linux-kernel - Re: [RFD] x86: The future of MPX

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Date:   Sat, 28 Apr 2018 19:50:43 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [RFD] x86: The future of MPX


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Sat, Apr 28, 2018 at 2:18 AM Ingo Molnar <mingo@...nel.org> wrote:
> 
> > I just tried the MPX testcases with the latest kernel:
> 
> >   deimos:~/tip/tools/testing/selftests/x86> ./mpx-mini-test_64
> 
> They need to be run as root. They try to access
> 
>      /sys/kernel/debug/tracing/set_ftrace_pid
>      /sys/kernel/debug/tracing/trace
> 
> and that's root-only.

Indeed - but note that they are crashing as root as well here:

  root@...mos:/home/mingo/tip/tools/testing/selftests/x86# ./mpx-mini-test_64 
  [...]
  Aborted (core dumped)

... because I don't even have /sys/kernel/debug/tracing/set_ftrace_pid... :-/

That's despite having ftrace enabled.

After some digging I found out that 'set_ftrace_pid' is dependent on 
CONFIG_FUNCTION_TRACING=y (not just CONFIG_TRACING=y), which I didn't
have enabled on this kernel.

After enabling it I got the 64-bit testcase to work:

  #
  ...
  ./mpx-mini-test_64 completed successfully

But the 32-bit testcase is erroring out:

  root@...mos:/home/mingo/tip/tools/testing/selftests/x86# ./mpx-mini-test_32 
  XSAVE is supported by HW & OS
  XSAVE processor supported state mask: 0x21f
  XSAVE OS supported state mask: 0x21f
   BNDREGS: size: 64 user: 1 supervisor: 0 aligned: 0
    BNDCSR: size: 64 user: 1 supervisor: 0 aligned: 0
  executing unmaptest
  mpx dig (  1) complete, SUCCESS (       0 /    0)
  #BR status == 2, missing bounds table,kernel should have handled!!

v4.17-rc2 based kernel, so it should have the latest MPX code.

Thanks,

	Ingo