Re: [PATCH v2 1/3] efi: Add device path parser

[Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Wed, Oct 19, 2016 at 12:17:28PM +0100, Matt Fleming wrote:
> (Cc'ing Peter since he's played with device path parsing before)

So the only two thoughts I have:

1) I think we should probably be a bit more aggressive about bounds
   checking.  Every once in a while there are implementations that build
   device paths from templates and occasionally leave
   efi_dev_path.length as 0 or 0xffff, or forget to put an End Entire
   Device Path node at the end (or put an End Device Path Instance in
   instead.)  So checking for ->length < PAGE_SIZE and that when a dp
   node crosses a page boundary, the new page is actually in the same map
   as the previous one wouldn't be a terrible idea.
2) I think we should decide how multiple-instance device path are going
   to work sooner rather than later, mostly because I have a use for them
   and it seems harder to graft them in later.  My first idea here is to
   make get_device_by_efi_path() return 0 for "stop iterating" and 1 for
   "there's more device paths later", and then make it merely set *dev =
   NULL when we just don't /support/ the device path we found, rather than
   returning error.  Either case would still set *node to the (possibly
   inexistent) next node.  If we did that, we could easily rename it
   get_devices_by_path() and make get_device_by_path() a special case
   with exactly the semantics we have now.

> 
> On Mon, 17 Oct, at 12:57:23PM, Lukas Wunner wrote:
> > We're about to extended the efistub to retrieve device properties from
> > EFI on Apple Macs. The properties use EFI Device Paths to indicate the
> > device they belong to. This commit adds a parser which, given an EFI
> > Device Path, locates the corresponding struct device and returns a
> > reference to it.
> > 
> > Initially only ACPI and PCI Device Path nodes are supported, these are
> > the only types needed for Apple device properties (the corresponding
> > macOS function AppleACPIPlatformExpert::matchEFIDevicePath() does not
> > support any others). Further node types can be added with moderate
> > effort.
> > 
> > Apple device properties is currently the only use case of this parser,
> > but since this may be useful to others, make it a separate component
> > which can be selected with config option EFI_DEV_PATH_PARSER. It can
> > in principle be compiled as a module if acpi_get_first_physical_node()
> > and acpi_bus_type are exported (and get_device_by_efi_path() itself is
> > exported).
> > 
> > The dependency on CONFIG_ACPI is needed for acpi_match_device_ids().
> > It can be removed if an empty inline stub is added for that function.
> > 
> > Cc: Matt Fleming <matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>
> > Cc: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> > Signed-off-by: Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
> > ---
> >  drivers/firmware/efi/Kconfig           |   5 +
> >  drivers/firmware/efi/Makefile          |   1 +
> >  drivers/firmware/efi/dev-path-parser.c | 186 +++++++++++++++++++++++++++++++++
> >  include/linux/efi.h                    |  21 ++++
> >  4 files changed, 213 insertions(+)
> >  create mode 100644 drivers/firmware/efi/dev-path-parser.c
> > 
> > diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> > index c981be1..893fda4 100644
> > --- a/drivers/firmware/efi/Kconfig
> > +++ b/drivers/firmware/efi/Kconfig
> > @@ -133,3 +133,8 @@ endmenu
> >  
> >  config UEFI_CPER
> >  	bool
> > +
> > +config EFI_DEV_PATH_PARSER
> > +	bool
> > +	depends on ACPI
> > +	default n
> > diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> > index c8a439f..3e91ae3 100644
> > --- a/drivers/firmware/efi/Makefile
> > +++ b/drivers/firmware/efi/Makefile
> > @@ -21,6 +21,7 @@ obj-$(CONFIG_EFI_STUB)			+= libstub/
> >  obj-$(CONFIG_EFI_FAKE_MEMMAP)		+= fake_mem.o
> >  obj-$(CONFIG_EFI_BOOTLOADER_CONTROL)	+= efibc.o
> >  obj-$(CONFIG_EFI_TEST)			+= test/
> > +obj-$(CONFIG_EFI_DEV_PATH_PARSER)	+= dev-path-parser.o
> >  
> >  arm-obj-$(CONFIG_EFI)			:= arm-init.o arm-runtime.o
> >  obj-$(CONFIG_ARM)			+= $(arm-obj-y)
> > diff --git a/drivers/firmware/efi/dev-path-parser.c b/drivers/firmware/efi/dev-path-parser.c
> > new file mode 100644
> > index 0000000..549f80b
> > --- /dev/null
> > +++ b/drivers/firmware/efi/dev-path-parser.c
> > @@ -0,0 +1,186 @@
> > +/*
> > + * dev-path-parser.c - EFI Device Path parser
> > + * Copyright (C) 2016 Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License (version 2) as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/efi.h>
> > +#include <linux/pci.h>
> > +
> > +struct acpi_hid_uid {
> > +	struct acpi_device_id hid[2];
> > +	char uid[11]; /* UINT_MAX + null byte */
> > +};
> > +
> > +static int __init acpi_match(struct device *dev, void *data)
> > +{
> > +	struct acpi_hid_uid hid_uid = *(struct acpi_hid_uid *)data;
> > +	struct acpi_device *adev = to_acpi_device(dev);
> > +
> > +	if (acpi_match_device_ids(adev, hid_uid.hid))
> > +		return 0;
> > +
> > +	if (adev->pnp.unique_id)
> > +		return !strcmp(adev->pnp.unique_id, hid_uid.uid);
> > +	else
> > +		return !strcmp("0", hid_uid.uid);
> > +}
> > +
> > +static int __init get_device_by_acpi_path(struct efi_dev_path *node,
> > +					  struct device *parent,
> > +					  struct device **child)
> > +{
> > +	struct acpi_hid_uid hid_uid = {};
> > +	struct device *phys_dev;
> > +
> > +	if (node->length != 12)
> > +		return -EINVAL;
> > +
> > +	sprintf(hid_uid.hid[0].id, "%c%c%c%04X",
> > +		'A' + ((node->acpi.hid >> 10) & 0x1f) - 1,
> > +		'A' + ((node->acpi.hid >>  5) & 0x1f) - 1,
> > +		'A' + ((node->acpi.hid >>  0) & 0x1f) - 1,
> > +			node->acpi.hid >> 16);
> > +	sprintf(hid_uid.uid, "%u", node->acpi.uid);
> > +
> > +	*child = bus_find_device(&acpi_bus_type, NULL, &hid_uid, acpi_match);
> > +	if (!*child)
> > +		return -ENODEV;
> > +
> > +	phys_dev = acpi_get_first_physical_node(to_acpi_device(*child));
> > +	if (phys_dev) {
> > +		get_device(phys_dev);
> > +		put_device(*child);
> > +		*child = phys_dev;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int __init pci_match(struct device *dev, void *data)
> > +{
> > +	unsigned int devfn = *(unsigned int *)data;
> > +
> > +	return dev_is_pci(dev) && to_pci_dev(dev)->devfn == devfn;
> > +}
> > +
> > +static int __init get_device_by_pci_path(struct efi_dev_path *node,
> > +					 struct device *parent,
> > +					 struct device **child)
> > +{
> > +	unsigned int devfn;
> > +
> > +	if (node->length != 6)
> > +		return -EINVAL;
> > +	if (!parent)
> > +		return -EINVAL;
> > +
> > +	devfn = PCI_DEVFN(node->pci.dev, node->pci.fn);
> > +
> > +	*child = device_find_child(parent, &devfn, pci_match);
> > +	if (!*child)
> > +		return -ENODEV;
> > +
> > +	return 0;
> > +}
> > +
> > +/*
> > + * Insert parsers for further node types here.
> > + *
> > + * Each parser takes a pointer to the @node and to the @parent (will be NULL
> > + * for the first device path node). If a device corresponding to @node was
> > + * found below @parent, its reference count should be incremented and the
> > + * device returned in @child.
> > + *
> > + * The return value should be 0 on success or a negative int on failure.
> > + * The special return value 1 signals the end of the device path, only
> > + * get_device_by_end_path() is supposed to return this.
> > + *
> > + * Be sure to validate the node length and contents before commencing the
> > + * search for a device.
> > + */
> > +
> > +static int __init get_device_by_end_path(struct efi_dev_path *node,
> > +					 struct device *parent,
> > +					 struct device **child)
> > +{
> > +	if (node->length != 4)
> > +		return -EINVAL;
> > +	if (!parent)
> > +		return -ENODEV;
> > +
> > +	*child = get_device(parent);
> > +	return 1;
> > +}
> > +
> > +/**
> > + * get_device_by_efi_path - find device by EFI Device Path
> > + * @node: EFI Device Path
> > + * @len: maximum length of EFI Device Path in bytes
> > + * @dev: device found
> > + *
> > + * Parse a series of EFI Device Path nodes at @node and find the corresponding
> > + * device. If the device was found, its reference count is incremented and a
> > + * pointer to it is returned in @dev. The caller needs to drop the reference
> > + * with put_device() after use. The @node pointer is updated to point to the
> > + * location immediately after the "End Entire Device Path" node.
> > + *
> > + * If a Device Path node is malformed or its corresponding device is not found,
> > + * @node is updated to point to this offending node and @dev will be %NULL.
> > + *
> > + * Most buses instantiate devices in "subsys" initcall level, hence the
> > + * earliest initcall level in which this function should be called is "fs".
> > + *
> > + * Returns 0 on success,
> > + *	   %-ENODEV if no device was found,
> > + *	   %-EINVAL if a node is malformed or exceeds @len,
> > + *	   %-ENOTSUPP if support for a node type is not yet implemented.
> > + */
> > +int __init get_device_by_efi_path(struct efi_dev_path **node, size_t len,
> > +				  struct device **dev)
> > +{
> > +	struct device *parent = NULL, *child;
> > +	int ret = 0;
> > +
> > +	*dev = NULL;
> > +
> > +	while (ret != 1) {
> > +		if (len < 4 || len < (*node)->length)
> > +			ret = -EINVAL;
> > +		else if ((*node)->type     == EFI_DEV_ACPI &&
> > +			 (*node)->sub_type == EFI_DEV_BASIC_ACPI)
> > +			ret = get_device_by_acpi_path(*node, parent, &child);
> > +		else if ((*node)->type     == EFI_DEV_HW &&
> > +			 (*node)->sub_type == EFI_DEV_PCI)
> > +			ret = get_device_by_pci_path(*node, parent, &child);
> > +		else if (((*node)->type    == EFI_DEV_END_PATH ||
> > +			  (*node)->type    == EFI_DEV_END_PATH2) &&
> > +			 (*node)->sub_type == EFI_DEV_END_ENTIRE)
> > +			ret = get_device_by_end_path(*node, parent, &child);
> > +		else
> > +			ret = -ENOTSUPP;
> > +
> > +		put_device(parent);
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		parent = child;
> > +		*node  = (void *)*node + (*node)->length;
> > +		len   -= (*node)->length;
> > +	}
> > +
> > +	*dev = child;
> > +	return 0;
> > +}
> 
> Where in your patch series is this function called? Am I missing
> something?
> 
> Also, unless there's some existing namespace with "get_device_by_*"
> I'd prefer for this function name to have "efi_" as the prefix.
> 
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index 2d08948..4faf339 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -1145,6 +1145,27 @@ struct efi_generic_dev_path {
> >  	u16 length;
> >  } __attribute ((packed));
> >  
> > +struct efi_dev_path {
> > +	u8 type;	/* can be replaced with unnamed */
> > +	u8 sub_type;	/* struct efi_generic_dev_path; */
> > +	u16 length;	/* once we've moved to -std=c11 */
> > +	union {
> > +		struct {
> > +			u32 hid;
> > +			u32 uid;
> > +		} acpi;
> > +		struct {
> > +			u8 fn;
> > +			u8 dev;
> > +		} pci;
> > +	};
> > +} __attribute ((packed));
> > +
> > +#if IS_ENABLED(CONFIG_EFI_DEV_PATH_PARSER)
> > +int get_device_by_efi_path(struct efi_dev_path **node, size_t len,
> > +			   struct device **dev);
> > +#endif
> > +
> >  static inline void memrange_efi_to_native(u64 *addr, u64 *npages)
> >  {
> >  	*npages = PFN_UP(*addr + (*npages<<EFI_PAGE_SHIFT)) - PFN_DOWN(*addr);
> > -- 
> > 2.9.3
> > 

-- 
        Peter