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Date:   Sun, 17 Oct 2021 18:17:04 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     "Reshetova, Elena" <elena.reshetova@intel.com>
Cc:     Andi Kleen <ak@linux.intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        "Lutomirski, Andy" <luto@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Richard Henderson <rth@twiddle.net>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        James E J Bottomley <James.Bottomley@hansenpartnership.com>,
        Helge Deller <deller@gmx.de>,
        "David S . Miller" <davem@davemloft.net>,
        Arnd Bergmann <arnd@arndb.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Paolo Bonzini <pbonzini@redhat.com>,
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        Peter H Anvin <hpa@zytor.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
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Subject: Re: [PATCH v5 12/16] PCI: Add pci_iomap_host_shared(),
 pci_iomap_host_shared_range()
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On Thu, Oct 14, 2021 at 12:33:49PM +0000, Reshetova, Elena wrote:
> > On Thu, Oct 14, 2021 at 07:27:42AM +0000, Reshetova, Elena wrote:
> > > > On Thu, Oct 14, 2021 at 06:32:32AM +0000, Reshetova, Elena wrote:
> > > > > > On Tue, Oct 12, 2021 at 06:36:16PM +0000, Reshetova, Elena wrote:
> > > > > > > > The 5.15 tree has something like ~2.4k IO accesses (including MMIO and
> > > > > > > > others) in init functions that also register drivers (thanks Elena for
> > > > > > > > the number)
> > > > > > >
> > > > > > > To provide more numbers on this. What I can see so far from a smatch-
> > based
> > > > > > > analysis, we have 409 __init style functions (.probe & builtin/module_
> > > > > > > _platform_driver_probe excluded) for 5.15 with allyesconfig.
> > > > > >
> > > > > > I don't think we care about allyesconfig at all though.
> > > > > > Just don't do that.
> > > > > > How about allmodconfig? This is closer to what distros actually do.
> > > > >
> > > > > It does not make any difference really for the content of the /drivers/*:
> > > > > gives 408 __init style functions doing IO (.probe & builtin/module_
> > > > > > > _platform_driver_probe excluded) for 5.15 with allmodconfig:
> > > > >
> > > > > ['doc200x_ident_chip',
> > > > > 'doc_probe', 'doc2001_init', 'mtd_speedtest_init',
> > > > > 'mtd_nandbiterrs_init', 'mtd_oobtest_init', 'mtd_pagetest_init',
> > > > > 'tort_init', 'mtd_subpagetest_init', 'fixup_pmc551',
> > > > > 'doc_set_driver_info', 'init_amd76xrom', 'init_l440gx',
> > > > > 'init_sc520cdp', 'init_ichxrom', 'init_ck804xrom', 'init_esb2rom',
> > > > > 'probe_acpi_namespace_devices', 'amd_iommu_init_pci', 'state_next',
> > > > > 'arm_v7s_do_selftests', 'arm_lpae_run_tests', 'init_iommu_one',
> > > >
> > > > Um. ARM? Which architecture is this build for?
> > >
> > > The list of smatch IO findings is built for x86, but the smatch cross function
> > > database covers all archs, so when queried for all potential function callers,
> > > it would show non x86 arch call chains also.
> > >
> > > Here is the original x86 finding and call chain for the 'arm_v7s_do_selftests':
> > >
> > >   Detected low-level IO from arm_v7s_do_selftests in fun
> > > __iommu_queue_command_sync
> > >
> > > drivers/iommu/amd/iommu.c:1025 __iommu_queue_command_sync() error:
> > > {15002074744551330002}
> > >     'check_host_input' read from the host using function 'readl' to a
> > > member of the structure 'iommu->cmd_buf_head';
> > >
> > > __iommu_queue_command_sync()
> > >   iommu_completion_wait()
> > >     amd_iommu_domain_flush_complete()
> > >       iommu_v1_map_page()
> > >         arm_v7s_do_selftests()
> > >
> > > So, the results can be further filtered if you want a specified arch.
> > 
> > So what is it just for x86? Could you tell?
> 
> I can probably figure out how to do additional filtering here, but does
> it really matter for the case that is being discussed here? Andi's point was
> that there quite many existing places in the kernel when low-level IO
> happens before the probe stage. So I brought these numbers here.
> What do you plan to do with the pure x86 results? 

If the list is short - just suggest securing that ;)


> And here are the full results for allyesconfig, if anyone is interested (just got permission to create
> the repository today):
> https://github.com/intel/ccc-linux-guest-hardening/tree/master/audit/sample_output/5.15-rc1
> We will be pushing to this repo all the scripts and fuzzing setups we use as part of
> our Linux guest hardening effort for confidential cloud computing, but it is going to take
> some time to get all the approvals collected.  
> 
> Best Regards,
> Elena.