Message-ID: <b5f3a8b7-e913-2272-115a-677edd35a485@redhat.com>
Date:   Mon, 16 Aug 2021 21:20:23 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [BUG] general protection fault when reading /proc/kcore

On 16.08.21 21:12, Mike Rapoport wrote:
> On Mon, Aug 16, 2021 at 08:38:43PM +0200, David Hildenbrand wrote:
>> 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@...alhost ~]# cat /proc/kallsyms | grep ksys_read
>>>> ffffffff8927a800 T ksys_readahead
>>>> ffffffff89333660 T ksys_read
>>>>
>>>> [root@...alhost ~]# 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
> 
> With Jiri's config and '-cpu <very long string>' it triggers for me on
> v5.14-rc6.
> 
> I'll also try to take a look tomorrow.

No luck here on my AMD system, even with that '-cpu <very long string>'. 
Maybe some relevant CPU features get silently ignored because they are 
not actually available on my system.

-- 
Thanks,

David / dhildenb

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