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

Lakshmi Ramasubramanian
2022-05-17T17:19:51Z

>>> 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;