linux-kernel - Re: [PATCH v6 07/12] x86/cpu/keylocker: Load an internal wrapping key at boot-time

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Message-ID: <ac5de854-d274-92ab-a0fa-9a0e738a68fa@intel.com>
Date:   Mon, 8 May 2023 13:15:59 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>
CC:     "ebiggers@...nel.org" <ebiggers@...nel.org>,
        "gmazyland@...il.com" <gmazyland@...il.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...e.de" <bp@...e.de>, "mingo@...nel.org" <mingo@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Keany, Bernie" <bernie.keany@...el.com>,
        "Gairuboyina, Charishma1" <charishma1.gairuboyina@...el.com>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v6 07/12] x86/cpu/keylocker: Load an internal wrapping key
 at boot-time

On 5/8/2023 12:18 PM, Elliott, Robert (Servers) wrote:
> 
>> diff --git a/arch/x86/kernel/keylocker.c b/arch/x86/kernel/keylocker.c
> ...
>> +void __init destroy_keylocker_data(void)
>> +{
>> +     memset(&kl_setup.key, KEY_DESTROY, sizeof(kl_setup.key));
>> +}
> 
> That's a special value for garbage collected keyring keys assigned
> a keytype of ".dead". memzero() or memzero_explicit() might be better
> for this use case.
memzero() looks to be the same as memset() in x86:

$ git grep memzero arch/x86/ | grep define
arch/x86/boot/compressed/misc.c:#define memzero(s, n)   memset((s), 0, (n))

Instead, memzero_explicit() looks to be about the right call here:

/**
  * memzero_explicit - Fill a region of memory (e.g. sensitive
  *		      keying data) with 0s.
  ...
  * Note: usually using memset() is just fine (!), but in cases
  * where clearing out _local_ data at the end of a scope is
  * necessary, memzero_explicit() should be used instead in
  * order to prevent the compiler from optimising away zeroing.
  ...

Then,

void __init destroy_keylocker_data(void)
{
	memzero_explicit(&kl_setup.key, sizeof(kl_setup.key));
}

Thanks,
Chang