Subject: Re: [RFC PATCH v1 1/1] Add support for arm64 to carry ima measurement log in kexec_file_load

From: Mimi Zohar <[email-masked]>
Date: Wed, 18 Sep 2019 10:15:11 -0400

Hi Prahkar,

On Fri, 2019-09-13 at 15:50 -0700, Prakhar Srivastava wrote:
> During kexec_file_load, carrying forward the ima measurement log allows
> a verifying party to get the entire runtime event log since the last
> full reboot since that is when PCRs were last reset.
> 
> Signed-off-by: Prakhar Srivastava <[email-masked]>

Missing is the Changelog between versions.  (v1 has now been posted 3
times.)

There's a number of trailing whitespaces, blanks before tabs, and
other warnings.  Please use scripts/checkpatch.pl before posting
patches.

> ---
>  arch/arm64/Kconfig                     |   7 +
>  arch/arm64/include/asm/ima.h           |  29 ++++
>  arch/arm64/include/asm/kexec.h         |   5 +
>  arch/arm64/kernel/Makefile             |   3 +-
>  arch/arm64/kernel/ima_kexec.c          | 213 +++++++++++++++++++++++++
>  arch/arm64/kernel/machine_kexec_file.c |   6 +
>  6 files changed, 262 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/ima.h
>  create mode 100644 arch/arm64/kernel/ima_kexec.c
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 3adcec05b1f6..f39b12dbf9e8 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -976,6 +976,13 @@ config KEXEC_VERIFY_SIG
>  	  verification for the corresponding kernel image type being
>  	  loaded in order for this to work.
>  
> +config HAVE_IMA_KEXEC
> +	bool "Carry over IMA measurement log during kexec_file_load() syscall"
> +	depends on KEXEC_FILE
> +	help
> +	  Select this option to carry over IMA measurement log during
> +	  kexec_file_load.
> +
>  config KEXEC_IMAGE_VERIFY_SIG
>  	bool "Enable Image signature verification support"
>  	default y
> diff --git a/arch/arm64/include/asm/ima.h b/arch/arm64/include/asm/ima.h
> new file mode 100644
> index 000000000000..e23cee84729f
> --- /dev/null
> +++ b/arch/arm64/include/asm/ima.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_ARM64_IMA_H
> +#define _ASM_ARM64_IMA_H
> +
> +struct kimage;
> +
> +int ima_get_kexec_buffer(void **addr, size_t *size);
> +int ima_free_kexec_buffer(void);
> +
> +#ifdef CONFIG_IMA
> +void remove_ima_buffer(void *fdt, int chosen_node);
> +#else
> +static inline void remove_ima_buffer(void *fdt, int chosen_node) {}
> +#endif
> +
> +#ifdef CONFIG_IMA_KEXEC
> +int arch_ima_add_kexec_buffer(struct kimage *image, unsigned long load_addr,
> +			      size_t size);
> +
> +int setup_ima_buffer(const struct kimage *image, void *fdt, int chosen_node);
> +#else
> +static inline int setup_ima_buffer(const struct kimage *image, void *fdt,
> +				   int chosen_node)
> +{
> +	remove_ima_buffer(fdt, chosen_node);
> +	return 0;
> +}
> +#endif /* CONFIG_IMA_KEXEC */
> +#endif /* _ASM_ARM64_IMA_H */
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 12a561a54128..e8d2412066e7 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -96,6 +96,11 @@ static inline void crash_post_resume(void) {}
>  struct kimage_arch {
>  	void *dtb;
>  	unsigned long dtb_mem;
> +
> +#ifdef CONFIG_IMA_KEXEC
> +	phys_addr_t ima_buffer_addr;
> +	size_t ima_buffer_size;
> +#endif
>  };
>  
>  extern const struct kexec_file_ops kexec_image_ops;
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 478491f07b4f..580238f2e9a7 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -55,7 +55,8 @@ obj-$(CONFIG_RANDOMIZE_BASE)		+= kaslr.o
>  obj-$(CONFIG_HIBERNATION)		+= hibernate.o hibernate-asm.o
>  obj-$(CONFIG_KEXEC_CORE)		+= machine_kexec.o relocate_kernel.o	\
>  					   cpu-reset.o
> -obj-$(CONFIG_KEXEC_FILE)		+= machine_kexec_file.o kexec_image.o
> +obj-$(CONFIG_KEXEC_FILE)		+= machine_kexec_file.o kexec_image.o	\
> +					   ima_kexec.o

The kernel may be built with/without IMA enabled or without IMA_KEXEC
support.  Here you're requiring both IMA and IMA_KEXEC to be
configured.  Please refer to the powerpc example.

>  obj-$(CONFIG_ARM64_RELOC_TEST)		+= arm64-reloc-test.o
>  arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
>  obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
> diff --git a/arch/arm64/kernel/ima_kexec.c b/arch/arm64/kernel/ima_kexec.c
> new file mode 100644
> index 000000000000..b14326d541f3
> --- /dev/null
> +++ b/arch/arm64/kernel/ima_kexec.c
> @@ -0,0 +1,213 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Microsoft Corporation.
> + *
> + * Authors:
> + * Prakhar Srivastava <[email-masked]>
> + */
> +
> +#include <linux/slab.h>
> +#include <linux/kexec.h>
> +#include <linux/of.h>
> +#include <linux/memblock.h>
> +#include <linux/libfdt.h>
> +
> +

Extraneous blank line.

> +/**
> + * delete_fdt_mem_rsv - delete memory reservation with given address and size
> + * @fdt - pointer to the fdt.
> + * @start - start address of the memory.
> + * @size - number of cells to be deletd.
> + * 
> + * Return: 0 on success, or negative errno on error.
> + */
> +int delete_fdt_mem_rsv(void *fdt, unsigned long start, unsigned long size)
> +{
> +	int i, ret, num_rsvs = fdt_num_mem_rsv(fdt);
> +
> +	for (i = 0; i < num_rsvs; i++) {
> +		uint64_t rsv_start, rsv_size;
> +
> +		ret = fdt_get_mem_rsv(fdt, i, &rsv_start, &rsv_size);
> +		if (ret) {
> +			pr_err("Malformed device tree\n");
> +			return -EINVAL;
> +		}
> +
> +		if (rsv_start == start && rsv_size == size) {
> +			ret = fdt_del_mem_rsv(fdt, i);
> +			if (ret) {
> +				pr_err("Error deleting device tree reservation\n");
> +				return -EINVAL;
> +			}
> +
> +			return 0;
> +		}
> +	}
> +
> +	return -ENOENT;
> +}
> +
> +/**
> + * remove_ima_buffer - remove the IMA buffer property and reservation
> + * @fdt - pointer the fdt.
> + * @chosen_node - node under which property can be found.
> + * 
> + * The IMA measurement buffer is either read by now and freeed or a kexec call
> + * needs to replace the ima measurement buffer, clear the property and memory
> + * reservation.
> + */
> +void remove_ima_buffer(void *fdt, int chosen_node)
> +{
> +	int ret, len;
> +	const void *prop;
> +	uint64_t tmp_start, tmp_end;
> +
> +	prop = fdt_getprop(fdt, chosen_node, "linux,ima-kexec-buffer", &len);
> +	if (prop) {
> +		tmp_start = fdt64_to_cpu(*((const fdt64_t *) prop));
> +
> +		prop = fdt_getprop(fdt, chosen_node,
> +				   "linux,ima-kexec-buffer-end", &len);
> +		if (!prop)
> +			return;
> +
> +		tmp_end = fdt64_to_cpu(*((const fdt64_t *) prop));
> +
> +		ret = delete_fdt_mem_rsv(fdt, tmp_start, tmp_end - tmp_start);
> +
> +		if (ret == 0)
> +			pr_debug("Removed old IMA buffer reservation.\n");
> +		else if (ret != -ENOENT)
> +			return;
> +
> +		fdt_delprop(fdt, chosen_node, "linux,ima-kexec-buffer");
> +		fdt_delprop(fdt, chosen_node, "linux,ima-kexec-buffer-end");
> +	}
> +}
> +
> +/**
> + * ima_get_kexec_buffer - get IMA buffer from the previous kernel
> + * @addr:	On successful return, set to point to the buffer contents.
> + * @size:	On successful return, set to the buffer size.
> + *
> + * Return: 0 on success, negative errno on error.
> + */
> +int ima_get_kexec_buffer(void **addr, size_t *size)
> +{
> +	int len;
> +	const void *prop;
> +	uint64_t tmp_start, tmp_end;
> +
> +	prop = of_get_property(of_chosen, "linux,ima-kexec-buffer", &len);
> +	if (!prop)
> +		return -ENOENT;
> +
> +	tmp_start = fdt64_to_cpu(*((const fdt64_t *) prop));
> +
> +	prop = of_get_property(of_chosen, "linux,ima-kexec-buffer-end", &len);
> +	if (!prop)
> +		return -ENOENT;
> +
> +	tmp_end = fdt64_to_cpu(*((const fdt64_t *) prop));
> +
> +	*addr = __va(tmp_start);
> +	*size = tmp_end - tmp_start;
> +
> +	return 0;
> +}
> +
> +/**
> + * ima_free_kexec_buffer - free memory used by the IMA buffer
> + *
> + * Return: 0 on success, negative errno on error.
> + */
> +int ima_free_kexec_buffer(void)
> +{
> +	int ret;
> +	void *propStart, *propEnd;

Is there a reason for using mixed case variables?  Why does the
variable need to be prefixed with "prop"?  Wouldn't ima_start/_stop,
 buffer_start/_stop, or even buf_start/_stop be fine?

> +	uint64_t tmp_start, tmp_end;
> +
> +	propStart = of_find_property(of_chosen, "linux,ima-kexec-buffer",
> +				     NULL);
> +	if (propStart) {
> +		tmp_start = fdt64_to_cpu(*((const fdt64_t *) propStart));
> +		ret = of_remove_property(of_chosen, propStart);
> +		if (!ret) {
> +			return ret;
> +		}
> +
> +		propEnd = of_find_property(of_chosen,
> +					   "linux,ima-kexec-buffer-end", NULL);
> +		if (!propEnd) {
> +			return -EINVAL;
> +		}
> +
> +		tmp_end = fdt64_to_cpu(*((const fdt64_t *) propEnd));
> +
> +		ret = of_remove_property(of_chosen, propEnd);
> +		if (!ret) {
> +			return ret;
> +		}

There seems to be quite a bit of code duplication in this function and
in ima_get_kexec_buffer().  It could probably be cleaned up with some
refactoring.

Mimi

> +
> +		return memblock_free(tmp_start, tmp_end - tmp_start);
> +	}
> +	return 0;
> +}
> +
> +#ifdef CONFIG_IMA_KEXEC
> +/**
> + * arch_ima_add_kexec_buffer - do arch-specific steps to add the IMA
> + * 	measurement log.
> + * @image: - pointer to the kimage, to store the address and size of the 
> + *	 IMA measurement log.
> + * @load_addr: - the address where the IMA measurement log is stored.
> + * @size - size of the IMA measurement log.
> + * 
> + * Return: 0 on success, negative errno on error.
> + */
> +int arch_ima_add_kexec_buffer(struct kimage *image, unsigned long load_addr,
> +			      size_t size)
> +{
> +	image->arch.ima_buffer_addr = load_addr;
> +	image->arch.ima_buffer_size = size;
> +	return 0;
> +}
> +
> +/**
> + * setup_ima_buffer - update the fdt to contain the ima mesasurement log
> + * @image: - pointer to the kimage, containing the address and size of
> + *	     the IMA measurement log.
> + * @fdt: - pointer to the fdt.
> + * @chosen_node: - node under which property is to be defined.
> + *  
> + * Return: 0 on success, negative errno on error.
> + */
> +int setup_ima_buffer(const struct kimage *image, void *fdt, int chosen_node)
> +{
> +	int ret;
> +
> +	remove_ima_buffer(fdt, chosen_node);
> +
> +	if (!image->arch.ima_buffer_size)
> +		return 0;
> +
> +	ret = fdt_setprop_u64(fdt, chosen_node, "linux,ima-kexec-buffer",
> +			      image->arch.ima_buffer_addr);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = fdt_setprop_u64(fdt, chosen_node, "linux,ima-kexec-buffer-end",
> +			      image->arch.ima_buffer_addr +
> +			      image->arch.ima_buffer_size);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = fdt_add_mem_rsv(fdt, image->arch.ima_buffer_addr,
> +			      image->arch.ima_buffer_size);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +#endif /* CONFIG_IMA_KEXEC */
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 58871333737a..de5452539c67 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -21,6 +21,7 @@
>  #include <linux/types.h>
>  #include <linux/vmalloc.h>
>  #include <asm/byteorder.h>
> +#include <asm/ima.h>
>  
>  /* relevant device tree properties */
>  #define FDT_PROP_INITRD_START	"linux,initrd-start"
> @@ -85,6 +86,11 @@ static int setup_dtb(struct kimage *image,
>  			goto out;
>  	}
>  
> +	/* add ima measuremnet log buffer */
> +	ret = setup_ima_buffer(image, dtb, off);
> +	if (ret)
> +		goto out;
> +
>  	/* add kaslr-seed */
>  	ret = fdt_delprop(dtb, off, FDT_PROP_KASLR_SEED);
>  	if  (ret == -FDT_ERR_NOTFOUND)

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