Merge tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 retbleed fixes from Borislav Petkov:
 "Just when you thought that all the speculation bugs were addressed and
  solved and the nightmare is complete, here's the next one: speculating
  after RET instructions and leaking privileged information using the
  now pretty much classical covert channels.

  It is called RETBleed and the mitigation effort and controlling
  functionality has been modelled similar to what already existing
  mitigations provide"

* tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits)
  x86/speculation: Disable RRSBA behavior
  x86/kexec: Disable RET on kexec
  x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported
  x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry
  x86/bugs: Add Cannon lake to RETBleed affected CPU list
  x86/retbleed: Add fine grained Kconfig knobs
  x86/cpu/amd: Enumerate BTC_NO
  x86/common: Stamp out the stepping madness
  KVM: VMX: Prevent RSB underflow before vmenter
  x86/speculation: Fill RSB on vmexit for IBRS
  KVM: VMX: Fix IBRS handling after vmexit
  KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
  KVM: VMX: Convert launched argument to flags
  KVM: VMX: Flatten __vmx_vcpu_run()
  objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}
  x86/speculation: Remove x86_spec_ctrl_mask
  x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit
  x86/speculation: Fix SPEC_CTRL write on SMT state change
  x86/speculation: Fix firmware entry SPEC_CTRL handling
  x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n
  ...

Author: torvalds

Documentation/admin-guide/kernel-parameters.txt

@@ -5197,6 +5197,30 @@
 
 	retain_initrd	[RAM] Keep initrd memory after extraction
 
+	retbleed=	[X86] Control mitigation of RETBleed (Arbitrary
+			Speculative Code Execution with Return Instructions)
+			vulnerability.
+
+			off          - no mitigation
+			auto         - automatically select a migitation
+			auto,nosmt   - automatically select a mitigation,
+				       disabling SMT if necessary for
+				       the full mitigation (only on Zen1
+				       and older without STIBP).
+			ibpb	     - mitigate short speculation windows on
+				       basic block boundaries too. Safe, highest
+				       perf impact.
+			unret        - force enable untrained return thunks,
+				       only effective on AMD f15h-f17h
+				       based systems.
+			unret,nosmt  - like unret, will disable SMT when STIBP
+			               is not available.
+
+			Selecting 'auto' will choose a mitigation method at run
+			time according to the CPU.
+
+			Not specifying this option is equivalent to retbleed=auto.
+
 	rfkill.default_state=
 		0	"airplane mode".  All wifi, bluetooth, wimax, gps, fm,
 			etc. communication is blocked by default.
@@ -5568,6 +5592,7 @@
 			eibrs		  - enhanced IBRS
 			eibrs,retpoline   - enhanced IBRS + Retpolines
 			eibrs,lfence      - enhanced IBRS + LFENCE
+			ibrs		  - use IBRS to protect kernel
 
 			Not specifying this option is equivalent to
 			spectre_v2=auto.

arch/x86/Kconfig

@@ -462,29 +462,6 @@ config GOLDFISH
 	def_bool y
 	depends on X86_GOLDFISH
 
-config RETPOLINE
-	bool "Avoid speculative indirect branches in kernel"
-	select OBJTOOL if HAVE_OBJTOOL
-	default y
-	help
-	  Compile kernel with the retpoline compiler options to guard against
-	  kernel-to-user data leaks by avoiding speculative indirect
-	  branches. Requires a compiler with -mindirect-branch=thunk-extern
-	  support for full protection. The kernel may run slower.
-
-config CC_HAS_SLS
-	def_bool $(cc-option,-mharden-sls=all)
-
-config SLS
-	bool "Mitigate Straight-Line-Speculation"
-	depends on CC_HAS_SLS && X86_64
-	select OBJTOOL if HAVE_OBJTOOL
-	default n
-	help
-	  Compile the kernel with straight-line-speculation options to guard
-	  against straight line speculation. The kernel image might be slightly
-	  larger.
-
 config X86_CPU_RESCTRL
 	bool "x86 CPU resource control support"
 	depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)
@@ -2453,6 +2430,91 @@ source "kernel/livepatch/Kconfig"
 
 endmenu
 
+config CC_HAS_SLS
+	def_bool $(cc-option,-mharden-sls=all)
+
+config CC_HAS_RETURN_THUNK
+	def_bool $(cc-option,-mfunction-return=thunk-extern)
+
+menuconfig SPECULATION_MITIGATIONS
+	bool "Mitigations for speculative execution vulnerabilities"
+	default y
+	help
+	  Say Y here to enable options which enable mitigations for
+	  speculative execution hardware vulnerabilities.
+
+	  If you say N, all mitigations will be disabled. You really
+	  should know what you are doing to say so.
+
+if SPECULATION_MITIGATIONS
+
+config PAGE_TABLE_ISOLATION
+	bool "Remove the kernel mapping in user mode"
+	default y
+	depends on (X86_64 || X86_PAE)
+	help
+	  This feature reduces the number of hardware side channels by
+	  ensuring that the majority of kernel addresses are not mapped
+	  into userspace.
+
+	  See Documentation/x86/pti.rst for more details.
+
+config RETPOLINE
+	bool "Avoid speculative indirect branches in kernel"
+	select OBJTOOL if HAVE_OBJTOOL
+	default y
+	help
+	  Compile kernel with the retpoline compiler options to guard against
+	  kernel-to-user data leaks by avoiding speculative indirect
+	  branches. Requires a compiler with -mindirect-branch=thunk-extern
+	  support for full protection. The kernel may run slower.
+
+config RETHUNK
+	bool "Enable return-thunks"
+	depends on RETPOLINE && CC_HAS_RETURN_THUNK
+	select OBJTOOL if HAVE_OBJTOOL
+	default y
+	help
+	  Compile the kernel with the return-thunks compiler option to guard
+	  against kernel-to-user data leaks by avoiding return speculation.
+	  Requires a compiler with -mfunction-return=thunk-extern
+	  support for full protection. The kernel may run slower.
+
+config CPU_UNRET_ENTRY
+	bool "Enable UNRET on kernel entry"
+	depends on CPU_SUP_AMD && RETHUNK
+	default y
+	help
+	  Compile the kernel with support for the retbleed=unret mitigation.
+
+config CPU_IBPB_ENTRY
+	bool "Enable IBPB on kernel entry"
+	depends on CPU_SUP_AMD
+	default y
+	help
+	  Compile the kernel with support for the retbleed=ibpb mitigation.
+
+config CPU_IBRS_ENTRY
+	bool "Enable IBRS on kernel entry"
+	depends on CPU_SUP_INTEL
+	default y
+	help
+	  Compile the kernel with support for the spectre_v2=ibrs mitigation.
+	  This mitigates both spectre_v2 and retbleed at great cost to
+	  performance.
+
+config SLS
+	bool "Mitigate Straight-Line-Speculation"
+	depends on CC_HAS_SLS && X86_64
+	select OBJTOOL if HAVE_OBJTOOL
+	default n
+	help
+	  Compile the kernel with straight-line-speculation options to guard
+	  against straight line speculation. The kernel image might be slightly
+	  larger.
+
+endif
+
 config ARCH_HAS_ADD_PAGES
 	def_bool y
 	depends on ARCH_ENABLE_MEMORY_HOTPLUG

arch/x86/Makefile

@@ -21,6 +21,12 @@ ifdef CONFIG_CC_IS_CLANG
 RETPOLINE_CFLAGS	:= -mretpoline-external-thunk
 RETPOLINE_VDSO_CFLAGS	:= -mretpoline
 endif
+
+ifdef CONFIG_RETHUNK
+RETHUNK_CFLAGS		:= -mfunction-return=thunk-extern
+RETPOLINE_CFLAGS	+= $(RETHUNK_CFLAGS)
+endif
+
 export RETPOLINE_CFLAGS
 export RETPOLINE_VDSO_CFLAGS
 

arch/x86/entry/Makefile

@@ -11,7 +11,7 @@ CFLAGS_REMOVE_common.o		= $(CC_FLAGS_FTRACE)
 
 CFLAGS_common.o			+= -fno-stack-protector
 
-obj-y				:= entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
+obj-y				:= entry.o entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
 obj-y				+= common.o
 
 obj-y				+= vdso/

arch/x86/entry/calling.h

@@ -7,6 +7,8 @@
 #include <asm/asm-offsets.h>
 #include <asm/processor-flags.h>
 #include <asm/ptrace-abi.h>
+#include <asm/msr.h>
+#include <asm/nospec-branch.h>
 
 /*
 
@@ -282,6 +284,66 @@ For 32-bit we have the following conventions - kernel is built with
 
 #endif
 
+/*
+ * IBRS kernel mitigation for Spectre_v2.
+ *
+ * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
+ * the regs it uses (AX, CX, DX). Must be called before the first RET
+ * instruction (NOTE! UNTRAIN_RET includes a RET instruction)
+ *
+ * The optional argument is used to save/restore the current value,
+ * which is used on the paranoid paths.
+ *
+ * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
+ */
+.macro IBRS_ENTER save_reg
+#ifdef CONFIG_CPU_IBRS_ENTRY
+	ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+	movl	$MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+	rdmsr
+	shl	$32, %rdx
+	or	%rdx, %rax
+	mov	%rax, \save_reg
+	test	$SPEC_CTRL_IBRS, %eax
+	jz	.Ldo_wrmsr_\@
+	lfence
+	jmp	.Lend_\@
+.Ldo_wrmsr_\@:
+.endif
+
+	movq	PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+	movl	%edx, %eax
+	shr	$32, %rdx
+	wrmsr
+.Lend_\@:
+#endif
+.endm
+
+/*
+ * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
+ * regs. Must be called after the last RET.
+ */
+.macro IBRS_EXIT save_reg
+#ifdef CONFIG_CPU_IBRS_ENTRY
+	ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+	movl	$MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+	mov	\save_reg, %rdx
+.else
+	movq	PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+	andl	$(~SPEC_CTRL_IBRS), %edx
+.endif
+
+	movl	%edx, %eax
+	shr	$32, %rdx
+	wrmsr
+.Lend_\@:
+#endif
+.endm
+
 /*
  * Mitigate Spectre v1 for conditional swapgs code paths.
  *

arch/x86/entry/entry.S

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common place for both 32- and 64-bit entry routines.
+ */
+
+#include <linux/linkage.h>
+#include <asm/export.h>
+#include <asm/msr-index.h>
+
+.pushsection .noinstr.text, "ax"
+
+SYM_FUNC_START(entry_ibpb)
+	movl	$MSR_IA32_PRED_CMD, %ecx
+	movl	$PRED_CMD_IBPB, %eax
+	xorl	%edx, %edx
+	wrmsr
+	RET
+SYM_FUNC_END(entry_ibpb)
+/* For KVM */
+EXPORT_SYMBOL_GPL(entry_ibpb);
+
+.popsection

arch/x86/entry/entry_32.S

@@ -698,7 +698,6 @@ SYM_CODE_START(__switch_to_asm)
 	movl	%ebx, PER_CPU_VAR(__stack_chk_guard)
 #endif
 
-#ifdef CONFIG_RETPOLINE
 	/*
 	 * When switching from a shallower to a deeper call stack
 	 * the RSB may either underflow or use entries populated
@@ -707,7 +706,6 @@ SYM_CODE_START(__switch_to_asm)
 	 * speculative execution to prevent attack.
 	 */
 	FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif
 
 	/* Restore flags or the incoming task to restore AC state. */
 	popfl