linux-kernel - Re: [PATCH RFC] Add a lockdown

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Message-ID: <a66a805c-3e1f-4b9a-a38e-aca84b8678a6@infradead.org>
Date:   Mon, 13 Nov 2023 20:01:26 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Kelvie Wong <kelvie@...vie.ca>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     linux-security-module <linux-security-module@...r.kernel.org>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH RFC] Add a lockdown_hibernate parameter

[add security & dhowells]

On 11/13/23 18:23, Kelvie Wong wrote:
> This allows the user to tell the kernel that they know better (namely,
> they secured their swap properly), and that it can enable hibernation.
> 
> I've been using this for about a year now, as it doesn't seem like
> proper secure hibernation was going to be implemented back then, and
> it's now been a year since I've been building my own kernels with this
> patch, so getting this upstreamed would save some CO2 from me building
> my own kernels every upgrade.
> 
> Some other not-me users have also tested the patch:
> 
> https://community.frame.work/t/guide-fedora-36-hibernation-with-enabled-secure-boot-and-full-disk-encryption-fde-decrypting-over-tpm2/25474/17
> 
> Signed-off-by: Kelvie Wong <kelvie@...vie.ca>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 +++++
>  kernel/power/hibernate.c                        | 10 +++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 426fa892d311..54785faba9e0 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2804,6 +2804,11 @@
>  			to extract confidential information from the kernel
>  			are also disabled.
>  
> +	lockdown_hibernate	[HIBERNATION]
> +			Enable hibernation even if lockdown is enabled. Enable this only if
> +			your swap is encrypted and secured properly, as an attacker can
> +			modify the kernel offline during hibernation.
> +
>  	locktorture.nreaders_stress= [KNL]
>  			Set the number of locking read-acquisition kthreads.
>  			Defaults to being automatically set based on the
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 89c71fce225d..2221c531d54c 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -36,6 +36,7 @@
>  #include "power.h"
>  
>  
> +static int lockdown_hibernate;
>  static int nocompress;
>  static int noresume;
>  static int nohibernate;
> @@ -82,7 +83,7 @@ void hibernate_release(void)
>  bool hibernation_available(void)
>  {
>  	return nohibernate == 0 &&
> -		!security_locked_down(LOCKDOWN_HIBERNATION) &&
> +		(lockdown_hibernate || !security_locked_down(LOCKDOWN_HIBERNATION)) &&
>  		!secretmem_active() && !cxl_mem_active();
>  }
>  
> @@ -1340,6 +1341,12 @@ static int __init nohibernate_setup(char *str)
>  	return 1;
>  }
>  
> +static int __init lockdown_hibernate_setup(char *str)
> +{
> +	lockdown_hibernate = 1;
> +	return 1;
> +}
> +
>  __setup("noresume", noresume_setup);
>  __setup("resume_offset=", resume_offset_setup);
>  __setup("resume=", resume_setup);
> @@ -1347,3 +1354,4 @@ __setup("hibernate=", hibernate_setup);
>  __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
> +__setup("lockdown_hibernate", lockdown_hibernate_setup);

-- 
~Randy