[Bug libc/27300] New: GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[Bug libc/27300] New: GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

            Bug ID: 27300
           Summary: GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not
                    working
           Product: glibc
           Version: 2.31
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: honggyu.kp at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Hi,

I'm developing a function tracing tool called
uftrace(https://github.com/namhyung/uftrace) and trying to handle the case when
Intel CET feature is on.

In the project, we've handled this case in the previous issue for Fedora at
https://github.com/namhyung/uftrace/issues/738.

But it started to be broken in ubuntu 20.04. It's may because the CET is on by
default and it adds endbr64 instruction at the entry of each function.

00000000000011c0 <main>:
    11c0:       f3 0f 1e fa             endbr64
    11c4:       55                      push   %rbp
    11c5:       48 89 e5                mov    %rsp,%rbp
            ...

It was handled by setting GLIBC_TUNABLES as follows.

  GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK

But it doesn't work unlike Fedora and we've also tried again with

  GLIBC_TUNABLES=glibc.cpu.x86_ibt=off:glibc.cpu.x86_shstk=off

It doesn't work as well.

I've found two commits related to those but those are not included in
glibc-2.31.
-
https://sourceware.org/git/?p=glibc.git;a=commit;h=94cd37ebb293321115a36a422b091fdb72d2fb08
-
https://sourceware.org/git/?p=glibc.git;a=commit;h=04dff6fc0d4ad44fc4491f89fed6574380b78251

It looks like there can be another bug in glibc in Ubuntu 20.04 and it uses
glibc-2.31.

  $ ls -l /lib/x86_64-linux-gnu/libc.so.6
  lrwxrwxrwx 1 root root 12 Dec 16 11:04 /lib/x86_64-linux-gnu/libc.so.6 ->
libc-2.31.so

Could anyone please have a look if it's another bug?

Otherwise, it'd be helpful if someone can help how I can disable Intel CET
feature at runtime.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

Honggyu Kim <honggyu.kp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com,
                   |                            |honggyu.kp at gmail dot com

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #1 from Honggyu Kim <honggyu.kp at gmail dot com> ---
Hi H.J. Lu,

Could you please have a look at this issue if possible?

Thanks,
Honggyu

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #2 from Honggyu Kim <honggyu.kp at gmail dot com> ---
This problem is discussed in the following issue.
- https://github.com/namhyung/uftrace/issues/1231

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

Honggyu Kim <honggyu.kp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://github.com/namhyung
                   |                            |/uftrace/issues/1231
           Keywords|                            |glibc_2.31

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> ---
Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
branch at:

https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31

have been applied in glibc in Ubuntu 20.04.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2021-01-31

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #4 from Honggyu Kim <honggyu.kp at gmail dot com> ---
(In reply to H.J. Lu from comment #3)
> Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
> branch at:
> 
> https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31
> 
> have been applied in glibc in Ubuntu 20.04.

Thanks for the quick reply. Does it mean that they are not applied in Ubuntu
20.04 so it makes the problem? If so, is there any way to avoid this problem?

I don't have a machine that has Ubuntu 20.10 so will test it after setting it
up. Thanks very much for your help.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|WAITING                     |RESOLVED

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Honggyu Kim from comment #4)
> (In reply to H.J. Lu from comment #3)
> > Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
> > branch at:
> > 
> > https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31
> > 
> > have been applied in glibc in Ubuntu 20.04.
> 
> Thanks for the quick reply. Does it mean that they are not applied in Ubuntu
> 20.04 so it makes the problem? If so, is there any way to avoid this problem?
> 
> I don't have a machine that has Ubuntu 20.10 so will test it after setting
> it up. Thanks very much for your help.

Please disable CET under Ubuntu 20.04 or use Ubuntu 20.10.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #6 from Honggyu Kim <honggyu.kp at gmail dot com> ---
(In reply to H.J. Lu from comment #5)
> (In reply to Honggyu Kim from comment #4)
> > (In reply to H.J. Lu from comment #3)
> > > Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
> > > branch at:
> > > 
> > > https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31
> > > 
> > > have been applied in glibc in Ubuntu 20.04.
> > 
> > Thanks for the quick reply. Does it mean that they are not applied in Ubuntu
> > 20.04 so it makes the problem? If so, is there any way to avoid this problem?
> > 
> > I don't have a machine that has Ubuntu 20.10 so will test it after setting
> > it up. Thanks very much for your help.
> 
> Please disable CET under Ubuntu 20.04

Thanks but how can I disable CET?

> or use Ubuntu 20.10.

The thing is that we want to support uftrace tool to cover all the distros
including Ubuntu 20.04. Our users cannot properly use the specific feature due
to this problem.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Honggyu Kim from comment #6)
> (In reply to H.J. Lu from comment #5)
> > (In reply to Honggyu Kim from comment #4)
> > > (In reply to H.J. Lu from comment #3)
> > > > Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
> > > > branch at:
> > > > 
> > > > https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31
> > > > 
> > > > have been applied in glibc in Ubuntu 20.04.
> > > 
> > > Thanks for the quick reply. Does it mean that they are not applied in Ubuntu
> > > 20.04 so it makes the problem? If so, is there any way to avoid this problem?
> > > 
> > > I don't have a machine that has Ubuntu 20.10 so will test it after setting
> > > it up. Thanks very much for your help.
> > 
> > Please disable CET under Ubuntu 20.04
> 
> Thanks but how can I disable CET?

Usage: elfedit <option(s)> elffile(s)
 Update the ELF header of ELF files
...
  --disable-x86-feature [ibt|shstk|lam_u48|lam_u57]
                              Disable x86 feature
...

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #8 from Honggyu Kim <honggyu.kp at gmail dot com> ---
(In reply to H.J. Lu from comment #7)
> (In reply to Honggyu Kim from comment #6)
> > (In reply to H.J. Lu from comment #5)
> > > (In reply to Honggyu Kim from comment #4)
> > > > (In reply to H.J. Lu from comment #3)
> > > > > Please use Ubuntu 20.10 or verify that all patches on users/hjl/cet/2.31
> > > > > branch at:
> > > > > 
> > > > > https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/2.31
> > > > > 
> > > > > have been applied in glibc in Ubuntu 20.04.
> > > > 
> > > > Thanks for the quick reply. Does it mean that they are not applied in Ubuntu
> > > > 20.04 so it makes the problem? If so, is there any way to avoid this problem?
> > > > 
> > > > I don't have a machine that has Ubuntu 20.10 so will test it after setting
> > > > it up. Thanks very much for your help.
> > > 
> > > Please disable CET under Ubuntu 20.04
> > 
> > Thanks but how can I disable CET?
> 
> Usage: elfedit <option(s)> elffile(s)
>  Update the ELF header of ELF files
> ...
>   --disable-x86-feature [ibt|shstk|lam_u48|lam_u57]
>                               Disable x86 feature
> ...

Hmm.. I can remove the IBT and SHSTK bits from the elf file, but it doesn't
actually fix the problem when GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK works
properly.

I will try to find another way to avoid this problem. Thanks very much for your
help.

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[honggyu.kp at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27300

--- Comment #9 from Honggyu Kim <honggyu.kp at gmail dot com> ---
(In reply to H.J. Lu from comment #3)
> Please use Ubuntu 20.10

This problem happens also in Ubuntu 20.10, which uses libc-2.32.so.

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[Bug libc/27300] GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK not working

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--- Comment #10 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Honggyu Kim from comment #9)
> (In reply to H.J. Lu from comment #3)
> > Please use Ubuntu 20.10
> 
> This problem happens also in Ubuntu 20.10, which uses libc-2.32.so.

$ GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK

on Fedora 33, which also has glibc 2.32, works for me.  Please update
to the last Ubuuntu 20.10.  If it still doesn't work, report it to
Canonical.

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