_fedora-root ro rd.lvm.lv=fedora_fedora/root console=tty0 console=ttyS0,115200 -device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 -device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 -device pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 -device pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 -device pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 -device pcie-root-port,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 -device pcie-root-port,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 -device qemu-xhci,p2=15,p3=15,id=usb,bus=pci.2,addr=0x0 -device virtio-serial-pci,id=virtio-serial0,bus=pci.3,addr=0x0 -blockdev {"driver":"file","filename":"/var/lib/libvirt/images/fedora33.qcow2","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"} -blockdev {"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":null} -device virtio-blk-pci,bus=pci.4,addr=0x0,drive=libvirt-2-format,id=virtio-disk0,bootindex=1 -device ide-cd,bus=ide.0,id=sata0-0-0 -netdev tap,fd=38,id=hostnet0,vhost=on,vhostfd=39 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:f3:c6:e7,bus=pci.1,addr=0x0 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -chardev socket,id=charchannel0,fd=40,server,nowait -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0 -chardev spicevmc,id=charchannel1,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0 -device usb-tablet,id=input0,bus=usb.0,port=1 -spice port=5900,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pcie.0,addr=0x1 -device ich9-intel-hda,id=sound0,bus=pcie.0,addr=0x1b -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev spicevmc,id=charredir0,name=usbredir -device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev spicevmc,id=charredir1,name=usbredir -device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device virtio-balloon-pci,id=balloon0,bus=pci.5,addr=0x0 -object rng-random,id=objrng0,filename=/dev/urandom -device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.6,addr=0x0 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on
> 
> so far I tested just bpf-next/master:
>    git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
> 

Just tried with upstream Linux (5.14.0-rc6) and your config without 
triggering it. I'm using "-cpu host", though, on an AMD Ryzen 9 3900X

> and jsut removed my changes to make sure it wasn't me ;-)

:)

> 
> I'll try to find a version that worked for me before

Can you try with upstream Linux as well?


-- 
Thanks,

David / dhildenb