Merge tag 'x86-bugs-2022-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 MMIO stale data fixes from Thomas Gleixner:
 "Yet another hw vulnerability with a software mitigation: Processor
  MMIO Stale Data.

  They are a class of MMIO-related weaknesses which can expose stale
  data by propagating it into core fill buffers. Data which can then be
  leaked using the usual speculative execution methods.

  Mitigations include this set along with microcode updates and are
  similar to MDS and TAA vulnerabilities: VERW now clears those buffers
  too"

* tag 'x86-bugs-2022-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation/mmio: Print SMT warning
  KVM: x86/speculation: Disable Fill buffer clear within guests
  x86/speculation/mmio: Reuse SRBDS mitigation for SBDS
  x86/speculation/srbds: Update SRBDS mitigation selection
  x86/speculation/mmio: Add sysfs reporting for Processor MMIO Stale Data
  x86/speculation/mmio: Enable CPU Fill buffer clearing on idle
  x86/bugs: Group MDS, TAA & Processor MMIO Stale Data mitigations
  x86/speculation/mmio: Add mitigation for Processor MMIO Stale Data
  x86/speculation: Add a common function for MD_CLEAR mitigation update
  x86/speculation/mmio: Enumerate Processor MMIO Stale Data bug
  Documentation: Add documentation for Processor MMIO Stale Data

3 files changed, 283 insertions, 0 deletions

diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst
index 8cbc711cda93..4df436e7c417 100644
--- a/Documentation/admin-guide/hw-vuln/index.rst
+++ b/Documentation/admin-guide/hw-vuln/index.rst
@@ -17,3 +17,4 @@ are configurable at compile, boot or run time.
    special-register-buffer-data-sampling.rst
    core-scheduling.rst
    l1d_flush.rst
+   processor_mmio_stale_data.rst
diff --git a/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
new file mode 100644
index 000000000000..9393c50b5afc
--- /dev/null
+++ b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
@@ -0,0 +1,246 @@
+=========================================
+Processor MMIO Stale Data Vulnerabilities
+=========================================
+
+Processor MMIO Stale Data Vulnerabilities are a class of memory-mapped I/O
+(MMIO) vulnerabilities that can expose data. The sequences of operations for
+exposing data range from simple to very complex. Because most of the
+vulnerabilities require the attacker to have access to MMIO, many environments
+are not affected. System environments using virtualization where MMIO access is
+provided to untrusted guests may need mitigation. These vulnerabilities are
+not transient execution attacks. However, these vulnerabilities may propagate
+stale data into core fill buffers where the data can subsequently be inferred
+by an unmitigated transient execution attack. Mitigation for these
+vulnerabilities includes a combination of microcode update and software
+changes, depending on the platform and usage model. Some of these mitigations
+are similar to those used to mitigate Microarchitectural Data Sampling (MDS) or
+those used to mitigate Special Register Buffer Data Sampling (SRBDS).
+
+Data Propagators
+================
+Propagators are operations that result in stale data being copied or moved from
+one microarchitectural buffer or register to another. Processor MMIO Stale Data
+Vulnerabilities are operations that may result in stale data being directly
+read into an architectural, software-visible state or sampled from a buffer or
+register.
+
+Fill Buffer Stale Data Propagator (FBSDP)
+-----------------------------------------
+Stale data may propagate from fill buffers (FB) into the non-coherent portion
+of the uncore on some non-coherent writes. Fill buffer propagation by itself
+does not make stale data architecturally visible. Stale data must be propagated
+to a location where it is subject to reading or sampling.
+
+Sideband Stale Data Propagator (SSDP)
+-------------------------------------
+The sideband stale data propagator (SSDP) is limited to the client (including
+Intel Xeon server E3) uncore implementation. The sideband response buffer is
+shared by all client cores. For non-coherent reads that go to sideband
+destinations, the uncore logic returns 64 bytes of data to the core, including
+both requested data and unrequested stale data, from a transaction buffer and
+the sideband response buffer. As a result, stale data from the sideband
+response and transaction buffers may now reside in a core fill buffer.
+
+Primary Stale Data Propagator (PSDP)
+------------------------------------
+The primary stale data propagator (PSDP) is limited to the client (including
+Intel Xeon server E3) uncore implementation. Similar to the sideband response
+buffer, the primary response buffer is shared by all client cores. For some
+processors, MMIO primary reads will return 64 bytes of data to the core fill
+buffer including both requested data and unrequested stale data. This is
+similar to the sideband stale data propagator.
+
+Vulnerabilities
+===============
+Device Register Partial Write (DRPW) (CVE-2022-21166)
+-----------------------------------------------------
+Some endpoint MMIO registers incorrectly handle writes that are smaller than
+the register size. Instead of aborting the write or only copying the correct
+subset of bytes (for example, 2 bytes for a 2-byte write), more bytes than
+specified by the write transaction may be written to the register. On
+processors affected by FBSDP, this may expose stale data from the fill buffers
+of the core that created the write transaction.
+
+Shared Buffers Data Sampling (SBDS) (CVE-2022-21125)
+----------------------------------------------------
+After propagators may have moved data around the uncore and copied stale data
+into client core fill buffers, processors affected by MFBDS can leak data from
+the fill buffer. It is limited to the client (including Intel Xeon server E3)
+uncore implementation.
+
+Shared Buffers Data Read (SBDR) (CVE-2022-21123)
+------------------------------------------------
+It is similar to Shared Buffer Data Sampling (SBDS) except that the data is
+directly read into the architectural software-visible state. It is limited to
+the client (including Intel Xeon server E3) uncore implementation.
+
+Affected Processors
+===================
+Not all the CPUs are affected by all the variants. For instance, most
+processors for the server market (excluding Intel Xeon E3 processors) are
+impacted by only Device Register Partial Write (DRPW).
+
+Below is the list of affected Intel processors [#f1]_:
+
+   ===================  ============  =========
+   Common name          Family_Model  Steppings
+   ===================  ============  =========
+   HASWELL_X            06_3FH        2,4
+   SKYLAKE_L            06_4EH        3
+   BROADWELL_X          06_4FH        All
+   SKYLAKE_X            06_55H        3,4,6,7,11
+   BROADWELL_D          06_56H        3,4,5
+   SKYLAKE              06_5EH        3
+   ICELAKE_X            06_6AH        4,5,6
+   ICELAKE_D            06_6CH        1
+   ICELAKE_L            06_7EH        5
+   ATOM_TREMONT_D       06_86H        All
+   LAKEFIELD            06_8AH        1
+   KABYLAKE_L           06_8EH        9 to 12
+   ATOM_TREMONT         06_96H        1
+   ATOM_TREMONT_L       06_9CH        0
+   KABYLAKE             06_9EH        9 to 13
+   COMETLAKE            06_A5H        2,3,5
+   COMETLAKE_L          06_A6H        0,1
+   ROCKETLAKE           06_A7H        1
+   ===================  ============  =========
+
+If a CPU is in the affected processor list, but not affected by a variant, it
+is indicated by new bits in MSR IA32_ARCH_CAPABILITIES. As described in a later
+section, mitigation largely remains the same for all the variants, i.e. to
+clear the CPU fill buffers via VERW instruction.
+
+New bits in MSRs
+================
+Newer processors and microcode update on existing affected processors added new
+bits to IA32_ARCH_CAPABILITIES MSR. These bits can be used to enumerate
+specific variants of Processor MMIO Stale Data vulnerabilities and mitigation
+capability.
+
+MSR IA32_ARCH_CAPABILITIES
+--------------------------
+Bit 13 - SBDR_SSDP_NO - When set, processor is not affected by either the
+	 Shared Buffers Data Read (SBDR) vulnerability or the sideband stale
+	 data propagator (SSDP).
+Bit 14 - FBSDP_NO - When set, processor is not affected by the Fill Buffer
+	 Stale Data Propagator (FBSDP).
+Bit 15 - PSDP_NO - When set, processor is not affected by Primary Stale Data
+	 Propagator (PSDP).
+Bit 17 - FB_CLEAR - When set, VERW instruction will overwrite CPU fill buffer
+	 values as part of MD_CLEAR operations. Processors that do not
+	 enumerate MDS_NO (meaning they are affected by MDS) but that do
+	 enumerate support for both L1D_FLUSH and MD_CLEAR implicitly enumerate
+	 FB_CLEAR as part of their MD_CLEAR support.
+Bit 18 - FB_CLEAR_CTRL - Processor supports read and write to MSR
+	 IA32_MCU_OPT_CTRL[FB_CLEAR_DIS]. On such processors, the FB_CLEAR_DIS
+	 bit can be set to cause the VERW instruction to not perform the
+	 FB_CLEAR action. Not all processors that support FB_CLEAR will support
+	 FB_CLEAR_CTRL.
+
+MSR IA32_MCU_OPT_CTRL
+---------------------
+Bit 3 - FB_CLEAR_DIS - When set, VERW instruction does not perform the FB_CLEAR
+action. This may be useful to reduce the performance impact of FB_CLEAR in
+cases where system software deems it warranted (for example, when performance
+is more critical, or the untrusted software has no MMIO access). Note that
+FB_CLEAR_DIS has no impact on enumeration (for example, it does not change
+FB_CLEAR or MD_CLEAR enumeration) and it may not be supported on all processors
+that enumerate FB_CLEAR.
+
+Mitigation
+==========
+Like MDS, all variants of Processor MMIO Stale Data vulnerabilities  have the
+same mitigation strategy to force the CPU to clear the affected buffers before
+an attacker can extract the secrets.
+
+This is achieved by using the otherwise unused and obsolete VERW instruction in
+combination with a microcode update. The microcode clears the affected CPU
+buffers when the VERW instruction is executed.
+
+Kernel reuses the MDS function to invoke the buffer clearing:
+
+	mds_clear_cpu_buffers()
+
+On MDS affected CPUs, the kernel already invokes CPU buffer clear on
+kernel/userspace, hypervisor/guest and C-state (idle) transitions. No
+additional mitigation is needed on such CPUs.
+
+For CPUs not affected by MDS or TAA, mitigation is needed only for the attacker
+with MMIO capability. Therefore, VERW is not required for kernel/userspace. For
+virtualization case, VERW is only needed at VMENTER for a guest with MMIO
+capability.
+
+Mitigation points
+-----------------
+Return to user space
+^^^^^^^^^^^^^^^^^^^^
+Same mitigation as MDS when affected by MDS/TAA, otherwise no mitigation
+needed.
+
+C-State transition
+^^^^^^^^^^^^^^^^^^
+Control register writes by CPU during C-state transition can propagate data
+from fill buffer to uncore buffers. Execute VERW before C-state transition to
+clear CPU fill buffers.
+
+Guest entry point
+^^^^^^^^^^^^^^^^^
+Same mitigation as MDS when processor is also affected by MDS/TAA, otherwise
+execute VERW at VMENTER only for MMIO capable guests. On CPUs not affected by
+MDS/TAA, guest without MMIO access cannot extract secrets using Processor MMIO
+Stale Data vulnerabilities, so there is no need to execute VERW for such guests.
+
+Mitigation control on the kernel command line
+---------------------------------------------
+The kernel command line allows to control the Processor MMIO Stale Data
+mitigations at boot time with the option "mmio_stale_data=". The valid
+arguments for this option are:
+
+  ==========  =================================================================
+  full        If the CPU is vulnerable, enable mitigation; CPU buffer clearing
+              on exit to userspace and when entering a VM. Idle transitions are
+              protected as well. It does not automatically disable SMT.
+  full,nosmt  Same as full, with SMT disabled on vulnerable CPUs. This is the
+              complete mitigation.
+  off         Disables mitigation completely.
+  ==========  =================================================================
+
+If the CPU is affected and mmio_stale_data=off is not supplied on the kernel
+command line, then the kernel selects the appropriate mitigation.
+
+Mitigation status information
+-----------------------------
+The Linux kernel provides a sysfs interface to enumerate the current
+vulnerability status of the system: whether the system is vulnerable, and
+which mitigations are active. The relevant sysfs file is:
+
+	/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
+
+The possible values in this file are:
+
+  .. list-table::
+
+     * - 'Not affected'
+       - The processor is not vulnerable
+     * - 'Vulnerable'
+       - The processor is vulnerable, but no mitigation enabled
+     * - 'Vulnerable: Clear CPU buffers attempted, no microcode'
+       - The processor is vulnerable, but microcode is not updated. The
+         mitigation is enabled on a best effort basis.
+     * - 'Mitigation: Clear CPU buffers'
+       - The processor is vulnerable and the CPU buffer clearing mitigation is
+         enabled.
+
+If the processor is vulnerable then the following information is appended to
+the above information:
+
+  ========================  ===========================================
+  'SMT vulnerable'          SMT is enabled
+  'SMT disabled'            SMT is disabled
+  'SMT Host state unknown'  Kernel runs in a VM, Host SMT state unknown
+  ========================  ===========================================
+
+References
+----------
+.. [#f1] Affected Processors
+   https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 8090130b544b..bba2f27d7358 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3176,6 +3176,7 @@
 					       srbds=off [X86,INTEL]
 					       no_entry_flush [PPC]
 					       no_uaccess_flush [PPC]
+					       mmio_stale_data=off [X86]
 
 				Exceptions:
 					       This does not have any effect on
@@ -3197,6 +3198,7 @@
 				Equivalent to: l1tf=flush,nosmt [X86]
 					       mds=full,nosmt [X86]
 					       tsx_async_abort=full,nosmt [X86]
+					       mmio_stale_data=full,nosmt [X86]
 
 	mminit_loglevel=
 			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
@@ -3206,6 +3208,40 @@
 			log everything. Information is printed at KERN_DEBUG
 			so loglevel=8 may also need to be specified.
 
+	mmio_stale_data=
+			[X86,INTEL] Control mitigation for the Processor
+			MMIO Stale Data vulnerabilities.
+
+			Processor MMIO Stale Data is a class of
+			vulnerabilities that may expose data after an MMIO
+			operation. Exposed data could originate or end in
+			the same CPU buffers as affected by MDS and TAA.
+			Therefore, similar to MDS and TAA, the mitigation
+			is to clear the affected CPU buffers.
+
+			This parameter controls the mitigation. The
+			options are:
+
+			full       - Enable mitigation on vulnerable CPUs
+
+			full,nosmt - Enable mitigation and disable SMT on
+				     vulnerable CPUs.
+
+			off        - Unconditionally disable mitigation
+
+			On MDS or TAA affected machines,
+			mmio_stale_data=off can be prevented by an active
+			MDS or TAA mitigation as these vulnerabilities are
+			mitigated with the same mechanism so in order to
+			disable this mitigation, you need to specify
+			mds=off and tsx_async_abort=off too.
+
+			Not specifying this option is equivalent to
+			mmio_stale_data=full.
+
+			For details see:
+			Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
+
 	module.sig_enforce
 			[KNL] When CONFIG_MODULE_SIG is set, this means that
 			modules without (valid) signatures will fail to load.