ram-wipe - Wipe RAM on shutdown and reboot
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Preventing Cold Boot Attacks. Wipe RAM at shutdown to prevent information extraction from memory.
ram-wipe is a software project that aims to defend against cold boot attacks by wiping the contents of a computer's random access memory (RAM) when the computer is shut down or restarted. This software prevents attackers from accessing sensitive information that may have been stored in the RAM by erasing it entirely, attempting to make it impossible for anyone to retrieve it. ram-wipe is particularly useful for organizations that handle sensitive information and require an additional layer of protection against security breaches. By ensuring that the RAM is wiped clean after shutdown or restart, ram-wipe helps safeguard against the risks posed by cold boot attacks, thereby providing an enhanced level of security.
Introduction[edit]
Cold boot attacks are a known attack vector since at least 2008. [1] Finally in 2023, 15 years later, a mitigation for cold boot attacks, the ram-wipe package has been made available, which is easily usable on Debian, Kicksecure ™, perhaps other Linux distributions as well as ram-wipe could relatively easily ported to other Linux distributions and/or hardware architectures.
At least since 2011, the Linux live operating system Tails
implemented wiping the ram at shutdown [2] but its memory erasure design documentation mentions several limitations. While Tails' implementation could in theory be ported to other Linux distributions such as Debian, Fedora and others, this at time of writing has never been done.
With ram-wipe there is now a standalone wipe RAM at shutdown software solution, with very few dependencies. In principle, it can run on Debian and derivatives of Debian such as Ubuntu. It might be relatively easy for other Linux distributions to package ram-wipe because it is implemented as a dracut module and dracut is already available (or even the default) for many Linux distributions. What's missing is probably only distribution maintainer doing the usual packaging work for their distribution.
As for initramfs-tools by ram-wipe, see Status of initramfs-tools Support.
See also Differences of security-misc Wipe RAM versus Tails Memory Erasure.
Installation of ram-wipe[edit]
Warning: This is for testers-only!
1. Migrate to dracut. [3]
It's required to migrate to dracut if not already done.
Warning:
There's a big chance of the system getting unbootable because this changes the initrd creation tool.
- There are currently issues with migration to dracut if using full disk encryption. Bug reports:
- This might also only happen on systems with unusual configurations.
It is prudent to always have a backup and be careful.
If there are any issues with dracut, please do not report such issues here since these are totally unspecific to Kicksecure.
Install dracut. To accomplish that, the following steps A. to D. need to be done.
A. Update the package lists.
sudo apt update
B. Upgrade the system.
sudo apt full-upgrade
C. Install the dracut package.
Using apt command line parameter --no-install-recommends is in most cases optional.
sudo apt install --no-install-recommends dracut
D. Done.
The procedure of installing dracut is complete.
2. Reboot.
This is to test if dracut is functional.
3. Add Kicksecure APT repository.
NOTE: Users of Kicksecure can skip this step.
1. Download the Signing Key.
wget https://www.kicksecure.com/keys/derivative.asc
2. Optional: Check the Signing Key for better security.
3. Add Kicksecure signing key.
sudo cp derivative.asc /usr/share/keyrings/derivative.asc
4. Kicksecure APT repository choices.
Optional: See Kicksecure Packages for Debian Hosts and Kicksecure Host Enhancements instead of the next step for more secure and complex options.
5. Add Kicksecure APT repository.
echo "deb [signed-by=/usr/share/keyrings/derivative.asc] https://deb.kicksecure.com bullseye main contrib non-free" | sudo tee /etc/apt/sources.list.d/derivative.list
4. Install ram-wipe.
Install ram-wipe. To accomplish that, the following steps A. to D. need to be done.
A. Update the package lists.
sudo apt update
B. Upgrade the system.
sudo apt full-upgrade
C. Install the ram-wipe package.
Using apt command line parameter --no-install-recommends is in most cases optional.
sudo apt install --no-install-recommends ram-wipe
D. Done.
The procedure of installing ram-wipe is complete.
5. Done.
The process of installing ram-wipe has been completed.
Sample Printout[edit]
Boot Printout[edit]
Loading Linux 5.10.0-21-amd64 ... Loading initial ramdisk ... [ 1.901368] dracut-pre-udev[164]: INFO: wipe-ram-exit.sh: Skip, because wiperamexit kernel parameter is unset, OK. [ 1.937683] dracut-pre-trigger[186]: INFO: wipe-ram-exit-needshutdown.sh: normal boot... [ 3.899932] dracut-pre-pivot[355]: INFO: wipe-ram-needshutdown.sh: wiperam=force kernel parameter detected, OK. [ 3.901024] dracut-pre-pivot[355]: INFO: wipe-ram-needshutdown.sh: Calling dracut function need_shutdown to drop back into initramfs at shutdown, OK. [ 5.633977] cold-boot-attack-defense-status[600]: /usr/libexec/ram-wipe/cold-boot-attack-defense-status: INFO: Will run at shutdown, ok.
Shutdown Printout[edit]
cold-boot-attack-defense-kexec-prepare[1384]: INFO: wiperamaction: poweroff [ 42.122900] cold-boot-attack-defense-kexec-prepare[1384]: kexec --load /boot//vmlinuz-5.10.0-21-amd64 --initrd=/boot//initrd.img-5.10.0-21-amd64 --reuse-cmdline --append=wiperamexit=yes wiperamaction=poweroff [ 42.628331] cold-boot-attack-defense-kexec-prepare[1384]: OK. [ 43.252013] dracut Warning: Killing all remaining processes dracut Warning: Killing all remaining processes [ 43.343133] dracut Warning: Unmounted /oldroot. [ 43.356100] dracut INFO: wipe-ram.sh: wiperam=force detected, OK. dracut INFO: wipe-ram.sh: wiperam=force detected, OK. [ 43.359471] dracut INFO: wipe-ram.sh: Cold boot attack defense... Starting first RAM wipe pass on shutdown... (1/2) dracut INFO: wipe-ram.sh: Cold boot attack defense... Starting first RAM wipe pass on shutdown... (1/2) Starting Wiping the memory, press Control-C to abort earlier. Help: "sdmem -h" Wipe mode is insecure (one pass with 0x00) ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* ********************************************************************************************************************* [ 45.821857] sdmem invoked oom-killer: gfp_mask=0x100dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), order=0, oom_score_adj=0 [ 45.823166] CPU: 2 PID: 1555 Comm: sdmem Tainted: G OE 5.10.0-21-amd64 #1 Debian 5.10.162-1 [ 45.832277] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 [ 45.833921] Call Trace: [ 45.834447] dump_stack+0x6b/0x83 [ 45.834947] dump_header+0x4a/0x1f4 [ 45.835366] oom_kill_process.cold+0xb/0x10 [ 45.836044] out_of_memory+0x1bd/0x4e0 [ 45.836555] __alloc_pages_slowpath.constprop.0+0xbcc/0xc90 [ 45.837541] ? _raw_spin_unlock_irqrestore+0x11/0x20 [ 45.838426] __alloc_pages_nodemask+0x2de/0x310 [ 45.839773] alloc_pages_vma+0x80/0x270 [ 45.840287] handle_mm_fault+0xead/0x1c00 [ 45.840895] do_user_addr_fault+0x1b8/0x400 [ 45.841461] exc_page_fault+0x78/0x160 [ 45.841958] ? asm_exc_page_fault+0x8/0x30 [ 45.842353] asm_exc_page_fault+0x1e/0x30 [ 45.842726] RIP: 0033:0x7283823800b3 [ 45.843114] Code: 47 10 f3 0f 7f 44 17 e0 f3 0f 7f 47 20 f3 0f 7f 44 17 d0 f3 0f 7f 47 30 f3 0f 7f 44 17 c0 48 01 fa 48 83 e2 c0 48 39 d1 74 c0 <66> 0f 7f 01 66 0f 7f 41 10 66 0f 7f 41 20 66 0f 7f 41 30 48 83 c1 [ 45.845266] RSP: 002b:00007ffee2e30728 EFLAGS: 00010206 [ 45.845898] RAX: 000057d0fb8c74e0 RBX: 000057cfb761d280 RCX: 000057d0fb8d5000 [ 45.846797] RDX: 000057d0fb8d74c0 RSI: 0000000000000000 RDI: 000057d0fb8c74e0 [ 45.847665] RBP: 00007ffee2fe0938 R08: 000057d0fb8c74e0 R09: 00007283824aabe0 [ 45.848535] R10: 000000000000007e R11: 0000000000000000 R12: 000057d0fb8b74d0 [ 45.855760] R13: 0000000000000000 R14: 0000000000000008 R15: 0000000000000000 [ 45.856702] Mem-Info: [ 45.857046] active_anon:721 inactive_anon:946309 isolated_anon:0 [ 45.857046] active_file:0 inactive_file:0 isolated_file:0 [ 45.857046] unevictable:0 dirty:0 writeback:0 [ 45.857046] slab_reclaimable:3024 slab_unreclaimable:6463 [ 45.857046] mapped:722 shmem:10150 pagetables:2600 bounce:0 [ 45.857046] free:21817 free_pcp:907 free_cma:0 [ 45.860910] Node 0 active_anon:2884kB inactive_anon:3785236kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:2888kB dirty:0kB writeback:0kB shmem:40600kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB kernel_stack:1440kB all_unreclaimable? yes [ 45.864676] Node 0 DMA free:15396kB min:268kB low:332kB high:396kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [ 45.867903] lowmem_reserve[]: 0 3454 3894 3894 3894 [ 45.868595] Node 0 DMA32 free:61244kB min:59696kB low:74620kB high:89544kB reserved_highatomic:0KB active_anon:160kB inactive_anon:3428080kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:3653568kB managed:3558516kB mlocked:0kB pagetables:0kB bounce:0kB free_pcp:3212kB local_pcp:328kB free_cma:0kB [ 45.871791] lowmem_reserve[]: 0 0 440 440 440 [ 45.873020] Node 0 Normal free:10628kB min:11708kB low:13608kB high:15508kB reserved_highatomic:0KB active_anon:2724kB inactive_anon:356824kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:524288kB managed:451212kB mlocked:0kB pagetables:10400kB bounce:0kB free_pcp:416kB local_pcp:220kB free_cma:0kB [ 45.878204] lowmem_reserve[]: 0 0 0 0 0 [ 45.879309] Node 0 DMA: 1*4kB (U) 0*8kB 0*16kB 1*32kB (U) 2*64kB (U) 1*128kB (U) 1*256kB (U) 1*512kB (U) 0*1024kB 1*2048kB (M) 3*4096kB (M) = 15396kB [ 45.882343] Node 0 DMA32: 359*4kB (UE) 329*8kB (UME) 206*16kB (UME) 83*32kB (UE) 35*64kB (UE) 5*128kB (UE) 5*256kB (UME) 4*512kB (E) 2*1024kB (UE) 1*2048kB (U) 10*4096kB (M) = 61284kB [ 45.885362] Node 0 Normal: 56*4kB (UME) 101*8kB (UME) 212*16kB (UME) 120*32kB (UME) 43*64kB (UME) 2*128kB (E) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 11272kB [ 45.898876] 10150 total pagecache pages [ 45.900518] 0 pages in swap cache [ 45.901931] Swap cache stats: add 0, delete 0, find 0/0 [ 45.903342] Free swap = 0kB [ 45.904461] Total swap = 0kB [ 45.905653] 1048462 pages RAM [ 45.906944] 0 pages HighMem/MovableOnly [ 45.908826] 42053 pages reserved [ 45.909921] 0 pages hwpoisoned [ 45.911114] Out of memory: Killed process 1555 (sdmem) total-vm:5283280kB, anon-rss:3745880kB, file-rss:4kB, shmem-rss:1232kB, UID:0 pgtables:10376kB oom_score_adj:0 /usr/sbin/wipe-ram-shutdown-helper: line 23: 1555 Killed sdmem -l -l -v [ 46.386353] dracut INFO: wipe-ram.sh: First RAM wipe pass completed, OK. (1/2) dracut INFO: wipe-ram.sh: First RAM wipe pass completed, OK. (1/2) [ 46.393183] dracut INFO: wipe-ram.sh: Checking if there are still mounted encrypted disks... dracut INFO: wipe-ram.sh: Checking if there are still mounted encrypted disks... [ 46.399212] dracut INFO: wipe-ram.sh: Success, there are no more mounted encrypted disks, OK. dracut INFO: wipe-ram.sh: Success, there are no more mounted encrypted disks, OK. [ 46.402562] dracut INFO: wipe-ram.sh: Now running 'kexec --exec'... dracut INFO: wipe-ram.sh: Now running 'kexec --exec'... [ 1.666717] dracut-pre-udev[162]: INFO: wipe-ram-exit.sh: wiperamexit=yes kernel parameter detected, OK. [ 1.667591] dracut-pre-udev[162]: INFO: wipe-ram-exit.sh: Cold boot attack defense... Starting second RAM wipe pass on shutdown... (2/2) [FAILED] Failed to start dracut pre-udev hook. [ 3.902631] dracut-pre-trigger[176]: INFO: wipe-ram-exit-needshutdown.sh: poweroff... [ 3.905037] dracut-pre-trigger[179]: Powering off. [ 3.906967] reboot: Power down
ram-wipe Known Issues[edit]
Wipe mode is insecure (one pass with 0x00): This might be a textual output bug insdmem. It might be inspired by the Gutmann method, which is an algorithm for securely erasing the contents of computer hard disk drives. Gutmann, the inventor, said quote wikipedia:
He said "In the time since this paper was published, some people have treated the 35-pass overwrite technique described in it more as a kind of voodoo incantation to banish evil spirits than the result of a technical analysis of drive encoding techniques"
- No research papers that found that RAM has to be overwritten with more than one pass exist to the knowledge of the author.
- Several passes of RAM wipe would increase the reboot/shutdown time, have no documented benefit, increase the reboot time even more and therefore make this solution unusable.
- sdmem is unmaintained upstream?
Hi, this isn't a project that I'm actually maintaining, I put it up here for archiving purposes. Its old code and likely needs a lot of work. When I get around to doing some stuff on it, I'll work support for that in, but I can't say when that will be, sorry. Will keep the issue open though since its a good suggestion.
- If
memtest86+ feature request kexec into memtest86+ for RAM Wipe and reboot/poweroff - Cold Boot Attack Defense would get implemented, this would provide a much better tool for wiping the RAM than sdmem.
[FAILED] Failed to start dracut pre-udev hook.: This is happening becausesdmemduring the dracut pre-udev hook gets killed by Linux's out of memory (OOM) killer because it is using the maximum of available RAM.sdmem invoked oom-killer: similar to above.- The output by
sdmem, its progress meter and the OOM killing looks unnecessarily scary and is user unfriendly. - In VirtualBox, newly kexec'd kernel that runs a second RAM wipe pass (2/2) does not show any output. This is non-ideal but only a small issue since ram-wipe does not need to be used inside VMs anyhow except for testing. The RAM wipe functionality during shutdown and after kexec can be confirmed using a serial console. On real hardware, this issue did not occur yet.
- Wiping the video RAM (the RAM of the graphics card) has not been implemented anywhere to the knowledge of the author. [4]
- ram-wipe security testing has yet to be done, see ram-wipe development TODO. Check back later.
- While dracut bug dracut should unmount the root encrypted disk
cryptsetup luksCloseduring shutdown is independent from ram wipe, might affect negatively the RAM wiping process.
- Unmounting the root encrypted disk is important for RAM wipe at shutdown to make sure (or at least increase chances) of Linux releasing the LUKS disk encryption key from RAM.
- ram-wipe comes with code to notify the user of this situation should it apply to the user's system.
- The user would be able to read
wipe-ram.sh: There are still mounted encrypted disks! RAM wipe incomplete!. - In result this means that the first RAM wipe pass (1/2) during poweroff/reboot might not wipe the root disk's full disk encryption key from RAM. Hopefully it would be wiped from RAM after kexec into a new kernel and the second RAM wipe pass (2/2).
- Obviously it would be much better if dracut would cleanly unmount the root encrypted disk. If you are a developer, please consider contributing a bugfix directly to dracut upstream.
Contributor help is needed and welcome to fix these issues.
Development[edit]
- Cold Boot Attack Defense - RAM Wipe Design Documentation
- Is RAM Wipe possible? Cold Boot Attack Defense
Footnotes[edit]
- ↑
https://en.wikipedia.org/w/index.php?title=Cold_boot_attack&oldid=249088610
- ↑
https://web.archive.org/web/20110423165633/https://tails.boum.org/contribute/design/memory_erasure/
- ↑ Since ram-wipe is unavailable for initramfs-tools the user needs to migrate to dracut, the only supported initrd creator by ram-wipe.
- ↑
Erase video memory on shutdown
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