| Message ID | 20231020104250.9537-1-flaniel@linux.microsoft.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Return EADDRNOTAVAIL when func matches several symbols during kprobe creation | expand |
Hi, Thanks for update the series. The series looks good to me. Let me pick those in probes/fixes. Thank you! On Fri, 20 Oct 2023 13:42:48 +0300 Francis Laniel <flaniel@linux.microsoft.com> wrote: > Hi. > > > In the kernel source code, it exists different functions which share the same > name but which have, of course, different addresses as they can be defined in > different modules: > # Kernel was compiled with CONFIG_NTFS_FS and CONFIG_NTFS3_FS as built-in. > root@vm-amd64:~# grep ntfs_file_write_iter /proc/kallsyms > ffffffff814ce3c0 t __pfx_ntfs_file_write_iter > ffffffff814ce3d0 t ntfs_file_write_iter > ffffffff814fc8a0 t __pfx_ntfs_file_write_iter > ffffffff814fc8b0 t ntfs_file_write_iter > This can be source of troubles when you create a PMU kprobe for such a function, > as it will only install one for the first address (e.g. 0xffffffff814ce3d0 in > the above). > This could lead to some troubles were BPF based tools does not report any event > because the second function is not called: > root@vm-amd64:/mnt# mount | grep /mnt > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > # ig is a tool which installs a PMU kprobe on ntfs_file_write_iter(). > root@vm-amd64:/mnt# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > [1] 207 > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > 3+0 records in > 3+0 records out > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00543323 s, 283 kB/s > root@vm-amd64:/mnt# fg > ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo > ^Croot@vm-amd64:/mnt# more /tmp/foo > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > T BYTES OFFSET LAT FILE > 214 dd > R 512 0 766 foo > 214 dd > R 512 512 9 foo > 214 dd > As you can see in the above, only read events are reported and no write because > the kprobe is installed for the old ntfs_file_write_iter() and not the ntfs3 > one. > The same behavior occurs with sysfs kprobe: > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > /sys/kernel/tracing/kprobe_events > root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events > p:probe/ntfs_file_write_iter ntfs_file_write_iter > root@vm-amd64:/# mount | grep /mnt > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > root@vm-amd64:/# perf record -e probe:ntfs_file_write_iter & > [1] 210 > root@vm-amd64:/# cd /mnt/ > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > 3+0 records in > 3+0 records out > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00234793 s, 654 kB/s > root@vm-amd64:/mnt# cd - > / > root@vm-amd64:/# fg > perf record -e probe:ntfs_file_write_iter > ^C[ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.056 MB perf.data ] > > root@vm-amd64:/# perf report > Error: > The perf.data data has no samples! > # To display the perf.data header info, please use --header/--header-only optio> > # > > In this contribution, I modified the functions creating sysfs and PMU kprobes to > test if the function name given as argument matches several symbols. > In this case, these functions return EADDRNOTAVAIL to indicate the user to use > addr and offs to remove this ambiguity. > So, when the above BPF tool is run, the following error message is printed: > root@vm-amd64:~# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > [1] 228 > root@vm-amd64:~# more /tmp/foo > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > T BYTES OFFSET LAT FILE > Error: running gadget: running gadget: installing tracer: attaching kprobe: crea > ting perf_kprobe PMU (arch-specific fallback for "ntfs_file_write_iter"): token > ntfs_file_write_iter: opening perf event: cannot assign requested address > And the same with sysfs kprobe: > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > /sys/kernel/tracing/kprobe_events > -bash: echo: write error: Cannot assign requested address > Note that, this does not influence perf as it installs kprobes as offset on > _text: > root@vm-amd64:/# perf probe --add ntfs_file_write_iter > Added new events: > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > ... > root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events > p:probe/ntfs_file_write_iter _text+5039088 > p:probe/ntfs_file_write_iter _text+5228752 > > Note that, this contribution is the conclusion of a previous RFC which intended > to install a PMU kprobe for all matching symbols [1, 2]. > > If you see any way to improve this contribution, please share your feedback. > > Changes since: > v1: > * Use EADDRNOTAVAIL instead of adding a new error code. > * Correct also this behavior for sysfs kprobe. > v2: > * Count the number of symbols corresponding to function name and return > EADDRNOTAVAIL if higher than 1. > * Return ENOENT if above count is 0, as it would be returned later by while > registering the kprobe. > v3: > * Check symbol does not contain ':' before testing its uniqueness. > * Add a selftest to check this is not possible to install a kprobe for a non > unique symbol. > v5: > * No changes, just add linux-stable as recipient. > v6: > * Rephrase commit message. > * Add "Cc:" to stable. > > Francis Laniel (2): > tracing/kprobes: Return EADDRNOTAVAIL when func matches several > symbols > selftests/ftrace: Add new test case which checks non unique symbol > > kernel/trace/trace_kprobe.c | 63 +++++++++++++++++++ > kernel/trace/trace_probe.h | 1 + > .../test.d/kprobe/kprobe_non_uniq_symbol.tc | 13 ++++ > 3 files changed, 77 insertions(+) > create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc > > Best regards and thank you in advance. > --- > [1]: https://lore.kernel.org/lkml/20230816163517.112518-1-flaniel@linux.microsoft.com/ > [2]: https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kernel.org/ > -- > 2.34.1 >
Hi! Le vendredi 20 octobre 2023, 15:12:39 EEST Masami Hiramatsu a écrit : > Hi, > > Thanks for update the series. The series looks good to me. > Let me pick those in probes/fixes. Thank you for picking it and all the good advices during the development process! > Thank you! Best regards. > On Fri, 20 Oct 2023 13:42:48 +0300 > > Francis Laniel <flaniel@linux.microsoft.com> wrote: > > Hi. > > > > > > In the kernel source code, it exists different functions which share the > > same name but which have, of course, different addresses as they can be > > defined in different modules: > > # Kernel was compiled with CONFIG_NTFS_FS and CONFIG_NTFS3_FS as built-in. > > root@vm-amd64:~# grep ntfs_file_write_iter /proc/kallsyms > > ffffffff814ce3c0 t __pfx_ntfs_file_write_iter > > ffffffff814ce3d0 t ntfs_file_write_iter > > ffffffff814fc8a0 t __pfx_ntfs_file_write_iter > > ffffffff814fc8b0 t ntfs_file_write_iter > > This can be source of troubles when you create a PMU kprobe for such a > > function, as it will only install one for the first address (e.g. > > 0xffffffff814ce3d0 in the above). > > This could lead to some troubles were BPF based tools does not report any > > event because the second function is not called: > > root@vm-amd64:/mnt# mount | grep /mnt > > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > > # ig is a tool which installs a PMU kprobe on ntfs_file_write_iter(). > > root@vm-amd64:/mnt# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > > [1] 207 > > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > > 3+0 records in > > 3+0 records out > > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00543323 s, 283 kB/s > > root@vm-amd64:/mnt# fg > > ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo > > ^Croot@vm-amd64:/mnt# more /tmp/foo > > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > > > > T BYTES OFFSET LAT FILE > > > > 214 dd > > > > R 512 0 766 foo > > > > 214 dd > > > > R 512 512 9 foo > > > > 214 dd > > > > As you can see in the above, only read events are reported and no write > > because the kprobe is installed for the old ntfs_file_write_iter() and > > not the ntfs3 one. > > The same behavior occurs with sysfs kprobe: > > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > > > /sys/kernel/tracing/kprobe_events root@vm-amd64:/# cat > > /sys/kernel/tracing/kprobe_events > > p:probe/ntfs_file_write_iter ntfs_file_write_iter > > root@vm-amd64:/# mount | grep /mnt > > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > > root@vm-amd64:/# perf record -e probe:ntfs_file_write_iter & > > [1] 210 > > root@vm-amd64:/# cd /mnt/ > > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > > 3+0 records in > > 3+0 records out > > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00234793 s, 654 kB/s > > root@vm-amd64:/mnt# cd - > > / > > root@vm-amd64:/# fg > > perf record -e probe:ntfs_file_write_iter > > ^C[ perf record: Woken up 1 times to write data ] > > [ perf record: Captured and wrote 0.056 MB perf.data ] > > > > root@vm-amd64:/# perf report > > Error: > > The perf.data data has no samples! > > # To display the perf.data header info, please use --header/--header-only > > optio> # > > > > In this contribution, I modified the functions creating sysfs and PMU > > kprobes to test if the function name given as argument matches several > > symbols. In this case, these functions return EADDRNOTAVAIL to indicate > > the user to use addr and offs to remove this ambiguity. > > So, when the above BPF tool is run, the following error message is > > printed: > > root@vm-amd64:~# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > > [1] 228 > > root@vm-amd64:~# more /tmp/foo > > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > > > > T BYTES OFFSET LAT FILE > > > > Error: running gadget: running gadget: installing tracer: attaching > > kprobe: crea ting perf_kprobe PMU (arch-specific fallback for > > "ntfs_file_write_iter"): token ntfs_file_write_iter: opening perf event: > > cannot assign requested address And the same with sysfs kprobe: > > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > > > /sys/kernel/tracing/kprobe_events -bash: echo: write error: Cannot > > assign requested address > > Note that, this does not influence perf as it installs kprobes as offset > > on > > _text: > > root@vm-amd64:/# perf probe --add ntfs_file_write_iter > > > > Added new events: > > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > > > > ... > > root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events > > p:probe/ntfs_file_write_iter _text+5039088 > > p:probe/ntfs_file_write_iter _text+5228752 > > > > Note that, this contribution is the conclusion of a previous RFC which > > intended to install a PMU kprobe for all matching symbols [1, 2]. > > > > If you see any way to improve this contribution, please share your > > feedback.> > > Changes since: > > v1: > > * Use EADDRNOTAVAIL instead of adding a new error code. > > * Correct also this behavior for sysfs kprobe. > > > > v2: > > * Count the number of symbols corresponding to function name and return > > EADDRNOTAVAIL if higher than 1. > > * Return ENOENT if above count is 0, as it would be returned later by > > while > > registering the kprobe. > > > > v3: > > * Check symbol does not contain ':' before testing its uniqueness. > > * Add a selftest to check this is not possible to install a kprobe for a > > non unique symbol. > > > > v5: > > * No changes, just add linux-stable as recipient. > > > > v6: > > * Rephrase commit message. > > * Add "Cc:" to stable. > > > > Francis Laniel (2): > > tracing/kprobes: Return EADDRNOTAVAIL when func matches several > > > > symbols > > > > selftests/ftrace: Add new test case which checks non unique symbol > > > > kernel/trace/trace_kprobe.c | 63 +++++++++++++++++++ > > kernel/trace/trace_probe.h | 1 + > > .../test.d/kprobe/kprobe_non_uniq_symbol.tc | 13 ++++ > > 3 files changed, 77 insertions(+) > > create mode 100644 > > tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc> > > Best regards and thank you in advance. > > --- > > [1]: > > https://lore.kernel.org/lkml/20230816163517.112518-1-flaniel@linux.micros > > oft.com/ [2]: > > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kern > > el.org/ -- > > 2.34.1
Hi. In the kernel source code, it exists different functions which share the same name but which have, of course, different addresses as they can be defined in different modules: # Kernel was compiled with CONFIG_NTFS_FS and CONFIG_NTFS3_FS as built-in. root@vm-amd64:~# grep ntfs_file_write_iter /proc/kallsyms ffffffff814ce3c0 t __pfx_ntfs_file_write_iter ffffffff814ce3d0 t ntfs_file_write_iter ffffffff814fc8a0 t __pfx_ntfs_file_write_iter ffffffff814fc8b0 t ntfs_file_write_iter This can be source of troubles when you create a PMU kprobe for such a function, as it will only install one for the first address (e.g. 0xffffffff814ce3d0 in the above). This could lead to some troubles were BPF based tools does not report any event because the second function is not called: root@vm-amd64:/mnt# mount | grep /mnt /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) # ig is a tool which installs a PMU kprobe on ntfs_file_write_iter(). root@vm-amd64:/mnt# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & [1] 207 root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 3+0 records in 3+0 records out 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00543323 s, 283 kB/s root@vm-amd64:/mnt# fg ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo ^Croot@vm-amd64:/mnt# more /tmp/foo RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM T BYTES OFFSET LAT FILE 214 dd R 512 0 766 foo 214 dd R 512 512 9 foo 214 dd As you can see in the above, only read events are reported and no write because the kprobe is installed for the old ntfs_file_write_iter() and not the ntfs3 one. The same behavior occurs with sysfs kprobe: root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > /sys/kernel/tracing/kprobe_events root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events p:probe/ntfs_file_write_iter ntfs_file_write_iter root@vm-amd64:/# mount | grep /mnt /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) root@vm-amd64:/# perf record -e probe:ntfs_file_write_iter & [1] 210 root@vm-amd64:/# cd /mnt/ root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 3+0 records in 3+0 records out 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00234793 s, 654 kB/s root@vm-amd64:/mnt# cd - / root@vm-amd64:/# fg perf record -e probe:ntfs_file_write_iter ^C[ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.056 MB perf.data ] root@vm-amd64:/# perf report Error: The perf.data data has no samples! # To display the perf.data header info, please use --header/--header-only optio> # In this contribution, I modified the functions creating sysfs and PMU kprobes to test if the function name given as argument matches several symbols. In this case, these functions return EADDRNOTAVAIL to indicate the user to use addr and offs to remove this ambiguity. So, when the above BPF tool is run, the following error message is printed: root@vm-amd64:~# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & [1] 228 root@vm-amd64:~# more /tmp/foo RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM T BYTES OFFSET LAT FILE Error: running gadget: running gadget: installing tracer: attaching kprobe: crea ting perf_kprobe PMU (arch-specific fallback for "ntfs_file_write_iter"): token ntfs_file_write_iter: opening perf event: cannot assign requested address And the same with sysfs kprobe: root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > /sys/kernel/tracing/kprobe_events -bash: echo: write error: Cannot assign requested address Note that, this does not influence perf as it installs kprobes as offset on _text: root@vm-amd64:/# perf probe --add ntfs_file_write_iter Added new events: probe:ntfs_file_write_iter (on ntfs_file_write_iter) probe:ntfs_file_write_iter (on ntfs_file_write_iter) ... root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events p:probe/ntfs_file_write_iter _text+5039088 p:probe/ntfs_file_write_iter _text+5228752 Note that, this contribution is the conclusion of a previous RFC which intended to install a PMU kprobe for all matching symbols [1, 2]. If you see any way to improve this contribution, please share your feedback. Changes since: v1: * Use EADDRNOTAVAIL instead of adding a new error code. * Correct also this behavior for sysfs kprobe. v2: * Count the number of symbols corresponding to function name and return EADDRNOTAVAIL if higher than 1. * Return ENOENT if above count is 0, as it would be returned later by while registering the kprobe. v3: * Check symbol does not contain ':' before testing its uniqueness. * Add a selftest to check this is not possible to install a kprobe for a non unique symbol. v5: * No changes, just add linux-stable as recipient. v6: * Rephrase commit message. * Add "Cc:" to stable. Francis Laniel (2): tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols selftests/ftrace: Add new test case which checks non unique symbol kernel/trace/trace_kprobe.c | 63 +++++++++++++++++++ kernel/trace/trace_probe.h | 1 + .../test.d/kprobe/kprobe_non_uniq_symbol.tc | 13 ++++ 3 files changed, 77 insertions(+) create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc Best regards and thank you in advance. --- [1]: https://lore.kernel.org/lkml/20230816163517.112518-1-flaniel@linux.microsoft.com/ [2]: https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kernel.org/ -- 2.34.1