linux-kernel - Re: [PATCH v10 7/8] ima: make the kexec extra memory configurable

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Message-ID: <Z9uC9g+UaVAA/0tY@MiWiFi-R3L-srv>
Date: Thu, 20 Mar 2025 10:52:38 +0800
From: Baoquan He <bhe@...hat.com>
To: steven chen <chenste@...ux.microsoft.com>
Cc: zohar@...ux.ibm.com, stefanb@...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,
	madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
	James.Bottomley@...senpartnership.com, vgoyal@...hat.com,
	dyoung@...hat.com
Subject: Re: [PATCH v10 7/8] ima: make the kexec extra memory configurable

On 03/17/25 at 06:04pm, 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.
> 
> Suggested-by: Stefan Berger <stefanb@...ux.ibm.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> ---
>  security/integrity/ima/Kconfig     | 10 ++++++++++
>  security/integrity/ima/ima_kexec.c | 16 +++++++++++-----
>  2 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 475c32615006..d73c96c3c1c9 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 "Extra memory for IMA measurements added during kexec soft reboot"
> +	depends on IMA_KEXEC
> +	default 0

Is there range for this memory, e.g [0, max] and max will be a value
according to our current perception?

> +	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 of 0, an extra half 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 c390c745f882..0f214e41dd33 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -131,6 +131,7 @@ 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_memory;
>  
>  	/* use more understandable variable names than defined in kbuf */
>  	size_t kexec_buffer_size = 0;
> @@ -138,15 +139,20 @@ void ima_add_kexec_buffer(struct kimage *image)
>  	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_memory = PAGE_SIZE / 2;
> +	else
> +		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
> +
> +	binary_runtime_size = ima_get_binary_runtime_size() + extra_memory;
> +
>  	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");
> -- 
> 2.25.1
> 
>