Re: [PATCH v6 6/7] ima: make the kexec extra memory configurable

Stefan Berger
2025-01-28T15:19:42Z

On 1/24/25 5:55 PM, steven chen wrote:
> The extra memory allocated for carrying the IMA measurement list across
> kexec is hard-coded as half a PAGE. Make it configurable.
>
> Define a Kconfig option, IMA_KEXEC_EXTRA_MEMORY_KB, to configure the
> extra memory (in kb) to be allocated for IMA measurements added during
> kexec soft reboot. Ensure the default value of the option is set such
> that extra half a page of memory for additional measurements is allocated
> for the additional measurements.
>
> Update ima_add_kexec_buffer() function to allocate memory based on the
> Kconfig option value, rather than the currently hard-coded one.
>
> From: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: steven chen <chenste@linux.microsoft.com>
> ---
> security/integrity/ima/Kconfig | 10 ++++++++++
> security/integrity/ima/ima_kexec.c | 16 ++++++++++------
> 2 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 475c32615006..7dd2ed8b2cdc 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -321,4 +321,14 @@ config IMA_DISABLE_HTABLE
> help
> This option disables htable to allow measurement of duplicate records.
>
> +config IMA_KEXEC_EXTRA_MEMORY_KB
> + int

int "Extra memory for IMA measurements added during kexec soft reboot"

Without the description I wasn't able to modify the value.

> + depends on IMA_KEXEC
> + default 0
> + help
> + IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
> + allocated (in kb) for IMA measurements added during kexec soft reboot.
> + If set to the default value, an extra half a page of memory for those
> + additional measurements will be allocated.
> +
> endif
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index d5f004cfeaec..c9c916f69ca7 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -128,22 +128,26 @@ void ima_add_kexec_buffer(struct kimage *image)
> .buf_min = 0, .buf_max = ULONG_MAX,
> .top_down = true };
> unsigned long binary_runtime_size;
> -
> + unsigned long extra_size;
> /* use more understandable variable names than defined in kbuf */
> void *kexec_buffer = NULL;
> size_t kexec_buffer_size = 0;
> int ret;
>
> /*
> - * Reserve an extra half page of memory for additional measurements
> - * added during the kexec load.
> + * Reserve extra memory for measurements added during kexec.
> */
> - binary_runtime_size = ima_get_binary_runtime_size();
> + if (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB <= 0)
> + extra_size = PAGE_SIZE / 2;
> + else
> + extra_size = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
> + binary_runtime_size = ima_get_binary_runtime_size() + extra_size;
> +
> if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
> kexec_segment_size = ULONG_MAX;
> else
> - kexec_segment_size = ALIGN(ima_get_binary_runtime_size() +
> - PAGE_SIZE / 2, PAGE_SIZE);
> + kexec_segment_size = ALIGN(binary_runtime_size, PAGE_SIZE);
> +
> if ((kexec_segment_size == ULONG_MAX) ||
> ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
> pr_err("Binary measurement list too large.\n");

With the changes to Kconfig:

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