The bits set in x86_spec_ctrl_mask are used to calculate the guest's value
of SPEC_CTRL that is written to the MSR before VMENTRY, and control which
mitigations the guest can enable. In the case of SSBD, unless the host has
enabled SSBD always on mode (by passing "spec_store_bypass_disable=on" in
the kernel parameters), the SSBD bit is not set in the mask and the guest
can not properly enable the SSBD always on mitigation mode.
This has been confirmed by running the SSBD PoC on a guest using the SSBD
always on mitigation mode (booted with kernel parameter
"spec_store_bypass_disable=on"), and verifying that the guest is vulnerable
unless the host is also using SSBD always on mode. In addition, the guest
OS incorrectly reports the SSB vulnerability as mitigated.
Always set the SSBD bit in x86_spec_ctrl_mask when the host CPU supports
it, allowing the guest to use SSBD whether or not the host has chosen to
enable the mitigation in any of its modes.
Fixes: be6fcb5478e9 ("x86/bugs: Rework spec_ctrl base and mask logic")
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Mark Kanda <mark.kanda@oracle.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: bp@alien8.de
Cc: rkrcmar@redhat.com
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1560187210-11054-1-git-send-email-alejandro.j.jimenez@oracle.com
Pull x86 MDS mitigations from Thomas Gleixner:
"Microarchitectural Data Sampling (MDS) is a hardware vulnerability
which allows unprivileged speculative access to data which is
available in various CPU internal buffers. This new set of misfeatures
has the following CVEs assigned:
CVE-2018-12126 MSBDS Microarchitectural Store Buffer Data Sampling
CVE-2018-12130 MFBDS Microarchitectural Fill Buffer Data Sampling
CVE-2018-12127 MLPDS Microarchitectural Load Port Data Sampling
CVE-2019-11091 MDSUM Microarchitectural Data Sampling Uncacheable Memory
MDS attacks target microarchitectural buffers which speculatively
forward data under certain conditions. Disclosure gadgets can expose
this data via cache side channels.
Contrary to other speculation based vulnerabilities the MDS
vulnerability does not allow the attacker to control the memory target
address. As a consequence the attacks are purely sampling based, but
as demonstrated with the TLBleed attack samples can be postprocessed
successfully.
The mitigation is to flush the microarchitectural buffers on return to
user space and before entering a VM. It's bolted on the VERW
instruction and requires a microcode update. As some of the attacks
exploit data structures shared between hyperthreads, full protection
requires to disable hyperthreading. The kernel does not do that by
default to avoid breaking unattended updates.
The mitigation set comes with documentation for administrators and a
deeper technical view"
* 'x86-mds-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
x86/speculation/mds: Fix documentation typo
Documentation: Correct the possible MDS sysfs values
x86/mds: Add MDSUM variant to the MDS documentation
x86/speculation/mds: Add 'mitigations=' support for MDS
x86/speculation/mds: Print SMT vulnerable on MSBDS with mitigations off
x86/speculation/mds: Fix comment
x86/speculation/mds: Add SMT warning message
x86/speculation: Move arch_smt_update() call to after mitigation decisions
x86/speculation/mds: Add mds=full,nosmt cmdline option
Documentation: Add MDS vulnerability documentation
Documentation: Move L1TF to separate directory
x86/speculation/mds: Add mitigation mode VMWERV
x86/speculation/mds: Add sysfs reporting for MDS
x86/speculation/mds: Add mitigation control for MDS
x86/speculation/mds: Conditionally clear CPU buffers on idle entry
x86/kvm/vmx: Add MDS protection when L1D Flush is not active
x86/speculation/mds: Clear CPU buffers on exit to user
x86/speculation/mds: Add mds_clear_cpu_buffers()
x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests
x86/speculation/mds: Add BUG_MSBDS_ONLY
...
Pull speculation mitigation update from Ingo Molnar: "This adds the "mitigations=" bootline option, which offers a cross-arch set of options that will work on x86, PowerPC and s390 that will map to the arch specific option internally" * 'core-speculation-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: s390/speculation: Support 'mitigations=' cmdline option powerpc/speculation: Support 'mitigations=' cmdline option x86/speculation: Support 'mitigations=' cmdline option cpu/speculation: Add 'mitigations=' cmdline option
Some of the recently added const tables use __initdata which causes section
attribute conflicts.
Use __initconst instead.
Fixes: fa1202ef2243 ("x86/speculation: Add command line control")
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190330004743.29541-9-andi@firstfloor.org
Add MDS to the new 'mitigations=' cmdline option. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Pull in the command line updates from the tip tree so the MDS parts can be added.
Configure x86 runtime CPU speculation bug mitigations in accordance with the 'mitigations=' cmdline option. This affects Meltdown, Spectre v2, Speculative Store Bypass, and L1TF. The default behavior is unchanged. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86) Reviewed-by: Jiri Kosina <jkosina@suse.cz> Cc: Borislav Petkov <bp@alien8.de> Cc: "H . Peter Anvin" <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jiri Kosina <jikos@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Jon Masters <jcm@redhat.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: linuxppc-dev@lists.ozlabs.org Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: linux-s390@vger.kernel.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-arch@vger.kernel.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Tyler Hicks <tyhicks@canonical.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Steven Price <steven.price@arm.com> Cc: Phil Auld <pauld@redhat.com> Link: https://lkml.kernel.org/r/6616d0ae169308516cfdf5216bedd169f8a8291b.1555085500.git.jpoimboe@redhat.com
This code is only for CPUs which are affected by MSBDS, but are *not* affected by the other two MDS issues. For such CPUs, enabling the mds_idle_clear mitigation is enough to mitigate SMT. However if user boots with 'mds=off' and still has SMT enabled, we should not report that SMT is mitigated: $cat /sys//devices/system/cpu/vulnerabilities/mds Vulnerable; SMT mitigated But rather: Vulnerable; SMT vulnerable Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Tyler Hicks <tyhicks@canonical.com> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lkml.kernel.org/r/20190412215118.294906495@localhost.localdomain
s/L1TF/MDS/ Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Tyler Hicks <tyhicks@canonical.com> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
MDS is vulnerable with SMT. Make that clear with a one-time printk whenever SMT first gets enabled. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Tyler Hicks <tyhicks@canonical.com> Acked-by: Jiri Kosina <jkosina@suse.cz>