Re: [PATCH 5.5 000/176] 5.5.8-stable review

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Mar 04, 2020 at 09:47:02AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Mar 04, 2020 at 09:11:28AM +0100, Greg Kroah-Hartman wrote:
> > On Wed, Mar 04, 2020 at 12:43:42PM +0530, Naresh Kamboju wrote:
> > > On Tue, 3 Mar 2020 at 23:16, Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > This is the start of the stable review cycle for the 5.5.8 release.
> > > > There are 176 patches in this series, all will be posted as a response
> > > > to this one.  If anyone has any issues with these being applied, please
> > > > let me know.
> > > >
> > > > Responses should be made by Thu, 05 Mar 2020 17:42:06 +0000.
> > > > Anything received after that time might be too late.
> > > >
> > > > The whole patch series can be found in one patch at:
> > > >         https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/patch-5.5.8-rc1.gz
> > > > or in the git tree and branch at:
> > > >         git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.5.y
> > > > and the diffstat can be found below.
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > > >
> > > 
> > > Results from Linaro’s test farm.
> > > Regressions detected on x86_64 and i386.
> > > 
> > > Test failure output:
> > > CVE-2017-5715: VULN (IBRS+IBPB or retpoline+IBPB+RSB filling, is
> > > needed to mitigate the vulnerability)
> > > 
> > > Test description:
> > > CVE-2017-5715 branch target injection (Spectre Variant 2)
> > > 
> > > Impact: Kernel
> > > Mitigation 1: new opcode via microcode update that should be used by
> > > up to date compilers to protect the BTB (by flushing indirect branch
> > > predictors)
> > > Mitigation 2: introducing "retpoline" into compilers, and recompile
> > > software/OS with it
> > > Performance impact of the mitigation: high for mitigation 1, medium
> > > for mitigation 2, depending on your CPU
> > 
> > So these are regressions or just new tests?
> > 
> > If regressions, can you do 'git bisect' to find the offending commit?
> > 
> > Also, are you sure you have an updated microcode on these machines and a
> > proper compiler for retpoline?
> 
> As an example of just how crazy that script is, here's the output of my
> machine for that first CVE issue:
> 
> CVE-2017-5715 aka 'Spectre Variant 2, branch target injection'
> * Mitigated according to the /sys interface:  YES  (Mitigation: Full generic retpoline, IBPB: conditional, IBRS_FW, STIBP: conditional, RSB filling)
> * Mitigation 1
>   * Kernel is compiled with IBRS support:  YES
>     * IBRS enabled and active:  YES  (for firmware code only)
>   * Kernel is compiled with IBPB support:  YES
>     * IBPB enabled and active:  YES
> * Mitigation 2
>   * Kernel has branch predictor hardening (arm):  NO
>   * Kernel compiled with retpoline option:  YES
>     * Kernel compiled with a retpoline-aware compiler:  YES  (kernel reports full retpoline compilation)
>   * Kernel supports RSB filling:  UNKNOWN  (couldn't check (couldn't find your kernel image in /boot, if you used netboot, this is normal))
> > STATUS:  VULNERABLE  (IBRS+IBPB or retpoline+IBPB+RSB filling, is needed to mitigate
> 
> So why is this "Vulnerable"?  Because it didn't think it could find my
> kernel image for some odd reason, despite it really being in /boot/ (I
> don't use netboot)
> 
> So please verify that this really is a real issue, and not just the
> script doing foolish things.

And, if I tell the script where my kernel image is, suddenly all is
good:

CVE-2017-5715 aka 'Spectre Variant 2, branch target injection'
* Mitigation 1
  * Kernel is compiled with IBRS support:  YES
    * IBRS enabled and active:  N/A  (not testable in offline mode)
  * Kernel is compiled with IBPB support:  YES
    * IBPB enabled and active:  N/A  (not testable in offline mode)
* Mitigation 2
  * Kernel has branch predictor hardening (arm):  UNKNOWN
  * Kernel compiled with retpoline option:  UNKNOWN  (couldn't read your kernel configuration)
  * Kernel supports RSB filling:  YES
> STATUS:  NOT VULNERABLE  (offline mode: kernel supports IBRS + IBPB to mitigate the vulnerability)