linux-kernel - Re: [PATCH v8 7/7] ima: measure kexec load and exec events as critical data

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Message-ID: <152e2efc-732f-40bf-9aeb-6e50faa018c0@linux.ibm.com>
Date: Wed, 19 Feb 2025 11:23:40 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: steven chen <chenste@...ux.microsoft.com>, zohar@...ux.ibm.com,
        roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
        eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
        code@...icks.com, bauermann@...abnow.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
        James.Bottomley@...senPartnership.com, bhe@...hat.com,
        vgoyal@...hat.com, dyoung@...hat.com
Subject: Re: [PATCH v8 7/7] ima: measure kexec load and exec events as
 critical data



On 2/18/25 5:55 PM, steven chen wrote:
> The amount of memory allocated at kexec load, even with the extra memory
> allocated, might not be large enough for the entire measurement list.  The
> indeterminate interval between kexec 'load' and 'execute' could exacerbate
> this problem.
> 
> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be
> measured as critical data at kexec 'load' and 'execute' respectively.
> Report the allocated kexec segment size, IMA binary log size and the
> runtime measurements count as part of those events.
> 
> These events, and the values reported through them, serve as markers in
> the IMA log to verify the IMA events are captured during kexec soft
> reboot.  The presence of a 'kexec_load' event in between the last two
> 'boot_aggregate' events in the IMA log implies this is a kexec soft
> reboot, and not a cold-boot. And the absence of 'kexec_execute' event
> after kexec soft reboot implies missing events in that window which
> results in inconsistency with TPM PCR quotes, necessitating a cold boot
> for a successful remote attestation.
> 
> The 'kexec_load' event IMA log can be found using the following command:
> sudo cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements |
>     grep kexec_load
> 
> The 'kexec_load' event IMA log can be found using the following command:
> sudo cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements |
>     grep kexec_execute
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
> ---
>   security/integrity/ima/ima.h       |  6 ++++++
>   security/integrity/ima/ima_kexec.c | 21 +++++++++++++++++++++
>   security/integrity/ima/ima_queue.c |  5 +++++
>   3 files changed, 32 insertions(+)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 4428fcf42167..1452c98242a4 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -240,6 +240,12 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
>   				   unsigned long flags, bool create);
>   #endif
>   
> +#ifdef CONFIG_IMA_KEXEC
> +void ima_measure_kexec_event(const char *event_name);
> +#else
> +static inline void ima_measure_kexec_event(const char *event_name) {}
> +#endif
> +
>   /*
>    * The default binary_runtime_measurements list format is defined as the
>    * platform native format.  The canonical format is defined as little-endian.
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 6c8c203ad81e..8d0782e51ffa 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -17,6 +17,8 @@
>   #include "ima.h"
>   
>   #ifdef CONFIG_IMA_KEXEC
> +#define IMA_KEXEC_EVENT_LEN 256
> +
>   static struct seq_file ima_kexec_file;
>   static void *ima_kexec_buffer;
>   static size_t kexec_segment_size;
> @@ -36,6 +38,24 @@ static void ima_free_kexec_file_buf(struct seq_file *sf)
>   	ima_reset_kexec_file(sf);
>   }
>   
> +void ima_measure_kexec_event(const char *event_name)
> +{
> +	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
> +	size_t buf_size = 0;
> +	long len;
> +
> +	buf_size = ima_get_binary_runtime_size();
> +	len = atomic_long_read(&ima_htable.len);
> +
> +	scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> +		  "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
> +		 "ima_runtime_measurements_count=%ld;",
> +		 kexec_segment_size, buf_size, len);

Indentation and n = scnprintf(...), as Mimi mentioned in v7.

> +
> +	ima_measure_critical_data("ima_kexec", event_name, ima_kexec_event,
> +				  strlen(ima_kexec_event), false, NULL, 0);

Replace strlen(ima_kexec_event) with 'n'.

With these fixes:

Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>

> +}
> +
>   static int ima_alloc_kexec_file_buf(size_t segment_size)
>   {
>   	/*
> @@ -58,6 +78,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>   out:
>   	ima_kexec_file.read_pos = 0;
>   	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
> +	ima_measure_kexec_event("kexec_load");
>   
>   	return 0;
>   }
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index 3dfd178d4292..6afb46989cf6 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -241,6 +241,11 @@ static int ima_reboot_notifier(struct notifier_block *nb,
>   			       unsigned long action,
>   			       void *data)
>   {
> +#ifdef CONFIG_IMA_KEXEC
> +	if (action == SYS_RESTART && data && !strcmp(data, "kexec reboot"))
> +		ima_measure_kexec_event("kexec_execute");
> +#endif
> +
>   	ima_measurements_suspend();
>   
>   	return NOTIFY_DONE;