RE: [PATCH v3 3/4] perf: Use CAP_SYSLOG with kptr_restrict checks

[Lubashev, Igor]

> On Wed, August 14, 2019 at 2:52 PM Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> 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