linux-stable.git/Documentation/admin-guide, branch v6.6.26

x86/bhi: Mitigate KVM by default

2024-04-10T14:36:08+00:00

commit 95a6ccbdc7199a14b71ad8901cb788ba7fb5167b upstream.

BHI mitigation mode spectre_bhi=auto does not deploy the software
mitigation by default. In a cloud environment, it is a likely scenario
where userspace is trusted but the guests are not trusted. Deploying
system wide mitigation in such cases is not desirable.

Update the auto mode to unconditionally mitigate against malicious
guests. Deploy the software sequence at VMexit in auto mode also, when
hardware mitigation is not available. Unlike the force =on mode,
software sequence is not deployed at syscalls in auto mode.

Suggested-by: Alexandre Chartre 
Signed-off-by: Pawan Gupta 
Signed-off-by: Daniel Sneddon 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexandre Chartre 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Daniel Sneddon 
Signed-off-by: Greg Kroah-Hartman

x86/bhi: Add BHI mitigation knob

2024-04-10T14:36:08+00:00

commit ec9404e40e8f36421a2b66ecb76dc2209fe7f3ef upstream.

Branch history clearing software sequences and hardware control
BHI_DIS_S were defined to mitigate Branch History Injection (BHI).

Add cmdline spectre_bhi={on|off|auto} to control BHI mitigation:

 auto - Deploy the hardware mitigation BHI_DIS_S, if available.
 on   - Deploy the hardware mitigation BHI_DIS_S, if available,
        otherwise deploy the software sequence at syscall entry and
	VMexit.
 off  - Turn off BHI mitigation.

The default is auto mode which does not deploy the software sequence
mitigation.  This is because of the hardening done in the syscall
dispatch path, which is the likely target of BHI.

Signed-off-by: Pawan Gupta 
Signed-off-by: Daniel Sneddon 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexandre Chartre 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Daniel Sneddon 
Signed-off-by: Greg Kroah-Hartman

x86/Kconfig: Remove CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT

2024-04-03T13:28:50+00:00

commit 29956748339aa8757a7e2f927a8679dd08f24bb6 upstream.

It was meant well at the time but nothing's using it so get rid of it.

Signed-off-by: Borislav Petkov (AMD) 
Acked-by: Ard Biesheuvel 
Link: https://lore.kernel.org/r/20240202163510.GDZb0Zvj8qOndvFOiZ@fat_crate.local
Signed-off-by: Greg Kroah-Hartman

x86/rfds: Mitigate Register File Data Sampling (RFDS)

2024-03-15T14:48:22+00:00

commit 8076fcde016c9c0e0660543e67bff86cb48a7c9c upstream.

RFDS is a CPU vulnerability that may allow userspace to infer kernel
stale data previously used in floating point registers, vector registers
and integer registers. RFDS only affects certain Intel Atom processors.

Intel released a microcode update that uses VERW instruction to clear
the affected CPU buffers. Unlike MDS, none of the affected cores support
SMT.

Add RFDS bug infrastructure and enable the VERW based mitigation by
default, that clears the affected buffers just before exiting to
userspace. Also add sysfs reporting and cmdline parameter
"reg_file_data_sampling" to control the mitigation.

For details see:
Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst

Signed-off-by: Pawan Gupta 
Signed-off-by: Dave Hansen 
Reviewed-by: Thomas Gleixner 
Acked-by: Josh Poimboeuf 
Signed-off-by: Greg Kroah-Hartman

Documentation/hw-vuln: Add documentation for RFDS

2024-03-15T14:48:22+00:00

commit 4e42765d1be01111df0c0275bbaf1db1acef346e upstream.

Add the documentation for transient execution vulnerability Register
File Data Sampling (RFDS) that affects Intel Atom CPUs.

Signed-off-by: Pawan Gupta 
Signed-off-by: Dave Hansen 
Reviewed-by: Thomas Gleixner 
Acked-by: Josh Poimboeuf 
Signed-off-by: Greg Kroah-Hartman

docs: kernel_abi.py: fix command injection

2024-02-01T00:18:54+00:00

commit 3231dd5862779c2e15633c96133a53205ad660ce upstream.

The kernel-abi directive passes its argument straight to the shell.
This is unfortunate and unnecessary.

Let's always use paths relative to $srctree/Documentation/ and use
subprocess.check_call() instead of subprocess.Popen(shell=True).

This also makes the code shorter.

Link: https://fosstodon.org/@jani/111676532203641247
Reported-by: Jani Nikula 
Cc: stable@vger.kernel.org
Signed-off-by: Vegard Nossum 
Signed-off-by: Jonathan Corbet 
Link: https://lore.kernel.org/r/20231231235959.3342928-2-vegard.nossum@oracle.com
Signed-off-by: Greg Kroah-Hartman

docs: kernel_feat.py: fix potential command injection

2024-02-01T00:18:46+00:00

[ Upstream commit c48a7c44a1d02516309015b6134c9bb982e17008 ]

The kernel-feat directive passes its argument straight to the shell.
This is unfortunate and unnecessary.

Let's always use paths relative to $srctree/Documentation/ and use
subprocess.check_call() instead of subprocess.Popen(shell=True).

This also makes the code shorter.

This is analogous to commit 3231dd586277 ("docs: kernel_abi.py: fix
command injection") where we did exactly the same thing for
kernel_abi.py, somehow I completely missed this one.

Link: https://fosstodon.org/@jani/111676532203641247
Reported-by: Jani Nikula 
Signed-off-by: Vegard Nossum 
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Corbet 
Link: https://lore.kernel.org/r/20240110174758.3680506-1-vegard.nossum@oracle.com
Signed-off-by: Sasha Levin

smp,csd: Throw an error if a CSD lock is stuck for too long

2023-11-28T17:19:36+00:00

[ Upstream commit 94b3f0b5af2c7af69e3d6e0cdd9b0ea535f22186 ]

The CSD lock seems to get stuck in 2 "modes". When it gets stuck
temporarily, it usually gets released in a few seconds, and sometimes
up to one or two minutes.

If the CSD lock stays stuck for more than several minutes, it never
seems to get unstuck, and gradually more and more things in the system
end up also getting stuck.

In the latter case, we should just give up, so the system can dump out
a little more information about what went wrong, and, with panic_on_oops
and a kdump kernel loaded, dump a whole bunch more information about what
might have gone wrong.  In addition, there is an smp.panic_on_ipistall
kernel boot parameter that by default retains the old behavior, but when
set enables the panic after the CSD lock has been stuck for more than
the specified number of milliseconds, as in 300,000 for five minutes.

[ paulmck: Apply Imran Khan feedback. ]
[ paulmck: Apply Leonardo Bras feedback. ]

Link: https://lore.kernel.org/lkml/bc7cc8b0-f587-4451-8bcd-0daae627bcc7@paulmck-laptop/
Signed-off-by: Rik van Riel 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Imran Khan 
Reviewed-by: Leonardo Bras 
Cc: Peter Zijlstra 
Cc: Valentin Schneider 
Cc: Juergen Gross 
Cc: Jonathan Corbet 
Cc: Randy Dunlap 
Signed-off-by: Sasha Levin

x86/srso: Fix vulnerability reporting for missing microcode

2023-11-20T10:58:52+00:00

[ Upstream commit dc6306ad5b0dda040baf1fde3cfd458e6abfc4da ]

The SRSO default safe-ret mitigation is reported as "mitigated" even if
microcode hasn't been updated.  That's wrong because userspace may still
be vulnerable to SRSO attacks due to IBPB not flushing branch type
predictions.

Report the safe-ret + !microcode case as vulnerable.

Also report the microcode-only case as vulnerable as it leaves the
kernel open to attacks.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Ingo Molnar 
Signed-off-by: Borislav Petkov (AMD) 
Acked-by: Borislav Petkov (AMD) 
Link: https://lore.kernel.org/r/a8a14f97d1b0e03ec255c81637afdf4cf0ae9c99.1693889988.git.jpoimboe@kernel.org
Signed-off-by: Sasha Levin

mm, memcg: reconsider kmem.limit_in_bytes deprecation

2023-09-30T00:20:47+00:00

This reverts commits 86327e8eb94c ("memcg: drop kmem.limit_in_bytes") and
partially reverts 58056f77502f ("memcg, kmem: further deprecate
kmem.limit_in_bytes") which have incrementally removed support for the
kernel memory accounting hard limit.  Unfortunately it has turned out that
there is still userspace depending on the existence of
memory.kmem.limit_in_bytes [1].  The underlying functionality is not
really required but the non-existent file just confuses the userspace
which fails in the result.  The patch to fix this on the userspace side
has been submitted but it is hard to predict how it will propagate through
the maze of 3rd party consumers of the software.

Now, reverting alone 86327e8eb94c is not an option because there is
another set of userspace which cannot cope with ENOTSUPP returned when
writing to the file.  Therefore we have to go and revisit 58056f77502f as
well.  There are two ways to go ahead.  Either we give up on the
deprecation and fully revert 58056f77502f as well or we can keep
kmem.limit_in_bytes but make the write a noop and warn about the fact. 
This should work for both known breaking workloads which depend on the
existence but do not depend on the hard limit enforcement.

Note to backporters to stable trees.  a8c49af3be5f ("memcg: add per-memcg
total kernel memory stat") introduced in 4.18 has added memcg_account_kmem
so the accounting is not done by obj_cgroup_charge_pages directly for v1
anymore.  Prior kernels need to add it explicitly (thanks to Johannes for
pointing this out).

[akpm@linux-foundation.org: fix build - remove unused local]
Link: http://lkml.kernel.org/r/20230920081101.GA12096@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net [1]
Link: https://lkml.kernel.org/r/ZRE5VJozPZt9bRPy@dhcp22.suse.cz
Fixes: 86327e8eb94c ("memcg: drop kmem.limit_in_bytes")
Fixes: 58056f77502f ("memcg, kmem: further deprecate kmem.limit_in_bytes")
Signed-off-by: Michal Hocko 
Acked-by: Shakeel Butt 
Acked-by: Johannes Weiner 
Cc: Greg Kroah-Hartman 
Cc: Jeremi Piotrowski 
Cc: Muchun Song 
Cc: Roman Gushchin 
Cc: Tejun heo 
Cc: 
Signed-off-by: Andrew Morton