Re: [PATCH 4/7] efi: Add an EFI signature blob parser

[Mimi Zohar]

On Sun, 2018-11-25 at 20:44 +0530, Nayna Jain wrote:
> From: Dave Howells <dhowells@xxxxxxxxxx>
> 
> Add a function to parse an EFI signature blob looking for elements of
> interest. A list is made up of a series of sublists, where all the
> elements in a sublist are of the same type, but sublists can be of
> different types.
> 
> For each sublist encountered, the function pointed to by the
> get_handler_for_guid argument is called with the type specifier GUID and
> returns either a pointer to a function to handle elements of that type or
> NULL if the type is not of interest.
> 
> If the sublist is of interest, each element is passed to the handler
> function in turn.

There are a few checkpatch.pl warnings that need to be
addressed, including the missing SPDX license.

Mimi

> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
> ---
> Changelog:
> 
> v0:
> - removed the CONFIG EFI_SIGNATURE_LIST_PARSER
> - moved efi_parser.c from certs to security/integrity/platform_certs
>   directory
> 
>  include/linux/efi.h                            |   9 ++
>  security/integrity/Makefile                    |   3 +-
>  security/integrity/platform_certs/efi_parser.c | 112 +++++++++++++++++++++++++
>  3 files changed, 123 insertions(+), 1 deletion(-)
>  create mode 100644 security/integrity/platform_certs/efi_parser.c
> 
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 99cba6fe1234..2016145e2d6d 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1138,6 +1138,15 @@ extern int efi_memattr_apply_permissions(struct mm_struct *mm,
>  char * __init efi_md_typeattr_format(char *buf, size_t size,
>  				     const efi_memory_desc_t *md);
>  
> +
> +typedef void (*efi_element_handler_t)(const char *source,
> +				      const void *element_data,
> +				      size_t element_size);
> +extern int __init parse_efi_signature_list(
> +	const char *source,
> +	const void *data, size_t size,
> +	efi_element_handler_t (*get_handler_for_guid)(const efi_guid_t *));
> +
>  /**
>   * efi_range_is_wc - check the WC bit on an address range
>   * @start: starting kvirt address
> diff --git a/security/integrity/Makefile b/security/integrity/Makefile
> index 046ffc1bb42d..6ee9058866cd 100644
> --- a/security/integrity/Makefile
> +++ b/security/integrity/Makefile
> @@ -9,7 +9,8 @@ integrity-y := iint.o
>  integrity-$(CONFIG_INTEGRITY_AUDIT) += integrity_audit.o
>  integrity-$(CONFIG_INTEGRITY_SIGNATURE) += digsig.o
>  integrity-$(CONFIG_INTEGRITY_ASYMMETRIC_KEYS) += digsig_asymmetric.o
> -integrity-$(CONFIG_INTEGRITY_PLATFORM_KEYRING) += platform_certs/platform_keyring.o
> +integrity-$(CONFIG_INTEGRITY_PLATFORM_KEYRING) += platform_certs/platform_keyring.o \
> +						  platform_certs/efi_parser.o
>  
>  subdir-$(CONFIG_IMA)			+= ima
>  obj-$(CONFIG_IMA)			+= ima/
> diff --git a/security/integrity/platform_certs/efi_parser.c b/security/integrity/platform_certs/efi_parser.c
> new file mode 100644
> index 000000000000..4e396f98f5c7
> --- /dev/null
> +++ b/security/integrity/platform_certs/efi_parser.c
> @@ -0,0 +1,112 @@
> +/* EFI signature/key/certificate list parser
> + *
> + * Copyright (C) 2012, 2016 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@xxxxxxxxxx)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#define pr_fmt(fmt) "EFI: "fmt
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/err.h>
> +#include <linux/efi.h>
> +
> +/**
> + * parse_efi_signature_list - Parse an EFI signature list for certificates
> + * @source: The source of the key
> + * @data: The data blob to parse
> + * @size: The size of the data blob
> + * @get_handler_for_guid: Get the handler func for the sig type (or NULL)
> + *
> + * Parse an EFI signature list looking for elements of interest.  A list is
> + * made up of a series of sublists, where all the elements in a sublist are of
> + * the same type, but sublists can be of different types.
> + *
> + * For each sublist encountered, the @get_handler_for_guid function is called
> + * with the type specifier GUID and returns either a pointer to a function to
> + * handle elements of that type or NULL if the type is not of interest.
> + *
> + * If the sublist is of interest, each element is passed to the handler
> + * function in turn.
> + *
> + * Error EBADMSG is returned if the list doesn't parse correctly and 0 is
> + * returned if the list was parsed correctly.  No error can be returned from
> + * the @get_handler_for_guid function or the element handler function it
> + * returns.
> + */
> +int __init parse_efi_signature_list(
> +	const char *source,
> +	const void *data, size_t size,
> +	efi_element_handler_t (*get_handler_for_guid)(const efi_guid_t *))
> +{
> +	efi_element_handler_t handler;
> +	unsigned offs = 0;
> +
> +	pr_devel("-->%s(,%zu)\n", __func__, size);
> +
> +	while (size > 0) {
> +		const efi_signature_data_t *elem;
> +		efi_signature_list_t list;
> +		size_t lsize, esize, hsize, elsize;
> +
> +		if (size < sizeof(list))
> +			return -EBADMSG;
> +
> +		memcpy(&list, data, sizeof(list));
> +		pr_devel("LIST[%04x] guid=%pUl ls=%x hs=%x ss=%x\n",
> +			 offs,
> +			 list.signature_type.b, list.signature_list_size,
> +			 list.signature_header_size, list.signature_size);
> +
> +		lsize = list.signature_list_size;
> +		hsize = list.signature_header_size;
> +		esize = list.signature_size;
> +		elsize = lsize - sizeof(list) - hsize;
> +
> +		if (lsize > size) {
> +			pr_devel("<--%s() = -EBADMSG [overrun @%x]\n",
> +				 __func__, offs);
> +			return -EBADMSG;
> +		}
> +
> +		if (lsize < sizeof(list) ||
> +		    lsize - sizeof(list) < hsize ||
> +		    esize < sizeof(*elem) ||
> +		    elsize < esize ||
> +		    elsize % esize != 0) {
> +			pr_devel("- bad size combo @%x\n", offs);
> +			return -EBADMSG;
> +		}
> +
> +		handler = get_handler_for_guid(&list.signature_type);
> +		if (!handler) {
> +			data += lsize;
> +			size -= lsize;
> +			offs += lsize;
> +			continue;
> +		}
> +
> +		data += sizeof(list) + hsize;
> +		size -= sizeof(list) + hsize;
> +		offs += sizeof(list) + hsize;
> +
> +		for (; elsize > 0; elsize -= esize) {
> +			elem = data;
> +
> +			pr_devel("ELEM[%04x]\n", offs);
> +			handler(source,
> +				&elem->signature_data,
> +				esize - sizeof(*elem));
> +
> +			data += esize;
> +			size -= esize;
> +			offs += esize;
> +		}
> +	}
> +
> +	return 0;
> +}