linux-kernel - [RFC 0/3] Put vdso in ramfs-like filesystem (vdsofs)

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Date:   Thu, 25 Aug 2016 18:21:07 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     <linux-kernel@...r.kernel.org>, <mingo@...hat.com>
CC:     <luto@...capital.net>, <tglx@...utronix.de>, <hpa@...or.com>,
        <x86@...nel.org>, <0x7f454c46@...il.com>, <oleg@...hat.com>,
        <rostedt@...dmis.org>, <viro@...iv.linux.org.uk>,
        Dmitry Safonov <dsafonov@...tuozzo.com>
Subject: [RFC 0/3] Put vdso in ramfs-like filesystem (vdsofs)

This patches set is cleanly RFC and is not supposed to be applied.
Also for RFC time it builds only on x86_64.

So, in a mail thread Oleg told that it would be worth to introduce vm_file
for vdso mappings as currently uprobes can not be placed on vDSO VMAs [1].
In this patches set I introduce in-kernel filesystem for vdso files.
After patches vDSO VMA now has inode and is just a private file mapping:
7ffcc4b2b000-7ffcc4b2d000 r--p 00000000 00:00 0                          [vvar]
7ffcc4b2d000-7ffcc4b2f000 r-xp 00000000 00:09 18                         [vdso]

Then I introduce interface in uprobe_events to insert uprobes in vdso.
FWIW:
  [~]# cd kernel/linux
  [linux]# readelf --syms arch/x86/entry/vdso/vdso64.so
Symbol table '.dynsym' contains 11 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 0000000000000470     0 SECTION LOCAL  DEFAULT    8 
     2: 00000000000008d0   885 FUNC    WEAK   DEFAULT   12 clock_gettime@@LINUX_2.6
     3: 0000000000000c50   472 FUNC    GLOBAL DEFAULT   12 __vdso_gettimeofday@@LINUX_2.6
     4: 0000000000000c50   472 FUNC    WEAK   DEFAULT   12 gettimeofday@@LINUX_2.6
     5: 0000000000000e30    21 FUNC    GLOBAL DEFAULT   12 __vdso_time@@LINUX_2.6
     6: 0000000000000e30    21 FUNC    WEAK   DEFAULT   12 time@@LINUX_2.6
     7: 00000000000008d0   885 FUNC    GLOBAL DEFAULT   12 __vdso_clock_gettime@@LINUX_2.6
     8: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LINUX_2.6
     9: 0000000000000e50    41 FUNC    GLOBAL DEFAULT   12 __vdso_getcpu@@LINUX_2.6
    10: 0000000000000e50    41 FUNC    WEAK   DEFAULT   12 getcpu@@LINUX_2.6
  [~]# cd /sys/kernel/debug/tracing/
  [tracing]# echo 'p:clock_gettime :vdso:/64:0x8d0' > uprobe_events
  [tracing]# echo 'p:gettimeofday :vdso:/64:0xc50' >> uprobe_events
  [tracing]# echo 'p:time :vdso:/64:0xe30' >> uprobe_events
  [tracing]# echo 1 > events/uprobes/enable
  [tracing]# su test # it has UID=1001
  [tracing]$ date
  Thu Aug 25 17:19:29 MSK 2016
  [tracing]$ exit
  [tracing]# cat trace
  # tracer: nop
  #
  # entries-in-buffer/entries-written: 175/175   #P:4
  #
  #                              _-----=> irqs-off
  #                             / _----=> need-resched
  #                            | / _---=> hardirq/softirq
  #                            || / _--=> preempt-depth
  #                            ||| /     delay
  #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
  #              | |       |   ||||       |         |
              bash-11560 [001] d...   316.470236: time: (0x7ffcacebae30)
              bash-11560 [001] d...   316.471436: gettimeofday: (0x7ffcacebac50)
              bash-11560 [001] d...   316.477550: time: (0x7ffcacebae30)
              bash-11560 [001] d...   316.477655: time: (0x7ffcacebae30)
            mktemp-11568 [001] d...   316.479589: gettimeofday: (0x7ffc603f0c50)
              date-11571 [001] d...   316.481890: clock_gettime: (0x7ffec9db58d0)
[...]  

If this approach will be decided as fine, I will prepare a better version,
fixing the following things:
o put vdsofs in generic fs/* dir
o support other archs and vdso blobs
o remove BUG_ON()'s and UID==1001 check
o remove extern's and use headers only
o refactor code in create_trace_uprobe()
o add some state to (struct trace_uprobe), so i.e., `cat uprobe_events` will
  print those uprobes as vdso-based
o document this interface in Documentation/trace/uprobetracer.txt
o prepare nice patches set?

So, opinions? Is it worth to add something like this?

[1]: https://lkml.org/lkml/2016/7/12/346

Dmitry Safonov (3):
  x86/vdso: create vdso file, use it for mapping
  uprobe: drop isdigit() check in create_trace_uprobe
  uprobe: add vdso support

Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Dmitry Safonov <0x7f454c46@...il.com>

 arch/x86/entry/vdso/vma.c   | 148 ++++++++++++++++++++++++++++++++++++++++++--
 kernel/trace/trace_uprobe.c |  50 +++++++++++----
 2 files changed, 180 insertions(+), 18 deletions(-)

-- 
2.9.0