Linux-EFI Archive on lore.kernel.org
 help / color / Atom feed
From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Matthew Garrett <mjg59@google.com>,
	Matthew Garrett <matthewgarrett@google.com>
Subject: [PATCH 17/20] efi: Allow disabling PCI busmastering on bridges during boot
Date: Fri,  3 Jan 2020 12:39:50 +0100
Message-ID: <20200103113953.9571-18-ardb@kernel.org> (raw)
In-Reply-To: <20200103113953.9571-1-ardb@kernel.org>

From: Matthew Garrett <matthewgarrett@google.com>

Add an option to disable the busmaster bit in the control register on
all PCI bridges before calling 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 "efi=disable_early_pci_dma"
is passed on the command line, the EFI stub will clear the busmaster bit
on all PCI bridges before ExitBootServices() is called. This will
prevent any malicious PCI devices from being able to perform DMA until
the kernel reenables busmastering after configuring the IOMMU.

This option may cause failures with some poorly behaved hardware and
should not be enabled without testing. The kernel commandline options
"efi=disable_early_pci_dma" or "efi=no_disable_early_pci_dma" may be
used to override the default. Note that PCI devices downstream from PCI
bridges are disconnected from their drivers first, using the UEFI
driver model API, so that DMA can be disabled safely at the bridge
level.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Co-developed-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
[ardb: disconnect PCI I/O handles first, as suggested by Arvind]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |   7 +-
 arch/x86/include/asm/efi.h                    |   5 +
 drivers/firmware/efi/Kconfig                  |  22 ++++
 drivers/firmware/efi/libstub/Makefile         |   2 +-
 .../firmware/efi/libstub/efi-stub-helper.c    |  15 +++
 drivers/firmware/efi/libstub/pci.c            | 114 ++++++++++++++++++
 include/linux/efi.h                           |   6 +-
 7 files changed, 168 insertions(+), 3 deletions(-)
 create mode 100644 drivers/firmware/efi/libstub/pci.c

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ade4e6ec23e0..994632ae48de 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1165,7 +1165,8 @@
 
 	efi=		[EFI]
 			Format: { "old_map", "nochunk", "noruntime", "debug",
-				  "nosoftreserve" }
+				  "nosoftreserve", "disable_early_pci_dma",
+				  "no_disable_early_pci_dma" }
 			old_map [X86-64]: switch to the old ioremap-based EFI
 			runtime services mapping. 32-bit still uses this one by
 			default.
@@ -1180,6 +1181,10 @@
 			claim. Specify efi=nosoftreserve to disable this
 			reservation and treat the memory by its base type
 			(i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
+			disable_early_pci_dma: Disable the busmaster bit on all
+			PCI bridges while in the EFI boot stub
+			no_disable_early_pci_dma: Leave the busmaster bit set
+			on all PCI bridges while in the EFI boot stub
 
 	efi_no_storage_paranoia [EFI; X86]
 			Using this parameter you can use more than 50% of
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 166f0386719e..383f7a0fc170 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -283,6 +283,11 @@ static inline void *efi64_zero_upper(void *p)
 #define __efi64_argmap_locate_protocol(protocol, reg, interface)	\
 	((protocol), (reg), efi64_zero_upper(interface))
 
+/* PCI I/O */
+#define __efi64_argmap_get_location(protocol, seg, bus, dev, func)	\
+	((protocol), efi64_zero_upper(seg), efi64_zero_upper(bus),	\
+	 efi64_zero_upper(dev), efi64_zero_upper(func))
+
 /*
  * The macros below handle the plumbing for the argument mapping. To add a
  * mapping for a specific EFI method, simply define a macro
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index bcc378c19ebe..ecc83e2f032c 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -215,6 +215,28 @@ config EFI_RCI2_TABLE
 
 	  Say Y here for Dell EMC PowerEdge systems.
 
+config EFI_DISABLE_PCI_DMA
+       bool "Clear Busmaster bit on PCI bridges during ExitBootServices()"
+       help
+	  Disable the busmaster bit in the control register on all PCI bridges
+	  while calling 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 you say Y here, the EFI stub will clear the busmaster bit on all
+	  PCI bridges before ExitBootServices() is called. This will prevent
+	  any malicious PCI devices from being able to perform DMA until the
+	  kernel reenables busmastering after configuring the IOMMU.
+
+	  This option will cause failures with some poorly behaved hardware
+	  and should not be enabled without testing. The kernel commandline
+	  options "efi=disable_early_pci_dma" or "efi=no_disable_early_pci_dma"
+	  may be used to override this option.
+
 endmenu
 
 config UEFI_CPER
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index c35f893897e1..98a81576213d 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -39,7 +39,7 @@ OBJECT_FILES_NON_STANDARD	:= y
 KCOV_INSTRUMENT			:= n
 
 lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
-				   random.o
+				   random.o pci.o
 
 # include the stub's generic dependencies from lib/ when building for ARM/arm64
 arm-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index fcc45ee94e02..74ddfb496140 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -33,6 +33,8 @@ static bool __efistub_global efi_nokaslr;
 static bool __efistub_global efi_quiet;
 static bool __efistub_global efi_novamap;
 static bool __efistub_global efi_nosoftreserve;
+static bool __efistub_global efi_disable_pci_dma =
+					IS_ENABLED(CONFIG_EFI_DISABLE_PCI_DMA);
 
 bool __pure nokaslr(void)
 {
@@ -490,6 +492,16 @@ efi_status_t efi_parse_options(char const *cmdline)
 			efi_nosoftreserve = true;
 		}
 
+		if (!strncmp(str, "disable_early_pci_dma", 21)) {
+			str += strlen("disable_early_pci_dma");
+			efi_disable_pci_dma = true;
+		}
+
+		if (!strncmp(str, "no_disable_early_pci_dma", 24)) {
+			str += strlen("no_disable_early_pci_dma");
+			efi_disable_pci_dma = false;
+		}
+
 		/* Group words together, delimited by "," */
 		while (*str && *str != ' ' && *str != ',')
 			str++;
@@ -876,6 +888,9 @@ efi_status_t efi_exit_boot_services(void *handle,
 	if (status != EFI_SUCCESS)
 		goto free_map;
 
+	if (efi_disable_pci_dma)
+		efi_pci_disable_bridge_busmaster();
+
 	status = efi_bs_call(exit_boot_services, handle, *map->key_ptr);
 
 	if (status == EFI_INVALID_PARAMETER) {
diff --git a/drivers/firmware/efi/libstub/pci.c b/drivers/firmware/efi/libstub/pci.c
new file mode 100644
index 000000000000..b025e59b94df
--- /dev/null
+++ b/drivers/firmware/efi/libstub/pci.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI-related functions used by the EFI stub on multiple
+ * architectures.
+ *
+ * Copyright 2019 Google, LLC
+ */
+
+#include <linux/efi.h>
+#include <linux/pci.h>
+
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+void efi_pci_disable_bridge_busmaster(void)
+{
+	efi_guid_t pci_proto = EFI_PCI_IO_PROTOCOL_GUID;
+	unsigned long pci_handle_size = 0;
+	efi_handle_t *pci_handle = NULL;
+	efi_handle_t handle;
+	efi_status_t status;
+	u16 class, command;
+	int i;
+
+	status = efi_bs_call(locate_handle, EFI_LOCATE_BY_PROTOCOL, &pci_proto,
+			     NULL, &pci_handle_size, NULL);
+
+	if (status != EFI_BUFFER_TOO_SMALL) {
+		if (status != EFI_SUCCESS && status != EFI_NOT_FOUND)
+			pr_efi_err("Failed to locate PCI I/O handles'\n");
+		return;
+	}
+
+	status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, pci_handle_size,
+			     (void **)&pci_handle);
+	if (status != EFI_SUCCESS) {
+		pr_efi_err("Failed to allocate memory for 'pci_handle'\n");
+		return;
+	}
+
+	status = efi_bs_call(locate_handle, EFI_LOCATE_BY_PROTOCOL, &pci_proto,
+			     NULL, &pci_handle_size, pci_handle);
+	if (status != EFI_SUCCESS) {
+		pr_efi_err("Failed to locate PCI I/O handles'\n");
+		goto free_handle;
+	}
+
+	for_each_efi_handle(handle, pci_handle, pci_handle_size, i) {
+		efi_pci_io_protocol_t *pci;
+		unsigned long segment_nr, bus_nr, device_nr, func_nr;
+
+		status = efi_bs_call(handle_protocol, handle, &pci_proto,
+				     (void **)&pci);
+		if (status != EFI_SUCCESS)
+			continue;
+
+		/*
+		 * Disregard devices living on bus 0 - these are not behind a
+		 * bridge so no point in disconnecting them from their drivers.
+		 */
+		status = efi_call_proto(pci, get_location, &segment_nr, &bus_nr,
+					&device_nr, &func_nr);
+		if (status != EFI_SUCCESS || bus_nr == 0)
+			continue;
+
+		/*
+		 * Don't disconnect VGA controllers so we don't risk losing
+		 * access to the framebuffer. Drivers for true PCIe graphics
+		 * controllers that are behind a PCIe root port do not use
+		 * DMA to implement the GOP framebuffer anyway [although they
+		 * may use it in their implentation of Gop->Blt()], and so
+		 * disabling DMA in the PCI bridge should not interfere with
+		 * normal operation of the device.
+		 */
+		status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
+					PCI_CLASS_DEVICE, 1, &class);
+		if (status != EFI_SUCCESS || class == PCI_CLASS_DISPLAY_VGA)
+			continue;
+
+		/* Disconnect this handle from all its drivers */
+		efi_bs_call(disconnect_controller, handle, NULL, NULL);
+	}
+
+	for_each_efi_handle(handle, pci_handle, pci_handle_size, i) {
+		efi_pci_io_protocol_t *pci;
+
+		status = efi_bs_call(handle_protocol, handle, &pci_proto,
+				     (void **)&pci);
+		if (status != EFI_SUCCESS || !pci)
+			continue;
+
+		status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
+					PCI_CLASS_DEVICE, 1, &class);
+
+		if (status != EFI_SUCCESS || class != PCI_CLASS_BRIDGE_PCI)
+			continue;
+
+		/* Disable busmastering */
+		status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
+					PCI_COMMAND, 1, &command);
+		if (status != EFI_SUCCESS || !(command & PCI_COMMAND_MASTER))
+			continue;
+
+		command &= ~PCI_COMMAND_MASTER;
+		status = efi_call_proto(pci, pci.write, EfiPciIoWidthUint16,
+					PCI_COMMAND, 1, &command);
+		if (status != EFI_SUCCESS)
+			pr_efi_err("Failed to disable PCI busmastering\n");
+	}
+
+free_handle:
+	efi_bs_call(free_pool, pci_handle);
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index ee68ea6f85ff..7e8e25b1d11c 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -319,7 +319,9 @@ typedef union {
 		void *stall;
 		void *set_watchdog_timer;
 		void *connect_controller;
-		void *disconnect_controller;
+		efi_status_t (__efiapi *disconnect_controller)(efi_handle_t,
+							       efi_handle_t,
+							       efi_handle_t);
 		void *open_protocol;
 		void *close_protocol;
 		void *open_protocol_information;
@@ -1692,4 +1694,6 @@ struct linux_efi_memreserve {
 #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
 	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
 
+void efi_pci_disable_bridge_busmaster(void);
+
 #endif /* _LINUX_EFI_H */
-- 
2.20.1


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-03 11:39 [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 01/20] efi/libstub: fix boot argument handling in mixed mode entry code Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 03/20] efi/x86: re-disable RT services for 32-bit kernels running on 64-bit EFI Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 04/20] efi/x86: map the entire EFI vendor string before copying it Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 05/20] efi/x86: avoid redundant cast of EFI firmware service pointer Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 06/20] efi/x86: split off some old memmap handling into separate routines Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 07/20] efi/x86: split SetVirtualAddresMap() wrappers into 32 and 64 bit versions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 08/20] efi/x86: simplify i386 efi_call_phys() firmware call wrapper Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 09/20] efi/x86: simplify 64-bit EFI " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 10/20] efi/x86: simplify mixed mode " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 11/20] efi/x86: drop two near identical versions of efi_runtime_init() Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 12/20] efi/x86: clean up efi_systab_init() routine for legibility Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 13/20] efi/x86: don't panic or BUG() on non-critical error conditions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 14/20] efi/x86: remove unreachable code in kexec_enter_virtual_mode() Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 15/20] efi/x86: Check number of arguments to variadic functions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 16/20] efi/x86: Allow translating 64-bit arguments for mixed mode calls Ard Biesheuvel
2020-01-03 11:39 ` Ard Biesheuvel [this message]
2020-01-03 11:39 ` [PATCH 18/20] x86/mm: fix NX bit clearing issue in kernel_map_pages_in_pgd Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 19/20] efi/x86: don't map the entire kernel text RW for mixed mode Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 20/20] efi/x86: avoid RWX mappings for all of DRAM Ard Biesheuvel
2020-01-09  9:37 ` [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-10 18:13   ` Ingo Molnar
2020-01-13  7:29     ` Ard Biesheuvel

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200103113953.9571-18-ardb@kernel.org \
    --to=ardb@kernel.org \
    --cc=ard.biesheuvel@linaro.org \
    --cc=linux-efi@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=matthewgarrett@google.com \
    --cc=mingo@kernel.org \
    --cc=mjg59@google.com \
    --cc=nivedita@alum.mit.edu \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-EFI Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-efi/0 linux-efi/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-efi linux-efi/ https://lore.kernel.org/linux-efi \
		linux-efi@vger.kernel.org
	public-inbox-index linux-efi

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-efi


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git