Re: [PATCH v4] x86/kexec: Carry forward IMA measurement log on kexec

[Lakshmi Ramasubramanian <nramas@linux.microsoft.com>]

>>> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
>>> index 170d0fd68b1f..54bd4ce5f908 100644
>>> --- a/arch/x86/kernel/kexec-bzimage64.c
>>> +++ b/arch/x86/kernel/kexec-bzimage64.c
>>> @@ -186,6 +186,33 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
>>>    }
>>>    #endif /* CONFIG_EFI */
>>> +static void
>>> +setup_ima_state(const struct kimage *image, struct boot_params *params,
>>> +		unsigned long params_load_addr,
>>> +		unsigned int ima_setup_data_offset)
>>> +{
>>> +#ifdef CONFIG_IMA_KEXEC
>>> +	struct setup_data *sd = (void *)params + ima_setup_data_offset;
>>> +	unsigned long setup_data_phys;
>>> +	struct ima_setup_data *ima;
>>> +
>>> +	if (!image->ima_buffer_size)
>>> +		return;
>>> +
>>> +	sd->type = SETUP_IMA;
>>> +	sd->len = sizeof(*ima);
>>> +
>>> +	ima = (void *)sd + sizeof(struct setup_data);
>>> +	ima->addr = image->ima_buffer_addr;
>>> +	ima->size = image->ima_buffer_size;
>>> +
>>> +	/* Add setup data */
>>> +	setup_data_phys = params_load_addr + ima_setup_data_offset;
>>> +	sd->next = params->hdr.setup_data;
>>> +	params->hdr.setup_data = setup_data_phys;
>>> +#endif /* CONFIG_IMA_KEXEC */
>>> +}
>>> +
>>>    static int
>>>    setup_boot_parameters(struct kimage *image, struct boot_params *params,
>>>    		      unsigned long params_load_addr,
>>> @@ -247,6 +274,13 @@ setup_boot_parameters(struct kimage *image, struct boot_params *params,
>>>    	setup_efi_state(params, params_load_addr, efi_map_offset, efi_map_sz,
>>>    			efi_setup_data_offset);
>>>    #endif
>>> +
>>> +	/* Setup IMA log buffer state */
>>> +	setup_ima_state(image, params, params_load_addr,
>>> +			efi_setup_data_offset +
>>> +			sizeof(struct setup_data) +
>>> +			sizeof(struct efi_setup_data));
>> Here you could check image->ima_buffer_size and call setup_ima_state() only
>> if it is non-zero.
> 
> setup_ima_state() has this check already.

Yes - I noticed that.
I was just suggesting a minor optimization - avoid making this function 
call if IMA buffer is not present.

> 
>>> +
>>>    	/* Setup EDD info */
>>>    	memcpy(params->eddbuf, boot_params.eddbuf,
>>>    				EDDMAXNR * sizeof(struct edd_info));
>>> @@ -403,6 +437,10 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
>>>    				sizeof(struct setup_data) +
>>>    				sizeof(struct efi_setup_data);
>>> +	if (IS_ENABLED(CONFIG_IMA_KEXEC))
>>> +		kbuf.bufsz += sizeof(struct setup_data) +
>>> +			      sizeof(struct ima_setup_data);
>>> +
>>>    	params = kzalloc(kbuf.bufsz, GFP_KERNEL);
>>>    	if (!params)
>>>    		return ERR_PTR(-ENOMEM);
>>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>>> index 249981bf3d8a..ab5e7a351845 100644
>>> --- a/arch/x86/kernel/setup.c
>>> +++ b/arch/x86/kernel/setup.c
>>> @@ -11,6 +11,7 @@
>>>    #include <linux/dma-map-ops.h>
>>>    #include <linux/dmi.h>
>>>    #include <linux/efi.h>
>>> +#include <linux/ima.h>
>>>    #include <linux/init_ohci1394_dma.h>
>>>    #include <linux/initrd.h>
>>>    #include <linux/iscsi_ibft.h>
>>> @@ -145,6 +146,11 @@ __visible unsigned long mmu_cr4_features __ro_after_init;
>>>    __visible unsigned long mmu_cr4_features __ro_after_init = X86_CR4_PAE;
>>>    #endif
>>> +#ifdef CONFIG_IMA
>>> +static phys_addr_t ima_kexec_buffer_phys;
>>> +static size_t ima_kexec_buffer_size;
>>> +#endif
>>> +
>>>    /* Boot loader ID and version as integers, for the benefit of proc_dointvec */
>>>    int bootloader_type, bootloader_version;
>>> @@ -335,6 +341,59 @@ static void __init reserve_initrd(void)
>>>    }
>>>    #endif /* CONFIG_BLK_DEV_INITRD */
>>> +static void __init add_early_ima_buffer(u64 phys_addr)
>>> +{
>>> +#ifdef CONFIG_IMA
>>> +	struct ima_setup_data *data;
>>> +
>>> +	data = early_memremap(phys_addr + sizeof(struct setup_data),
>>> +			      sizeof(*data));
>>> +	if (!data) {
>>> +		pr_warn("setup: failed to memremap ima_setup_data entry\n");
>>> +		return;
>>> +	}
>> Here if memory allocation fails, would kexec system call fail or would it
>> only not add IMA buffer, but continue with the system call?
> 
> This is run in the context of the *new* kernel. Boot will continue, but
> the IMA buffer will not be successfully passed across. Effectively that
> puts us in the same situation as now; things like TPM PCRs will have
> been updated, but we won't have the log showing us how we got to the
> current state.
I think it is better to treat this error as a critical failure.

> 
>>> +	if (data->size != 0) {
>>> +		memblock_reserve(data->addr, data->size);
>>> +		ima_kexec_buffer_phys = data->addr;
>>> +		ima_kexec_buffer_size = data->size;
>>> +	}
>>> +	early_memunmap(data, sizeof(*data));
>>> +#else
>>> +	pr_warn("Passed IMA kexec data, but CONFIG_IMA not set. Ignoring.\n");
>> Is this warning message useful? Can we just inline (NOP) this function if
>> CONFIG_IMA is not set?
> 
> It seems useful to me to know if the previous kernel is trying to pass
> us IMA information but we're not configured for IMA, and it's not a lot
> of overhead in terms of code in a path that's only actually executed if
> we *are* passed the IMA kexec info.

okay.

> 
>>> +#endif
>>> +}
>>> +
>>> +#if defined(CONFIG_IMA) && !defined(CONFIG_OF_FLATTREE)
>>> +int __meminit ima_free_kexec_buffer(void)
>>> +{
>> ima_free_kexec_buffer() should be invoked if the previous kernel had passed
>> the IMA buffer (i.e., CONFIG_HAVE_IMA_KEXEC is set). CONFIG_HAVE_IMA_KEXEC
>> would be set only if CONFIG_IMA is set. Is the above check still required?
> 
> If we don't have IMA configured there's no point compiling this code in,
> as there will be no callers of it. The OF_FLATTREE piece is to handle
> the fact that the x86 platforms that use device tree (see previous
> discussion in this thread about the fact there only seem to be 2 of
> them, and they're both 32 bit) will end up needing to wire up the device
> tree kexec passing if they want to use this functionality (and in fact
> device tree passing across x86 kexec generally).

okay.

  -lakshmi

>>
>>> +	int rc;
>>> +
>>> +	if (ima_kexec_buffer_size == 0)
>>> +		return -ENOENT;
>>> +
>>> +	rc = memblock_phys_free(ima_kexec_buffer_phys,
>>> +				ima_kexec_buffer_size);
>>> +	if (rc)
>>> +		return rc;
>>> +
>>> +	ima_kexec_buffer_phys = 0;
>>> +	ima_kexec_buffer_size = 0;
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +int __init ima_get_kexec_buffer(void **addr, size_t *size)
>>> +{
>>> +	if (ima_kexec_buffer_size == 0)
>>> +		return -ENOENT;
>>> +
>>> +	*addr = __va(ima_kexec_buffer_phys);
>>> +	*size = ima_kexec_buffer_size;
>>> +
>>> +	return 0;
>>> +}
>>> +#endif
>>> +
>>>    static void __init parse_setup_data(void)
>>>    {
>>>    	struct setup_data *data;
>>> @@ -360,6 +419,9 @@ static void __init parse_setup_data(void)
>>>    		case SETUP_EFI:
>>>    			parse_efi_setup(pa_data, data_len);
>>>    			break;
>>> +		case SETUP_IMA:
>>> +			add_early_ima_buffer(pa_data);
>>> +			break;
>>>    		default:
>>>    			break;
>>>    		}
>>> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
>>> index b9bd1cff1793..74fdd490f7c0 100644
>>> --- a/drivers/of/kexec.c
>>> +++ b/drivers/of/kexec.c
>>> @@ -9,6 +9,7 @@
>>>     *  Copyright (C) 2016  IBM Corporation
>>>     */
>>> +#include <linux/ima.h>
>>>    #include <linux/kernel.h>
>>>    #include <linux/kexec.h>
>>>    #include <linux/memblock.h>
>>> diff --git a/include/linux/ima.h b/include/linux/ima.h
>>> index 426b1744215e..ff4bd993e432 100644
>>> --- a/include/linux/ima.h
>>> +++ b/include/linux/ima.h
>>> @@ -140,6 +140,11 @@ static inline int ima_measure_critical_data(const char *event_label,
>>>    #endif /* CONFIG_IMA */
>>> +#ifdef CONFIG_HAVE_IMA_KEXEC
>>> +int ima_free_kexec_buffer(void);
>>> +int ima_get_kexec_buffer(void **addr, size_t *size);
>>> +#endif
>>> +
>>>    #ifdef CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT
>>>    extern bool arch_ima_get_secureboot(void);
>>>    extern const char * const *arch_get_ima_policy(void);
>>> diff --git a/include/linux/of.h b/include/linux/of.h
>>> index 04971e85fbc9..c2f58d2e3a0e 100644
>>> --- a/include/linux/of.h
>>> +++ b/include/linux/of.h
>>> @@ -441,8 +441,6 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
>>>    				   unsigned long initrd_load_addr,
>>>    				   unsigned long initrd_len,
>>>    				   const char *cmdline, size_t extra_fdt_size);
>>> -int ima_get_kexec_buffer(void **addr, size_t *size);
>>> -int ima_free_kexec_buffer(void);
>>>    #else /* CONFIG_OF */
>>>    static inline void of_core_init(void)
>>> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
>>> index 13753136f03f..419dc405c831 100644
>>> --- a/security/integrity/ima/ima_kexec.c
>>> +++ b/security/integrity/ima/ima_kexec.c
>>> @@ -137,7 +137,7 @@ void ima_add_kexec_buffer(struct kimage *image)
>>>    /*
>>>     * Restore the measurement list from the previous kernel.
>>>     */
>>> -void ima_load_kexec_buffer(void)
>>> +void __init ima_load_kexec_buffer(void)
>>>    {
>>>    	void *kexec_buffer = NULL;
>>>    	size_t kexec_buffer_size = 0;