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

Stefan Berger
2025-01-28T15:29:34Z

On 1/24/25 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.
>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: steven chen <chenste@linux.microsoft.com>
> ---
> security/integrity/ima/ima_kexec.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index c9c916f69ca7..d416ca0382cb 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);
> }
>
> +static 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);
> +
> + ima_measure_critical_data("ima_kexec", event_name, ima_kexec_event,
> + strlen(ima_kexec_event), false, NULL, 0);
> +}
> +
> static int ima_alloc_kexec_file_buf(size_t segment_size)
> {
> /*
> @@ -60,6 +80,7 @@ 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;
> }
> @@ -206,6 +227,8 @@ static int ima_update_kexec_buffer(struct notifier_block *self,
>
> if (ret)
> pr_err("Dump measurements failed. Error:%d\n", ret);
> + else
> + ima_measure_kexec_event("kexec_execute");
>
> if (buf_size != 0)
> memcpy(ima_kexec_buffer, buf, buf_size);

I have been doing kexec's (on ppc64 KVM) applying one patch after
another in this series and then testing with this command:

evmctl ima_measurement --ignore-violations
/sys/kernel/security/ima/binary_runtime_measurements

Unfortunately it breaks at this patch. I am not sure what it is due to.