linux-kernel - Re: [PATCH] selftest/x86/meltdown: Add a selftest for meltdown

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Date:   Thu, 5 Jan 2023 11:11:15 -0300
From:   "Raphael S. Carvalho" <raphaelsc@...lladb.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Aaron Lu <aaron.lu@...el.com>, Dave Hansen <dave.hansen@...el.com>,
        Pavel Boldin <pboldin@...udlinux.com>,
        Pavel Boldin <boldin.pavel@...il.com>,
        Moritz Lipp <github@....me>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Michael Schwarz <michael.schwarz91@...il.com>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftest/x86/meltdown: Add a selftest for meltdown

On Thu, Jan 5, 2023 at 10:42 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Jan 05, 2023 at 08:35:05PM +0800, Aaron Lu wrote:
> > To capture potential programming errors like mistakenly setting Global
> > bit on kernel page table entries, a selftest for meltdown is added.
> >
> > This selftest is based on Pavel Boldin's work at:
> > https://github.com/linux-test-project/ltp/blob/master/testcases/cve/meltdown.c
> >
> > In addition to the existing test of reading kernel variable
> > saved_command_line from user space, one more test of reading user local
> > variable through kernel direct map address is added. For the existing
> > test(reading saved_command_line) to report a failure, both the high kernel
> > mapping and low kernel mapping have to be in leaked state; For the added
> > test(read local var), only low kernel mapping leak is enough to trigger
> > a test fail, so both tests are useful.
> >
> > Test results of 10 runs:
> >
> > On v6.1-rc8 with nopti kernel cmdline option:
> >
> > host              test_out_rate_1    test_out_rate_2
> > lkp-bdw-de1            50%               100%
> > lkp-hsw-d01            70%               100%
> > lkp-hsw-d02             0%                80%
> > lkp-hsw-d03            60%               100%
> > lkp-hsw-d04            20%               100%
> > lkp-hsw-d05            60%               100%
> > lkp-ivb-d01             0%                70%
> > lkp-kbl-d01           100%               100%
> > lkp-skl-d02           100%                90%
> > lkp-skl-d03            90%               100%
> > lkp-skl-d05            60%               100%
> > kbl-vm                100%                80%
> > 2 other machines have 0% rate for both tests.
> >
> > bdw=broadwell, hsw=haswell, ivb=ivybridge, etc.
> >
> > test_out_rate_1: test reports fail rate for the test of reading
> > saved_command_line from user space;
> > test_out_rate_2: test reports fail rate for the test of reading user
> > local variable through kernel direct map address in user space.
> >
> > On v5.19 without nopti cmdline option:
> > host              test_out_rate_2
> > lkp-bdw-de1            80%
> > lkp-hsw-4ex1           50%
> > lkp-hsw-d01            30%
> > lkp-hsw-d03            10%
> > lkp-hsw-d04            10%
> > lkp-kbl-d01            10%
> > kbl-vm                 80%
> > 7 other machines have 0% rate for test2.
> >
> > Also tested on an i386 VM with 512M memory and the test out rate is 100%
> > when adding nopti to kernel cmdline with v6.1-rc8.
> >
> > Main changes I made from Pavel Boldin's meltdown test are:
> > - Replace rdtscll() and clflush() with kernel's implementation;
> > - Reimplement find_symbol_in_file() to avoid bringing in LTP's library
> >   functions;
> > - Coding style changes: placing the function return type in the same
> >   line of the function.
> >
> > Signed-off-by: Aaron Lu <aaron.lu@...el.com>
> > ---
> > Notable changes from RFC v3:
> > - Drop RFC tag;
> > - Change the base code from zlib licensed one to GPL licensed one.
>
> Sorry, but this still gets my NAK for the issues raised in previous
> reviews that are not addressed here for some reason :(

Greg, the selftest is no longer based on
https://github.com/IAIK/meltdown/blob/master/LICENSE, which is
originally zlib licensed. In this version, Aaron is basing the test on
https://github.com/linux-test-project/ltp/blob/master/testcases/cve/meltdown.c,
which is indeed licensed with: GPL-2.0-or-later

>
> greg k-h