Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull STIBP fallout fixes from Thomas Gleixner:
 "The performance destruction department finally got it's act together
  and came up with a cure for the STIPB regression:

   - Provide a command line option to control the spectre v2 user space
     mitigations. Default is either seccomp or prctl (if seccomp is
     disabled in Kconfig). prctl allows mitigation opt-in, seccomp
     enables the migitation for sandboxed processes.

   - Rework the code to handle the conditional STIBP/IBPB control and
     remove the now unused ptrace_may_access_sched() optimization
     attempt

   - Disable STIBP automatically when SMT is disabled

   - Optimize the switch_to() logic to avoid MSR writes and invocations
     of __switch_to_xtra().

   - Make the asynchronous speculation TIF updates synchronous to
     prevent stale mitigation state.

  As a general cleanup this also makes retpoline directly depend on
  compiler support and removes the 'minimal retpoline' option which just
  pretended to provide some form of security while providing none"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (31 commits)
  x86/speculation: Provide IBPB always command line options
  x86/speculation: Add seccomp Spectre v2 user space protection mode
  x86/speculation: Enable prctl mode for spectre_v2_user
  x86/speculation: Add prctl() control for indirect branch speculation
  x86/speculation: Prepare arch_smt_update() for PRCTL mode
  x86/speculation: Prevent stale SPEC_CTRL msr content
  x86/speculation: Split out TIF update
  ptrace: Remove unused ptrace_may_access_sched() and MODE_IBRS
  x86/speculation: Prepare for conditional IBPB in switch_mm()
  x86/speculation: Avoid __switch_to_xtra() calls
  x86/process: Consolidate and simplify switch_to_xtra() code
  x86/speculation: Prepare for per task indirect branch speculation control
  x86/speculation: Add command line control for indirect branch speculation
  x86/speculation: Unify conditional spectre v2 print functions
  x86/speculataion: Mark command line parser data __initdata
  x86/speculation: Mark string arrays const correctly
  x86/speculation: Reorder the spec_v2 code
  x86/l1tf: Show actual SMT state
  x86/speculation: Rework SMT state change
  sched/smt: Expose sched_smt_present static key
  ...

2 files changed, 63 insertions, 2 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5d6ba930d4f4..aefd358a5ca3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4199,9 +4199,13 @@
 
 	spectre_v2=	[X86] Control mitigation of Spectre variant 2
 			(indirect branch speculation) vulnerability.
+			The default operation protects the kernel from
+			user space attacks.
 
-			on   - unconditionally enable
-			off  - unconditionally disable
+			on   - unconditionally enable, implies
+			       spectre_v2_user=on
+			off  - unconditionally disable, implies
+			       spectre_v2_user=off
 			auto - kernel detects whether your CPU model is
 			       vulnerable
 
@@ -4211,6 +4215,12 @@
 			CONFIG_RETPOLINE configuration option, and the
 			compiler with which the kernel was built.
 
+			Selecting 'on' will also enable the mitigation
+			against user space to user space task attacks.
+
+			Selecting 'off' will disable both the kernel and
+			the user space protections.
+
 			Specific mitigations can also be selected manually:
 
 			retpoline	  - replace indirect branches
@@ -4220,6 +4230,48 @@
 			Not specifying this option is equivalent to
 			spectre_v2=auto.
 
+	spectre_v2_user=
+			[X86] Control mitigation of Spectre variant 2
+		        (indirect branch speculation) vulnerability between
+		        user space tasks
+
+			on	- Unconditionally enable mitigations. Is
+				  enforced by spectre_v2=on
+
+			off     - Unconditionally disable mitigations. Is
+				  enforced by spectre_v2=off
+
+			prctl   - Indirect branch speculation is enabled,
+				  but mitigation can be enabled via prctl
+				  per thread.  The mitigation control state
+				  is inherited on fork.
+
+			prctl,ibpb
+				- Like "prctl" above, but only STIBP is
+				  controlled per thread. IBPB is issued
+				  always when switching between different user
+				  space processes.
+
+			seccomp
+				- Same as "prctl" above, but all seccomp
+				  threads will enable the mitigation unless
+				  they explicitly opt out.
+
+			seccomp,ibpb
+				- Like "seccomp" above, but only STIBP is
+				  controlled per thread. IBPB is issued
+				  always when switching between different
+				  user space processes.
+
+			auto    - Kernel selects the mitigation depending on
+				  the available CPU features and vulnerability.
+
+			Default mitigation:
+			If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
+
+			Not specifying this option is equivalent to
+			spectre_v2_user=auto.
+
 	spec_store_bypass_disable=
 			[HW] Control Speculative Store Bypass (SSB) Disable mitigation
 			(Speculative Store Bypass vulnerability)
diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst
index 32f3d55c54b7..c4dbe6f7cdae 100644
--- a/Documentation/userspace-api/spec_ctrl.rst
+++ b/Documentation/userspace-api/spec_ctrl.rst
@@ -92,3 +92,12 @@ Speculation misfeature controls
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
+
+- PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes
+                        (Mitigate Spectre V2 style attacks against user processes)
+
+  Invocations:
+   * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0);
+   * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0);
+   * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0);
+   * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);