Erik Schilling
2023-Sep-01 10:37 UTC
[BUG] virtio-fs: Corruption when running binaries from virtiofsd-backed fs
On Wed Aug 30, 2023 at 10:20 AM CEST, Erik Schilling wrote:> Hi all! > > Some days ago I posted to #virtiofs:matrix.org, describing that I am > observing what looks like a corruption when executing programs from a > virtiofs-based filesystem. > > Over the last few days I spent more time drilling into the problem. > This is an attempt at summarizing my findings in order to see what other > people think about this. > > When running binaries mounted from virtiofs they may either: fail with a > segfault, fail with badaddr, get stuck or - sometimes - succeed. > > Environment: > Host: Fedora 38 running 6.4.11-200.fc38.x86_64 > Guest: Yocto-based image: 6.4.9-yocto-standard, aarch64 > virtiofsd: latest main + some debug prints [1] > QEMU: built from recent git [2] > > virtiofsd invocation: > RUST_LOG="debug" ./virtiofsd --seccomp=none --sandbox=none \ > --socket-path "fs.sock0" --shared-dir $PWD/share-dir/ --cache=never > > QEMU invocation: > ~/projects/qemu/build/qemu-system-aarch64 -kernel Image -machine virt \ > -cpu cortex-a57 \ > -serial mon:stdio \ > -device virtio-net-pci,netdev=net0 \ > -netdev user,id=net0,hostfwd=tcp::2223-:22 \ > -display none -m 2048 -smp 4 \ > -object memory-backend-memfd,id=mem,size=2048M,share=on \ > -numa node,memdev=mem \ > -hda trs-overlay-guest.qcow2 \ > -chardev socket,id=char0,path="fs.sock0" \ > -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=/dev/root \ > -append 'root=/dev/vda2 ro log_buf_len=8M' > > I figured that launching virtiofsd with --cache=always masks the > problem. Therefore, I set --cache=never, but I think I observed no > difference compared to the default setting (auto). > > Adding logging to virtiofsd and kernel _feeled_ like it made the problem > harder to reproduce - leaving me with the impression that some race is > happening on somewhere. > > Trying to rule out that virtiofsd is returning corrupted data, I added > some logging and hashsum calculation hacks to it [1]. The hashes check > out across multiple accesses and the order and kind of queued messages > is exactly the same in both the error case and crash case. fio was also > unable to find any errors with a naive job description [3]. > > Next, I tried to capture info on the guest side. This became a bit > tricky since the crashes became pretty rare once I followed a fixed > pattern of starting log capture, running perf and trying to reproduce > the problem. Ultimately, I had the most consistent results with > immediately running a program twice: > > /mnt/ld-linux-aarch64.so.1 /mnt/ls.coreutils /; \ > /mnt/ld-linux-aarch64.so.1 /mnt/ls.coreutils / > > (/mnt being the virtiofs mount) > > For collecting logs, I made a hack to the guest kernel in order to dump > the page content after receiving the virtiofs responses [4]. Reproducing > the problem with this, leaves me with logs that seem to suggest that > virtiofsd is returning identical content, but the guest kernel seems to > receive differing pages: > > good-kernel [5]: > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x312 nodeid 0x1 in.len 56 out.len 104 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 1 unique 0x314 nodeid 0x1 in.len 53 out.len 128 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x316 nodeid 0x29 in.len 56 out.len 104 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 14 unique 0x318 nodeid 0x29 in.len 48 out.len 16 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 15 unique 0x31a nodeid 0x29 in.len 80 out.len 832 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs: page: 000000006996d520 > kernel: virtio_fs: to: 00000000de590c14 > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > [...] > > bad-kernel [6]: > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x162 nodeid 0x1 in.len 56 out.len 104 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 1 unique 0x164 nodeid 0x1 in.len 53 out.len 128 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x166 nodeid 0x16 in.len 56 out.len 104 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 14 unique 0x168 nodeid 0x16 in.len 48 out.len 16 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs_wake_pending_and_unlock: opcode 15 unique 0x16a nodeid 0x16 in.len 80 out.len 832 > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > kernel: virtio_fs: page: 000000006ce9a559 > kernel: virtio_fs: to: 000000007ae8b946 > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > kernel: virtio_fs rsp:80 40 de c8 ff ff 00 00 cc 2b 62 ae ff ff 00 00 . at .......+b..... > kernel: virtio_fs rsp:02 4e de c8 ff ff 00 00 00 00 00 00 00 00 00 00 .N.............. > [...] > > When looking at the corresponding output from virtiofsd, it claims to > have returned identical data: > > good-virtiofsd [7]: > [DEBUG virtiofsd::server] Received request: opcode=Read (15), inode=41, unique=794, pid=481 > [src/server.rs:618] r.read_obj().map_err(Error::DecodeMessage)? = ReadIn { > fh: 31, > offset: 0, > size: 832, > read_flags: 2, > lock_owner: 6838554705639967244, > flags: 131072, > padding: 0, > } > [src/file_traits.rs:161] hash = 2308490450751364994 > [DEBUG virtiofsd::server] Replying OK, header: OutHeader { len: 848, error: 0, unique: 794 } > > bad-virtiofsd [8]: > [DEBUG virtiofsd::server] Received request: opcode=Read (15), inode=22, unique=362, pid=406 > [src/server.rs:618] r.read_obj().map_err(Error::DecodeMessage)? = ReadIn { > fh: 12, > offset: 0, > size: 832, > read_flags: 2, > lock_owner: 6181120926258395554, > flags: 131072, > padding: 0, > } > [src/file_traits.rs:161] hash = 2308490450751364994 > [DEBUG virtiofsd::server] Replying OK, header: OutHeader { len: 848, error: 0, unique: 362 } > > The "corruption" only seems to happen in this one page, all other pages > are identical between runs (except that the bad run terminates earlier). > > What do the experts think here? To me it feels a bit like some kind of > corruption is going on. Or am I misinterpreting things here? > > Which further analysis steps would you suggest? > > > Further notes: > > After collecting the above results, I realized that running the guest > with -smp 1 makes the problems a lot worse. So maybe that is a better > choice when trying to reproduce it. > > Repo with my scripts is available at: > https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/ > > The scripts are just quick and dirty implementations and are not > particulary portable.Summary of my testing during the last few days: Testing with KCSAN revealed a few cases that look like missing READ_ONCE annotations (will send patches separately). But nothing of that was related to the immediate problem. I tested instrument_read() and another round of logging with a delay to virtio_fs_request_complete. It looks like the buffer get corrupted before entering that function. KCSAN or manual sleeps + prints did not show any corruption while in that function. KASAN did not report any issues. Patching virtiofsd to do an additional copy and going through rust-vmm's .copy_to() function did not change the behaviour. I will mostly be off next week, will continue analysis afterwards. Happy to hear about suggestions of other things to try :). Good weekend, - Erik> > - Erik > > [1] https://gitlab.com/ablu/virtiofsd/-/commit/18fd0c1849e15bc55fbdd6e1f169801b2b03da1f > [2] https://gitlab.com/qemu-project/qemu/-/commit/50e7a40af372ee5931c99ef7390f5d3d6fbf6ec4 > [3] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/397a6310dea35973025e3d61f46090bf0c092762/share-dir/write-and-verify-mmap.fio > [4] https://github.com/Ablu/linux/commit/3880b9f8affb01aeabb0a04fe76ad7701dc0bb95 > [5] Line 12923: https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/good-drop-bad-1.txt > [6] Line 12923: https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/good-bad-1.txt > [7] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/virtiofsd.txt#L2538-2549 > [8] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/virtiofsd.txt#L1052-1063
Erik Schilling
2023-Sep-13 06:18 UTC
[BUG] virtio-fs: Corruption when running binaries from virtiofsd-backed fs
On Fri Sep 1, 2023 at 12:37 PM CEST, Erik Schilling wrote:> On Wed Aug 30, 2023 at 10:20 AM CEST, Erik Schilling wrote: > > Hi all! > > > > Some days ago I posted to #virtiofs:matrix.org, describing that I am > > observing what looks like a corruption when executing programs from a > > virtiofs-based filesystem. > > > > Over the last few days I spent more time drilling into the problem. > > This is an attempt at summarizing my findings in order to see what other > > people think about this. > > > > When running binaries mounted from virtiofs they may either: fail with a > > segfault, fail with badaddr, get stuck or - sometimes - succeed. > > > > Environment: > > Host: Fedora 38 running 6.4.11-200.fc38.x86_64 > > Guest: Yocto-based image: 6.4.9-yocto-standard, aarch64 > > virtiofsd: latest main + some debug prints [1] > > QEMU: built from recent git [2] > > > > virtiofsd invocation: > > RUST_LOG="debug" ./virtiofsd --seccomp=none --sandbox=none \ > > --socket-path "fs.sock0" --shared-dir $PWD/share-dir/ --cache=never > > > > QEMU invocation: > > ~/projects/qemu/build/qemu-system-aarch64 -kernel Image -machine virt \ > > -cpu cortex-a57 \ > > -serial mon:stdio \ > > -device virtio-net-pci,netdev=net0 \ > > -netdev user,id=net0,hostfwd=tcp::2223-:22 \ > > -display none -m 2048 -smp 4 \ > > -object memory-backend-memfd,id=mem,size=2048M,share=on \ > > -numa node,memdev=mem \ > > -hda trs-overlay-guest.qcow2 \ > > -chardev socket,id=char0,path="fs.sock0" \ > > -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=/dev/root \ > > -append 'root=/dev/vda2 ro log_buf_len=8M' > > > > I figured that launching virtiofsd with --cache=always masks the > > problem. Therefore, I set --cache=never, but I think I observed no > > difference compared to the default setting (auto). > > > > Adding logging to virtiofsd and kernel _feeled_ like it made the problem > > harder to reproduce - leaving me with the impression that some race is > > happening on somewhere. > > > > Trying to rule out that virtiofsd is returning corrupted data, I added > > some logging and hashsum calculation hacks to it [1]. The hashes check > > out across multiple accesses and the order and kind of queued messages > > is exactly the same in both the error case and crash case. fio was also > > unable to find any errors with a naive job description [3]. > > > > Next, I tried to capture info on the guest side. This became a bit > > tricky since the crashes became pretty rare once I followed a fixed > > pattern of starting log capture, running perf and trying to reproduce > > the problem. Ultimately, I had the most consistent results with > > immediately running a program twice: > > > > /mnt/ld-linux-aarch64.so.1 /mnt/ls.coreutils /; \ > > /mnt/ld-linux-aarch64.so.1 /mnt/ls.coreutils / > > > > (/mnt being the virtiofs mount) > > > > For collecting logs, I made a hack to the guest kernel in order to dump > > the page content after receiving the virtiofs responses [4]. Reproducing > > the problem with this, leaves me with logs that seem to suggest that > > virtiofsd is returning identical content, but the guest kernel seems to > > receive differing pages: > > > > good-kernel [5]: > > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x312 nodeid 0x1 in.len 56 out.len 104 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 1 unique 0x314 nodeid 0x1 in.len 53 out.len 128 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x316 nodeid 0x29 in.len 56 out.len 104 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 14 unique 0x318 nodeid 0x29 in.len 48 out.len 16 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 15 unique 0x31a nodeid 0x29 in.len 80 out.len 832 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs: page: 000000006996d520 > > kernel: virtio_fs: to: 00000000de590c14 > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > [...] > > > > bad-kernel [6]: > > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x162 nodeid 0x1 in.len 56 out.len 104 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 1 unique 0x164 nodeid 0x1 in.len 53 out.len 128 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 3 unique 0x166 nodeid 0x16 in.len 56 out.len 104 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 14 unique 0x168 nodeid 0x16 in.len 48 out.len 16 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs_wake_pending_and_unlock: opcode 15 unique 0x16a nodeid 0x16 in.len 80 out.len 832 > > kernel: virtiofs virtio1: virtio_fs_vq_done requests.0 > > kernel: virtio_fs: page: 000000006ce9a559 > > kernel: virtio_fs: to: 000000007ae8b946 > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > kernel: virtio_fs rsp:00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > kernel: virtio_fs rsp:80 40 de c8 ff ff 00 00 cc 2b 62 ae ff ff 00 00 . at .......+b..... > > kernel: virtio_fs rsp:02 4e de c8 ff ff 00 00 00 00 00 00 00 00 00 00 .N.............. > > [...] > > > > When looking at the corresponding output from virtiofsd, it claims to > > have returned identical data: > > > > good-virtiofsd [7]: > > [DEBUG virtiofsd::server] Received request: opcode=Read (15), inode=41, unique=794, pid=481 > > [src/server.rs:618] r.read_obj().map_err(Error::DecodeMessage)? = ReadIn { > > fh: 31, > > offset: 0, > > size: 832, > > read_flags: 2, > > lock_owner: 6838554705639967244, > > flags: 131072, > > padding: 0, > > } > > [src/file_traits.rs:161] hash = 2308490450751364994 > > [DEBUG virtiofsd::server] Replying OK, header: OutHeader { len: 848, error: 0, unique: 794 } > > > > bad-virtiofsd [8]: > > [DEBUG virtiofsd::server] Received request: opcode=Read (15), inode=22, unique=362, pid=406 > > [src/server.rs:618] r.read_obj().map_err(Error::DecodeMessage)? = ReadIn { > > fh: 12, > > offset: 0, > > size: 832, > > read_flags: 2, > > lock_owner: 6181120926258395554, > > flags: 131072, > > padding: 0, > > } > > [src/file_traits.rs:161] hash = 2308490450751364994 > > [DEBUG virtiofsd::server] Replying OK, header: OutHeader { len: 848, error: 0, unique: 362 } > > > > The "corruption" only seems to happen in this one page, all other pages > > are identical between runs (except that the bad run terminates earlier). > > > > What do the experts think here? To me it feels a bit like some kind of > > corruption is going on. Or am I misinterpreting things here? > > > > Which further analysis steps would you suggest? > > > > > > Further notes: > > > > After collecting the above results, I realized that running the guest > > with -smp 1 makes the problems a lot worse. So maybe that is a better > > choice when trying to reproduce it. > > > > Repo with my scripts is available at: > > https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/ > > > > The scripts are just quick and dirty implementations and are not > > particulary portable. > > Summary of my testing during the last few days: > > Testing with KCSAN revealed a few cases that look like missing READ_ONCE > annotations (will send patches separately). But nothing of that was > related to the immediate problem. I tested instrument_read() and another > round of logging with a delay to virtio_fs_request_complete. It looks > like the buffer get corrupted before entering that function. KCSAN > or manual sleeps + prints did not show any corruption while in that > function. > > KASAN did not report any issues. > > Patching virtiofsd to do an additional copy and going through rust-vmm's > .copy_to() function did not change the behaviour. > > I will mostly be off next week, will continue analysis afterwards. Happy > to hear about suggestions of other things to try :).Back from a week of vacation... Summary of what was discussed on #virtiofs:matrix.org: The issue only seems to happen in QEMU TCG scenarios (I tested aarch64 and x86_64 on x86_64, wizzard on Matrix tested arm32). CCing qemu-devel. Maybe someone has some hints on where to focus the debugging efforts? I am trying to build a complex monster script of tracing the relevant addresses in order to figure out whether the guest or host does the writes. But I am happy to hear about more clever ideas :). - Erik> > Good weekend, > > - Erik > > > > > > - Erik > > > > [1] https://gitlab.com/ablu/virtiofsd/-/commit/18fd0c1849e15bc55fbdd6e1f169801b2b03da1f > > [2] https://gitlab.com/qemu-project/qemu/-/commit/50e7a40af372ee5931c99ef7390f5d3d6fbf6ec4 > > [3] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/397a6310dea35973025e3d61f46090bf0c092762/share-dir/write-and-verify-mmap.fio > > [4] https://github.com/Ablu/linux/commit/3880b9f8affb01aeabb0a04fe76ad7701dc0bb95 > > [5] Line 12923: https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/good-drop-bad-1.txt > > [6] Line 12923: https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/good-bad-1.txt > > [7] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/virtiofsd.txt#L2538-2549 > > [8] https://git.codelinaro.org/erik_schilling/jira-orko-65-bootstrap-k3s-config/-/blob/main/logs/2023-08-29%2013%3A42%3A35%2B02%3A00/virtiofsd.txt#L1052-1063