On Mon, 19 Aug 2019 at 16:22, Lubashev, Igor <iluba...@akamai.com> wrote: > > On Mon, August 19, 2019 at 12:51 PM Mathieu Poirier > <mathieu.poir...@linaro.org> wrote: > > On Thu, 15 Aug 2019 at 15:42, Arnaldo Carvalho de Melo > > <arnaldo.m...@gmail.com> wrote: > > > > > > Em Thu, Aug 15, 2019 at 02:16:48PM -0600, Mathieu Poirier escreveu: > > > > On Wed, 14 Aug 2019 at 14:02, Lubashev, Igor <iluba...@akamai.com> > > wrote: > > > > > > > > > > > On Wed, August 14, 2019 at 2:52 PM Arnaldo Carvalho de Melo > > <arnaldo.m...@gmail.com> wrote: > > > > > > Em Wed, Aug 14, 2019 at 03:48:14PM -0300, Arnaldo Carvalho de > > > > > > Melo > > > > > > escreveu: > > > > > > > Em Wed, Aug 14, 2019 at 12:04:33PM -0600, Mathieu Poirier > > escreveu: > > > > > > > > # echo 0 > /proc/sys/kernel/kptr_restrict # > > > > > > > > ./tools/perf/perf record -e instructions:k uname > > > > > > > > perf: Segmentation fault > > > > > > > > Obtained 10 stack frames. > > > > > > > > ./tools/perf/perf(sighandler_dump_stack+0x44) > > > > > > > > [0x55af9e5da5d4] > > > > > > > > /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20) [0x7fd31efb6f20] > > > > > > > > ./tools/perf/perf(perf_event__synthesize_kernel_mmap+0xa7) > > > > > > > > [0x55af9e590337] > > > > > > > > ./tools/perf/perf(+0x1cf5be) [0x55af9e50c5be] > > > > > > > > ./tools/perf/perf(cmd_record+0x1022) [0x55af9e50dff2] > > > > > > > > ./tools/perf/perf(+0x23f98d) [0x55af9e57c98d] > > > > > > > > ./tools/perf/perf(+0x23fc9e) [0x55af9e57cc9e] > > > > > > > > ./tools/perf/perf(main+0x369) [0x55af9e4f6bc9] > > > > > > > > /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) > > > > > > > > [0x7fd31ef99b97] > > > > > > > > ./tools/perf/perf(_start+0x2a) [0x55af9e4f704a] Segmentation > > > > > > > > fault > > > > > > > > > > > > > > > > I can reproduce this on both x86 and ARM64. > > > > > > > > > > > > > > I don't see this with these two csets removed: > > > > > > > > > > > > > > 7ff5b5911144 perf symbols: Use CAP_SYSLOG with kptr_restrict > > > > > > > checks d7604b66102e perf tools: Use CAP_SYS_ADMIN with > > > > > > > perf_event_paranoid checks > > > > > > > > > > > > > > Which were the ones I guessed were related to the problem you > > > > > > > reported, so they are out of my ongoing perf/core pull request > > > > > > > to Ingo/Thomas, now trying with these applied and your > > instructions... > > > > > > > > > > > > Can't repro: > > > > > > > > > > > > [root@quaco ~]# cat /proc/sys/kernel/kptr_restrict > > > > > > 0 > > > > > > [root@quaco ~]# perf record -e instructions:k uname Linux [ perf > > record: > > > > > > Woken up 1 times to write data ] [ perf record: Captured and > > > > > > wrote 0.024 MB perf.data (1 samples) ] [root@quaco ~]# echo 1 > > > > > > > /proc/sys/kernel/kptr_restrict [root@quaco ~]# perf record -e > > > > > > instructions:k uname Linux [ perf record: Woken up 1 times to write > > data ] [ perf record: > > > > > > Captured and wrote 0.024 MB perf.data (1 samples) ] [root@quaco > > > > > > ~]# echo > > > > > > 0 > /proc/sys/kernel/kptr_restrict [root@quaco ~]# perf record > > > > > > -e instructions:k uname Linux [ perf record: Woken up 1 times to > > > > > > write data ] [ perf record: Captured and wrote 0.024 MB > > > > > > perf.data (1 samples) ] [root@quaco ~]# > > > > > > > > > > > > [acme@quaco perf]$ git log --oneline --author Lubashev tools/ > > > > > > 7ff5b5911144 (HEAD -> perf/cap, acme.korg/tmp.perf/cap, > > > > > > acme.korg/perf/cap) perf symbols: Use CAP_SYSLOG with > > > > > > kptr_restrict checks d7604b66102e perf tools: Use CAP_SYS_ADMIN > > > > > > with perf_event_paranoid checks c766f3df635d perf ftrace: Use > > > > > > CAP_SYS_ADMIN instead of euid==0 c22e150e3afa perf tools: Add > > > > > > helpers to use capabilities if present > > > > > > 74d5f3d06f70 tools build: Add capability-related feature > > > > > > detection perf version 5.3.rc4.g7ff5b5911144 [acme@quaco perf]$ > > > > > > > > > > I got an ARM64 cloud VM, but I cannot reproduce. > > > > > # cat /proc/sys/kernel/kptr_restrict > > > > > 0 > > > > > > > > > > Perf trace works fine (does not die): > > > > > # ./perf trace -a > > > > > > > > > > Here is my setup: > > > > > Repo: git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git > > > > > Branch: tmp.perf/cap > > > > > Commit: 7ff5b5911 "perf symbols: Use CAP_SYSLOG with kptr_restrict > > checks" > > > > > gcc --version: gcc (Ubuntu/Linaro 7.4.0-1ubuntu1~18.04.1) 7.4.0 > > > > > uname -a: Linux arm-4-par-1 4.9.93-mainline-rev1 #1 SMP Tue Apr 10 > > > > > 09:54:46 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux lsb_release > > > > > -a: Ubuntu 18.04.3 LTS > > > > > > > > > > Auto-detecting system features: > > > > > ... dwarf: [ on ] > > > > > ... dwarf_getlocations: [ on ] > > > > > ... glibc: [ on ] > > > > > ... gtk2: [ on ] > > > > > ... libaudit: [ on ] > > > > > ... libbfd: [ on ] > > > > > ... libcap: [ on ] > > > > > ... libelf: [ on ] > > > > > ... libnuma: [ on ] > > > > > ... numa_num_possible_cpus: [ on ] > > > > > ... libperl: [ on ] > > > > > ... libpython: [ on ] > > > > > ... libcrypto: [ on ] > > > > > ... libunwind: [ on ] > > > > > ... libdw-dwarf-unwind: [ on ] > > > > > ... zlib: [ on ] > > > > > ... lzma: [ on ] > > > > > ... get_cpuid: [ OFF ] > > > > > ... bpf: [ on ] > > > > > ... libaio: [ on ] > > > > > ... libzstd: [ on ] > > > > > ... disassembler-four-args: [ on ] > > > > > > > > > > I also could not reproduce on x86: > > > > > lsb_release -a: Ubuntu 18.04.1 LTS gcc --version: gcc (Ubuntu > > > > > 7.4.0-1ubuntu1~18.04aka10.0.0) 7.4.0 uname -r: 4.4.0-154-generic > > > > > > > > I isolated the problem to libcap-dev - if it is not installed a > > > > segmentation fault will occur. Since this set is about using > > > > capabilities it is obvious that not having it on a system should > > > > fail a trace session, but it should not crash it. > > > > > > It shouldn't crash on x86_64: > > > > > > root@quaco ~]# sysctl kernel.kptr_restrict kernel.kptr_restrict = 0 > > > [root@quaco ~]# perf record -e instructions:k uname Linux [ perf > > > record: Woken up 1 times to write data ] [ perf record: Captured and > > > wrote 0.023 MB perf.data (5 samples) ] [root@quaco ~]# ldd ~/bin/perf > > > | grep libcap [root@quaco ~]# perf -v perf version > > > 5.3.rc4.g329ca330bf8b [root@quaco ~]# [acme@quaco perf]$ git log > > > --oneline -4 329ca330bf8b (HEAD -> perf/cap) perf symbols: Use > > > CAP_SYSLOG with kptr_restrict checks f7b9999387af perf tools: Use > > > CAP_SYS_ADMIN with perf_event_paranoid checks > > > 4d0489cf1c47 (acme.korg/tmp.perf/script-switch-on-off, perf/core) perf > > > report: Add --switch-on/--switch-off events > > > 2f53ae347f59 perf top: Add --switch-on/--switch-off events [acme@quaco > > > perf]$ > > > > > > > If libcap-dev is not installed function > > > > symbol__restricted_filename() will return true, which in turn will > > > > prevent symbol_name to be set in > > > > machine__get_running_kernel_start(). That prevents function > > > > map__set_kallsyms_ref_reloc_sym() from being called in > > > > machine__create_kernel_maps(), resulting in kmap->ref_reloc_sym > > > > being NULL in _perf_event__synthesize_kernel_mmap() and a > > > > segmentation fault. > > > > > > Can you please try with my perf/cap branch? Perhaps you're using > > > Igor's original set of patches? I made changes to the fallback, he was > > > making it return false while I made it fallback to geteuid() == 0, as > > > was before his patches. > > > > Things are working properly on your perf/cap branch. I tested with on both > > x86 and ARM. > > Mathieu, you are probably testing with euid==0.
Very true > If you were to test with euid!=0 but with CAP_SYSLOG and no libcap (and > kptr_restrict=0, perf_event_paranoid=2), you would likely hit the bug that > you identified in __perf_event__synthesize_kermel_mmap(). > > See > https://lkml.kernel.org/lkml/930a59730c0d495f8c5acf4f99048...@usma1ex-dag1mb6.msg.corp.akamai.com > for the fix (Option 1 only or Options 1+2). > > Arnaldo, once we decide what the right fix is, I am happy to post the update > (options 1, 1+2) as a patch series. CC me on the next patchset and I'll be happy to test it. > > - Igor > > > > > > I am not sure how this can be fixed. I counted a total of 19 > > > > instances where kmap->ref_reloc_sym->XYZ is called, only 2 of wich > > > > care to check if kmap->ref_reloc_sym is valid before proceeding. As > > > > such I must hope that in the 17 other cases, kmap->ref_reloc_sym is > > > > guaranteed to be valid. If I am correct then all we need is to > > > > check for a valid pointer in _perf_event__synthesize_kernel_mmap(). > > > > Otherwise it will be a little harder. > > > > > > > > Mathieu >
