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From: Andy Lutomirski <luto@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi <linux-efi@vger.kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Matthew Garrett <matthewgarrett@google.com>,
	Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Matthew Garrett <mjg59@google.com>
Subject: Re: [PATCH v2 21/21] efi: Allow disabling PCI busmastering on bridges during boot
Date: Wed, 18 Dec 2019 18:50:00 -0800	[thread overview]
Message-ID: <CALCETrWLMeSbmL_ff=AOmuswxWgvRu75cpNPz9SZgeNwex+ygg@mail.gmail.com> (raw)
In-Reply-To: <20191218170139.9468-22-ardb@kernel.org>

On Wed, Dec 18, 2019 at 9:03 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> From: Matthew Garrett <matthewgarrett@google.com>
>
> Add an option to disable the busmaster bit in the control register on
> all PCI bridges during the invocation of ExitBootServices() and passing
> control to the runtime kernel. System firmware may configure the IOMMU
> to prevent malicious PCI devices from being able to attack the OS via DMA.
> However, since firmware can't guarantee that the OS is IOMMU-aware, it
> will tear down IOMMU configuration when ExitBootServices() is called.
> This leaves a window between where a hostile device could still cause
> damage before Linux configures the IOMMU again.
>
> If CONFIG_EFI_DISABLE_PCI_DMA is enabled or the "efi=disable_pci_dma"
> command line argument is passed, the EFI stub will clear the busmaster
> bit on all PCI bridges before ExitBootServices() completes. This will
> prevent any malicious PCI devices from being able to perform DMA until
> the kernel reenables busmastering after configuring the IOMMU.
>
> This option is disabled when in EFI mixed mode environments (ie, 64-bit
> kernels with a 32-bit EFI implementation), given that the use of EFI
> events is not supported in this case.
>
> This option may cause failures with some poorly behaved hardware and
> should not be enabled without testing. The kernel commandline options
> "efi=disable_pci_dma" or "efi=no_disable_pci_dma" may be used to
> override the default.

Could this maybe be efi=disable_early_pci_dma?

As it stands, it reads like busmastering is turned off and stays off,
which is not the case.  I'm dreading the silly forum posts saying
"your system is slow, and busmastering is leet, so use
efi=no_disable_pci_dma to allow busmastering and make it OMG fast".

--Andy

  reply	other threads:[~2019-12-19  2:50 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-18 17:01 [PATCH v2 00/21] efi/x86: confine type unsafe casting to mixed mode Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 01/21] efi/libstub: remove unused __efi_call_early() macro Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 02/21] efi/x86: rename efi_is_native() to efi_is_mixed() Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 03/21] efi/libstub: use a helper to iterate over a EFI handle array Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 04/21] efi/libstub: extend native protocol definitions with mixed_mode aliases Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 05/21] efi/libstub: distinguish between native/mixed not 32/64 bit Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 06/21] efi/libstub/x86: use mixed mode helpers to populate efi_config Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 07/21] efi/libstub: drop explicit 32/64-bit protocol definitions Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 08/21] efi/libstub: use stricter typing for firmware function pointers Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 09/21] efi/libstub: annotate firmware routines as __efiapi Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 10/21] efi/libstub/x86: avoid thunking for native firmware calls Ard Biesheuvel
2019-12-21 21:22   ` Hans de Goede
2019-12-22 12:02     ` Ard Biesheuvel
2019-12-22 12:37       ` Ard Biesheuvel
2019-12-22 12:46       ` Andy Lutomirski
2019-12-22 15:29         ` Ard Biesheuvel
2019-12-22 21:12           ` Arvind Sankar
2019-12-22 21:25             ` Ard Biesheuvel
2019-12-23 11:49       ` Hans de Goede
2019-12-23 12:00         ` Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 11/21] efi/libstub: get rid of 'sys_table_arg' macro parameter Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 12/21] efi/libstub: unify the efi_char16_printk implementations Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 13/21] efi/libstub/x86: drop __efi_early() export of efi_config struct Ard Biesheuvel
2019-12-24 19:34   ` Hans de Goede
2019-12-25 14:42     ` Ard Biesheuvel
2019-12-27 22:44       ` Hans de Goede
2019-12-27 22:51         ` Ard Biesheuvel
2019-12-31 23:04   ` Arvind Sankar
2020-01-01 18:13     ` Ard Biesheuvel
2020-01-01 19:08       ` Arvind Sankar
2020-01-02  7:33         ` Ard Biesheuvel
2020-01-02 14:06           ` Arvind Sankar
2020-01-02 15:20             ` Ard Biesheuvel
2020-01-02 15:51               ` Arvind Sankar
2020-01-02 15:58                 ` Ard Biesheuvel
2020-01-02 16:28                   ` Ard Biesheuvel
2020-01-02 16:59                     ` Ard Biesheuvel
2020-01-02 17:26                       ` Arvind Sankar
2020-01-02 17:30                         ` Ard Biesheuvel
2020-01-02 17:41                           ` Arvind Sankar
2020-01-02 17:48                             ` Ard Biesheuvel
2020-01-02 18:10                               ` Arvind Sankar
2020-01-02 18:38                                 ` Ard Biesheuvel
2020-01-03 14:16                                   ` Arvind Sankar
2020-01-03 14:23                                     ` Ard Biesheuvel
2020-01-02 18:38                               ` Arvind Sankar
2020-01-02 16:59                     ` Arvind Sankar
2020-01-02 17:03                       ` Ard Biesheuvel
2020-01-02 17:21                         ` Arvind Sankar
2019-12-18 17:01 ` [PATCH v2 14/21] efi/libstub: drop sys_table_arg from printk routines Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 15/21] efi/libstub: remove 'sys_table_arg' from all function prototypes Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 16/21] efi/libstub: drop protocol argument from efi_call_proto() macro Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 17/21] efi/libstub: drop 'table' argument from efi_table_attr() macro Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 18/21] efi/libstub: use 'func' not 'f' as macro parameter Ard Biesheuvel
2019-12-31 16:51   ` Arvind Sankar
2019-12-31 17:06     ` Ard Biesheuvel
2019-12-31 17:36       ` Arvind Sankar
2019-12-18 17:01 ` [PATCH v2 19/21] efi/libstub: tidy up types and names of global cmdline variables Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 20/21] efi/libstub: import type definitions for creating and signalling events Ard Biesheuvel
2019-12-18 17:01 ` [PATCH v2 21/21] efi: Allow disabling PCI busmastering on bridges during boot Ard Biesheuvel
2019-12-19  2:50   ` Andy Lutomirski [this message]
2019-12-19 13:17     ` Ard Biesheuvel
2019-12-19 20:04       ` Matthew Garrett
2019-12-19 20:04   ` Matthew Garrett
2019-12-20  7:06     ` Ard Biesheuvel
2019-12-20  7:17       ` Andy Lutomirski
2019-12-20  8:11         ` Ard Biesheuvel
2019-12-20 19:41           ` Arvind Sankar
2020-01-02 14:46             ` Laszlo Ersek
2020-01-02 15:40               ` Ard Biesheuvel
2019-12-20 20:43       ` Matthew Garrett
2019-12-21 16:44         ` Ard Biesheuvel
2019-12-21 21:24           ` Matthew Garrett
2019-12-21 22:54             ` Arvind Sankar
2019-12-23 14:02               ` Ard Biesheuvel
2019-12-23 15:46                 ` Arvind Sankar
2019-12-23 15:58                   ` Ard Biesheuvel
2019-12-23 16:12                     ` Arvind Sankar
2019-12-23 20:57                   ` Matthew Garrett
2020-02-06 14:30   ` Hans de Goede
2020-02-06 14:35     ` Ard Biesheuvel
2020-03-04 10:38       ` Hans de Goede
2020-03-04 18:26         ` Ard Biesheuvel
2020-03-04 18:49           ` Hans de Goede
2020-03-04 21:59             ` Ard Biesheuvel
2019-12-19 11:12 ` [PATCH v2 00/21] efi/x86: confine type unsafe casting to mixed mode Hans de Goede
2019-12-19 13:22   ` Ard Biesheuvel

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