On Fri, 2023-12-15 at 17:07 -0800, Tushar Sugandhi wrote:
> There could be a potential mismatch between IMA measurements and TPM PCR
> quotes caused by the indeterminate interval between kexec 'load' and
> 'execute'. Memory allocated at kexec 'load' for IMA log buffer may run
> out. It can lead to missing events in the IMA log after a soft reboot to
> the new Kernel, resulting in TPM PCR quotes mismatch and remote
> attestation failures.
>
> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be
> measured as critical data at kexec 'load' and 'execute' respectively.
>
> These events serve as markers in the IMA log to verify the IMA events are
> captured between kexec 'load' and 'execute' window. 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 further successful remote attestation.
>
> Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> ---
> security/integrity/ima/ima_kexec.c | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 063da9c834a0..47da41a66dcc 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 128
> +
> struct seq_file ima_kexec_file;
> static void *ima_kexec_buffer;
> static size_t kexec_segment_size;
> @@ -33,6 +35,8 @@ void ima_free_kexec_file_buf(struct seq_file *sf)
>
> static int ima_alloc_kexec_file_buf(size_t segment_size)
> {
> + char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
> +
> /*
> * kexec 'load' may be called multiple times.
> * Free and realloc the buffer only if the segment_size is
> @@ -42,7 +46,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
> ima_kexec_file.size == segment_size &&
> ima_kexec_file.read_pos == 0 &&
> ima_kexec_file.count == sizeof(struct ima_kexec_hdr))
> - return 0;
> + goto out;
>
> ima_free_kexec_file_buf(&ima_kexec_file);
>
> @@ -55,6 +59,13 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
> ima_kexec_file.read_pos = 0;
> ima_kexec_file.count = sizeof(struct ima_kexec_hdr); /* reserved space */
>
> +out:
> + scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> + "kexec_segment_size=%lu;", segment_size);
> +
> + ima_measure_critical_data("ima_kexec", "kexec_load", ima_kexec_event,
> + strlen(ima_kexec_event), false, NULL, 0);
> +
> return 0;
> }
>
> @@ -179,6 +190,7 @@ void ima_add_kexec_buffer(struct kimage *image)
> static int ima_update_kexec_buffer(struct notifier_block *self,
> unsigned long action, void *data)
> {
> + char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
> void *buf = NULL;
> size_t buf_size;
> bool resume = false;
> @@ -194,6 +206,15 @@ static int ima_update_kexec_buffer(struct notifier_block *self,
> return ret;
> }
>
> + buf_size = ima_get_binary_runtime_size();
> + scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> + "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;",
> + kexec_segment_size, buf_size);
> +
> + ima_measure_critical_data("ima_kexec", "kexec_execute",
> + ima_kexec_event, strlen(ima_kexec_event),
> + false, NULL, 0);
> +
Please consider including the number of measurement records as well.
> ima_measurements_suspend();
>
> ret = ima_dump_measurement_list(&buf_size, &buf,
--
thanks,
Mimi
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