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* [MODERATED] [PATCH 1/9] TAA v2 1
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
@ 2019-10-23  8:45 ` Pawan Gupta
  2019-10-23  8:52 ` [MODERATED] [PATCH 2/9] TAA v2 2 Pawan Gupta
                   ` (7 subsequent siblings)
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23  8:45 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 1/9] x86/msr: Add the IA32_TSX_CTRL MSR

Transactional Synchronization Extensions (TSX) may be used on certain
processors as part of a speculative side channel attack.  A microcode
update for existing processors that are vulnerable to this attack will
add a new MSR - IA32_TSX_CTRL to allow the system administrator the
option to disable TSX as one of the possible mitigations.

The CPUs which get this new MSR after a microcode upgrade are the ones
which do not set MSR_IA32_ARCH_CAPABILITIES.MDS_NO (bit 5) because those
CPUs have CPUID.MD_CLEAR, i.e., the VERW implementation which clears all
CPU buffers takes care of the TAA case as well.

  [ Note that future processors that are not vulnerable will also
    support the IA32_TSX_CTRL MSR. ]

Add defines for the new IA32_TSX_CTRL MSR and its bits.

TSX has two sub-features:

1. Restricted Transactional Memory (RTM) is an explicitly-used feature
   where new instructions begin and end TSX transactions.
2. Hardware Lock Elision (HLE) is implicitly used when certain kinds of
   "old" style locks are used by software.

Bit 7 of the IA32_ARCH_CAPABILITIES indicates the presence of the
IA32_TSX_CTRL MSR.

There are two control bits in IA32_TSX_CTRL MSR:

  Bit 0: When set, it disables the Restricted Transactional Memory (RTM)
         sub-feature of TSX (will force all transactions to abort on the
	 XBEGIN instruction).

  Bit 1: When set, it disables the enumeration of the RTM and HLE feature
         (i.e. it will make CPUID(EAX=7).EBX{bit4} and
	  CPUID(EAX=7).EBX{bit11} read as 0).

The other TSX sub-feature, Hardware Lock Elision (HLE), is
unconditionally disabled by the new microcode but still enumerated
as present by CPUID(EAX=7).EBX{bit4}, unless disabled by
IA32_TSX_CTRL_MSR[1] - TSX_CTRL_CPUID_CLEAR.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/include/asm/msr-index.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 20ce682a2540..da4caf6da739 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -93,6 +93,7 @@
 						  * Microarchitectural Data
 						  * Sampling (MDS) vulnerabilities.
 						  */
+#define ARCH_CAP_TSX_CTRL_MSR		BIT(7)	/* MSR for TSX control is available. */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*
@@ -103,6 +104,10 @@
 #define MSR_IA32_BBL_CR_CTL		0x00000119
 #define MSR_IA32_BBL_CR_CTL3		0x0000011e
 
+#define MSR_IA32_TSX_CTRL		0x00000122
+#define TSX_CTRL_RTM_DISABLE		BIT(0)	/* Disable RTM feature */
+#define TSX_CTRL_CPUID_CLEAR		BIT(1)	/* Disable TSX enumeration */
+
 #define MSR_IA32_SYSENTER_CS		0x00000174
 #define MSR_IA32_SYSENTER_ESP		0x00000175
 #define MSR_IA32_SYSENTER_EIP		0x00000176
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 2/9] TAA v2 2
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
  2019-10-23  8:45 ` [MODERATED] [PATCH 1/9] TAA v2 1 Pawan Gupta
@ 2019-10-23  8:52 ` Pawan Gupta
  2019-10-28  7:36   ` Thomas Gleixner
  2019-10-23  9:01 ` [MODERATED] [PATCH 3/9] TAA v2 3 Pawan Gupta
                   ` (6 subsequent siblings)
  8 siblings, 1 reply; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23  8:52 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 2/9] x86/cpu: Add a helper function x86_read_arch_cap_msr()

Add a helper function to read the IA32_ARCH_CAPABILITIES MSR.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/kernel/cpu/common.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9ae7d1bcd4f4..897c8302d982 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1092,19 +1092,26 @@ static bool __init cpu_matches(unsigned long which)
 	return m && !!(m->driver_data & which);
 }
 
-static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
+u64 x86_read_arch_cap_msr(void)
 {
 	u64 ia32_cap = 0;
 
+	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
+		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
+
+	return ia32_cap;
+}
+
+static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
+{
+	u64 ia32_cap = x86_read_arch_cap_msr();
+
 	if (cpu_matches(NO_SPECULATION))
 		return;
 
 	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
 	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
 
-	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
-		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
-
 	if (!cpu_matches(NO_SSB) && !(ia32_cap & ARCH_CAP_SSB_NO) &&
 	   !cpu_has(c, X86_FEATURE_AMD_SSB_NO))
 		setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 3/9] TAA v2 3
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
  2019-10-23  8:45 ` [MODERATED] [PATCH 1/9] TAA v2 1 Pawan Gupta
  2019-10-23  8:52 ` [MODERATED] [PATCH 2/9] TAA v2 2 Pawan Gupta
@ 2019-10-23  9:01 ` Pawan Gupta
  2019-10-23  9:30 ` [MODERATED] [PATCH 4/9] TAA v2 4 Pawan Gupta
                   ` (5 subsequent siblings)
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23  9:01 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 3/9] x86/cpu: Add a "tsx=" cmdline option with TSX disabled by
 default

Add a kernel cmdline parameter "tsx" to control the Transactional
Synchronization Extensions (TSX) feature. On CPUs that support TSX
control, use "tsx=on|off" to enable or disable TSX. Not specifying this
option is equivalent to "tsx=off". This is because on certain processors
TSX may be used as a part of a speculative side channel attack.

Carve out the TSX controlling functionality into a separate compilation
unit because TSX is a CPU feature while the TSX async abort control
machinery will go to cpu/bugs.c.

 [ bp: - Massage, shorten and clear the arg buffer.
       - Clarifications of the tsx= possible options - Josh.
       - Expand on TSX_CTRL availability - Pawan. ]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Babu Moger <Babu.Moger@amd.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: linux-doc@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Cc: Zhao Yakui <yakui.zhao@intel.com>
---
 .../admin-guide/kernel-parameters.txt         |  26 ++++
 arch/x86/kernel/cpu/Makefile                  |   2 +-
 arch/x86/kernel/cpu/common.c                  |   2 +
 arch/x86/kernel/cpu/cpu.h                     |  18 +++
 arch/x86/kernel/cpu/intel.c                   |   5 +
 arch/x86/kernel/cpu/tsx.c                     | 125 ++++++++++++++++++
 6 files changed, 177 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/kernel/cpu/tsx.c

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a84a83f8881e..af4b1d95b08f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4848,6 +4848,32 @@
 			interruptions from clocksource watchdog are not
 			acceptable).
 
+	tsx=		[X86] Control Transactional Synchronization
+			Extensions (TSX) feature in Intel processors that
+			support TSX control.
+
+			This parameter controls the TSX feature. The options are:
+
+			on	- Enable TSX on the system. Although there are
+				mitigations for all known security vulnerabilities,
+				TSX has been known to be an accelerator for
+				several previous speculation-related CVEs, and
+				so there may be unknown	security risks associated
+				with leaving it enabled.
+
+			off	- Disable TSX on the system. (Note that this
+				option takes effect only on newer CPUs which are
+				not vulnerable to MDS, i.e., have
+				MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
+				the new IA32_TSX_CTRL MSR through a microcode
+				update. This new MSR allows for the reliable
+				deactivation of the TSX functionality.)
+
+			Not specifying this option is equivalent to tsx=off.
+
+			See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
+			for more details.
+
 	turbografx.map[2|3]=	[HW,JOY]
 			TurboGraFX parallel port interface
 			Format:
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index d7a1e5a9331c..890f60083eca 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -30,7 +30,7 @@ obj-$(CONFIG_PROC_FS)	+= proc.o
 obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
 
 ifdef CONFIG_CPU_SUP_INTEL
-obj-y			+= intel.o intel_pconfig.o
+obj-y			+= intel.o intel_pconfig.o tsx.o
 obj-$(CONFIG_PM)	+= intel_epb.o
 endif
 obj-$(CONFIG_CPU_SUP_AMD)		+= amd.o
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 897c8302d982..885d4ac2111a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1561,6 +1561,8 @@ void __init identify_boot_cpu(void)
 #endif
 	cpu_detect_tlb(&boot_cpu_data);
 	setup_cr_pinning();
+
+	tsx_init();
 }
 
 void identify_secondary_cpu(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index c0e2407abdd6..38ab6e115eac 100644
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -44,6 +44,22 @@ struct _tlb_table {
 extern const struct cpu_dev *const __x86_cpu_dev_start[],
 			    *const __x86_cpu_dev_end[];
 
+#ifdef CONFIG_CPU_SUP_INTEL
+enum tsx_ctrl_states {
+	TSX_CTRL_ENABLE,
+	TSX_CTRL_DISABLE,
+	TSX_CTRL_NOT_SUPPORTED,
+};
+
+extern __ro_after_init enum tsx_ctrl_states tsx_ctrl_state;
+
+extern void __init tsx_init(void);
+extern void tsx_enable(void);
+extern void tsx_disable(void);
+#else
+static inline void tsx_init(void) { }
+#endif /* CONFIG_CPU_SUP_INTEL */
+
 extern void get_cpu_cap(struct cpuinfo_x86 *c);
 extern void get_cpu_address_sizes(struct cpuinfo_x86 *c);
 extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c);
@@ -62,4 +78,6 @@ unsigned int aperfmperf_get_khz(int cpu);
 
 extern void x86_spec_ctrl_setup_ap(void);
 
+extern u64 x86_read_arch_cap_msr(void);
+
 #endif /* ARCH_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index c2fdc00df163..11d5c5950e2d 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -762,6 +762,11 @@ static void init_intel(struct cpuinfo_x86 *c)
 		detect_tme(c);
 
 	init_intel_misc_features(c);
+
+	if (tsx_ctrl_state == TSX_CTRL_ENABLE)
+		tsx_enable();
+	if (tsx_ctrl_state == TSX_CTRL_DISABLE)
+		tsx_disable();
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
new file mode 100644
index 000000000000..04471c4378d8
--- /dev/null
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel Transactional Synchronization Extensions (TSX) control.
+ *
+ * Copyright (C) 2019 Intel Corporation
+ *
+ * Author:
+ *	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+ */
+
+#include <linux/cpufeature.h>
+
+#include <asm/cmdline.h>
+
+#include "cpu.h"
+
+enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
+
+void tsx_disable(void)
+{
+	u64 tsx;
+
+	rdmsrl(MSR_IA32_TSX_CTRL, tsx);
+
+	/* Force all transactions to immediately abort */
+	tsx |= TSX_CTRL_RTM_DISABLE;
+
+	/*
+	 * Ensure TSX support is not enumerated in CPUID.
+	 * This is visible to userspace and will ensure they
+	 * do not waste resources trying TSX transactions that
+	 * will always abort.
+	 */
+	tsx |= TSX_CTRL_CPUID_CLEAR;
+
+	wrmsrl(MSR_IA32_TSX_CTRL, tsx);
+}
+
+void tsx_enable(void)
+{
+	u64 tsx;
+
+	rdmsrl(MSR_IA32_TSX_CTRL, tsx);
+
+	/* Enable the RTM feature in the cpu */
+	tsx &= ~TSX_CTRL_RTM_DISABLE;
+
+	/*
+	 * Ensure TSX support is enumerated in CPUID.
+	 * This is visible to userspace and will ensure they
+	 * can enumerate and use the TSX feature.
+	 */
+	tsx &= ~TSX_CTRL_CPUID_CLEAR;
+
+	wrmsrl(MSR_IA32_TSX_CTRL, tsx);
+}
+
+static bool __init tsx_ctrl_is_supported(void)
+{
+	u64 ia32_cap = x86_read_arch_cap_msr();
+
+	/*
+	 * TSX is controlled via MSR_IA32_TSX_CTRL.  However, support for this
+	 * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
+	 *
+	 * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
+	 * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
+	 * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
+	 * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
+	 * tsx= cmdline requests will do nothing on CPUs without
+	 * MSR_IA32_TSX_CTRL support.
+	 */
+	return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
+}
+
+void __init tsx_init(void)
+{
+	char arg[4] = {};
+	int ret;
+
+	if (!tsx_ctrl_is_supported())
+		return;
+
+	ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
+	if (ret >= 0) {
+		if (!strcmp(arg, "on")) {
+			tsx_ctrl_state = TSX_CTRL_ENABLE;
+		} else if (!strcmp(arg, "off")) {
+			tsx_ctrl_state = TSX_CTRL_DISABLE;
+		} else {
+			tsx_ctrl_state = TSX_CTRL_DISABLE;
+			pr_err("tsx: invalid option, defaulting to off\n");
+		}
+	} else {
+		/* tsx= not provided, defaulting to off */
+		tsx_ctrl_state = TSX_CTRL_DISABLE;
+	}
+
+	if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
+		tsx_disable();
+
+		/*
+		 * tsx_disable() will change the state of the
+		 * RTM CPUID bit.  Clear it here since it is now
+		 * expected to be not set.
+		 */
+		setup_clear_cpu_cap(X86_FEATURE_RTM);
+	} else if (tsx_ctrl_state == TSX_CTRL_ENABLE) {
+
+		/*
+		 * HW defaults TSX to be enabled at bootup.
+		 * We may still need the TSX enable support
+		 * during init for special cases like
+		 * kexec after TSX is disabled.
+		 */
+		tsx_enable();
+
+		/*
+		 * tsx_enable() will change the state of the
+		 * RTM CPUID bit.  Force it here since it is now
+		 * expected to be set.
+		 */
+		setup_force_cpu_cap(X86_FEATURE_RTM);
+	}
+}
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 4/9] TAA v2 4
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (2 preceding siblings ...)
  2019-10-23  9:01 ` [MODERATED] [PATCH 3/9] TAA v2 3 Pawan Gupta
@ 2019-10-23  9:30 ` Pawan Gupta
  2019-10-23 10:19 ` [MODERATED] [PATCH 5/9] TAA v2 5 Pawan Gupta
                   ` (4 subsequent siblings)
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23  9:30 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 4/9] x86/speculation/taa: Add mitigation for TSX Async Abort

TSX Async Abort (TAA) is a side channel vulnerability to the internal
buffers in some Intel processors similar to Microachitectural Data
Sampling (MDS). In this case, certain loads may speculatively pass
invalid data to dependent operations when an asynchronous abort
condition is pending in a TSX transaction.

This includes loads with no fault or assist condition. Such loads may
speculatively expose stale data from the uarch data structures as in
MDS. Scope of exposure is within the same-thread and cross-thread. This
issue affects all current processors that support TSX, but do not have
ARCH_CAP_TAA_NO (bit 8) set in MSR_IA32_ARCH_CAPABILITIES.

On CPUs which have their IA32_ARCH_CAPABILITIES MSR bit MDS_NO=0,
CPUID.MD_CLEAR=1 and the MDS mitigation is clearing the CPU buffers
using VERW or L1D_FLUSH, there is no additional mitigation needed for
TAA. On affected CPUs with MDS_NO=1 this issue can be mitigated by
disabling the Transactional Synchronization Extensions (TSX) feature.

A new MSR IA32_TSX_CTRL in future and current processors after a
microcode update can be used to control the TSX feature. There are two
bits in that MSR:

* TSX_CTRL_RTM_DISABLE disables the TSX sub-feature Restricted
Transactional Memory (RTM).

* TSX_CTRL_CPUID_CLEAR clears the RTM enumeration in CPUID. The other
TSX sub-feature, Hardware Lock Elision (HLE), is unconditionally
disabled with updated microcode but still enumerated as present by
CPUID(EAX=7).EBX{bit4}.

The second mitigation approach is similar to MDS which is clearing the
affected CPU buffers on return to user space and when entering a guest.
Relevant microcode update is required for the mitigation to work.  More
details on this approach can be found here:

  https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html

The TSX feature can be controlled by the "tsx" command line parameter.
If it is force-enabled then "Clear CPU buffers" (MDS mitigation) is
deployed. The effective mitigation state can be read from sysfs.

 [ bp:
   - massage + comments cleanup
   - s/TAA_MITIGATION_TSX_DISABLE/TAA_MITIGATION_TSX_DISABLED/g - Josh.
   - remove partial TAA mitigation in update_mds_branch_idle() - Josh.
   - s/tsx_async_abort_cmdline/tsx_async_abort_parse_cmdline/g
 ]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/include/asm/cpufeatures.h   |   1 +
 arch/x86/include/asm/msr-index.h     |   4 +
 arch/x86/include/asm/nospec-branch.h |   4 +-
 arch/x86/include/asm/processor.h     |   7 ++
 arch/x86/kernel/cpu/bugs.c           | 108 +++++++++++++++++++++++++++
 arch/x86/kernel/cpu/common.c         |  15 ++++
 6 files changed, 137 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 0652d3eed9bd..989e03544f18 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -399,5 +399,6 @@
 #define X86_BUG_MDS			X86_BUG(19) /* CPU is affected by Microarchitectural data sampling */
 #define X86_BUG_MSBDS_ONLY		X86_BUG(20) /* CPU is only affected by the  MSDBS variant of BUG_MDS */
 #define X86_BUG_SWAPGS			X86_BUG(21) /* CPU is affected by speculation through SWAPGS */
+#define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
 
 #endif /* _ASM_X86_CPUFEATURES_H */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index da4caf6da739..b3a8bb2af0b6 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -94,6 +94,10 @@
 						  * Sampling (MDS) vulnerabilities.
 						  */
 #define ARCH_CAP_TSX_CTRL_MSR		BIT(7)	/* MSR for TSX control is available. */
+#define ARCH_CAP_TAA_NO			BIT(8)	/*
+						 * Not susceptible to
+						 * TSX Async Abort (TAA) vulnerabilities.
+						 */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 80bc209c0708..5c24a7b35166 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -314,7 +314,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
 #include <asm/segment.h>
 
 /**
- * mds_clear_cpu_buffers - Mitigation for MDS vulnerability
+ * mds_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability
  *
  * This uses the otherwise unused and obsolete VERW instruction in
  * combination with microcode which triggers a CPU buffer flush when the
@@ -337,7 +337,7 @@ static inline void mds_clear_cpu_buffers(void)
 }
 
 /**
- * mds_user_clear_cpu_buffers - Mitigation for MDS vulnerability
+ * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability
  *
  * Clear CPU buffers if the corresponding static key is enabled
  */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 6e0a3b43d027..54f5d54280f6 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -988,4 +988,11 @@ enum mds_mitigations {
 	MDS_MITIGATION_VMWERV,
 };
 
+enum taa_mitigations {
+	TAA_MITIGATION_OFF,
+	TAA_MITIGATION_UCODE_NEEDED,
+	TAA_MITIGATION_VERW,
+	TAA_MITIGATION_TSX_DISABLED,
+};
+
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 91c2561b905f..58fe3746e333 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -39,6 +39,7 @@ static void __init spectre_v2_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
+static void __init taa_select_mitigation(void);
 
 /* The base value of the SPEC_CTRL MSR that always has to be preserved. */
 u64 x86_spec_ctrl_base;
@@ -105,6 +106,7 @@ void __init check_bugs(void)
 	ssb_select_mitigation();
 	l1tf_select_mitigation();
 	mds_select_mitigation();
+	taa_select_mitigation();
 
 	arch_smt_update();
 
@@ -268,6 +270,100 @@ static int __init mds_cmdline(char *str)
 }
 early_param("mds", mds_cmdline);
 
+#undef pr_fmt
+#define pr_fmt(fmt)	"TAA: " fmt
+
+/* Default mitigation for TAA-affected CPUs */
+static enum taa_mitigations taa_mitigation __ro_after_init = TAA_MITIGATION_VERW;
+static bool taa_nosmt __ro_after_init;
+
+static const char * const taa_strings[] = {
+	[TAA_MITIGATION_OFF]		= "Vulnerable",
+	[TAA_MITIGATION_UCODE_NEEDED]	= "Vulnerable: Clear CPU buffers attempted, no microcode",
+	[TAA_MITIGATION_VERW]		= "Mitigation: Clear CPU buffers",
+	[TAA_MITIGATION_TSX_DISABLED]	= "Mitigation: TSX disabled",
+};
+
+static void __init taa_select_mitigation(void)
+{
+	u64 ia32_cap;
+
+	if (!boot_cpu_has_bug(X86_BUG_TAA)) {
+		taa_mitigation = TAA_MITIGATION_OFF;
+		return;
+	}
+
+	/* TSX previously disabled by tsx=off */
+	if (!boot_cpu_has(X86_FEATURE_RTM)) {
+		taa_mitigation = TAA_MITIGATION_TSX_DISABLED;
+		goto out;
+	}
+
+	if (cpu_mitigations_off()) {
+		taa_mitigation = TAA_MITIGATION_OFF;
+		return;
+	}
+
+	/* TAA mitigation is turned off on the cmdline (tsx_async_abort=off) */
+	if (taa_mitigation == TAA_MITIGATION_OFF)
+		goto out;
+
+	if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
+		taa_mitigation = TAA_MITIGATION_VERW;
+	else
+		taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
+
+	/*
+	 * VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1.
+	 * A microcode update fixes this behavior to clear CPU buffers. It also
+	 * adds support for MSR_IA32_TSX_CTRL which is enumerated by the
+	 * ARCH_CAP_TSX_CTRL_MSR bit.
+	 *
+	 * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode
+	 * update is required.
+	 */
+	ia32_cap = x86_read_arch_cap_msr();
+	if ( (ia32_cap & ARCH_CAP_MDS_NO) &&
+	    !(ia32_cap & ARCH_CAP_TSX_CTRL_MSR))
+		taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
+
+	/*
+	 * TSX is enabled, select alternate mitigation for TAA which is
+	 * the same as MDS. Enable MDS static branch to clear CPU buffers.
+	 *
+	 * For guests that can't determine whether the correct microcode is
+	 * present on host, enable the mitigation for UCODE_NEEDED as well.
+	 */
+	static_branch_enable(&mds_user_clear);
+
+	if (taa_nosmt || cpu_mitigations_auto_nosmt())
+		cpu_smt_disable(false);
+
+out:
+	pr_info("%s\n", taa_strings[taa_mitigation]);
+}
+
+static int __init tsx_async_abort_parse_cmdline(char *str)
+{
+	if (!boot_cpu_has_bug(X86_BUG_TAA))
+		return 0;
+
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "off")) {
+		taa_mitigation = TAA_MITIGATION_OFF;
+	} else if (!strcmp(str, "full")) {
+		taa_mitigation = TAA_MITIGATION_VERW;
+	} else if (!strcmp(str, "full,nosmt")) {
+		taa_mitigation = TAA_MITIGATION_VERW;
+		taa_nosmt = true;
+	}
+
+	return 0;
+}
+early_param("tsx_async_abort", tsx_async_abort_parse_cmdline);
+
 #undef pr_fmt
 #define pr_fmt(fmt)     "Spectre V1 : " fmt
 
@@ -786,6 +882,7 @@ static void update_mds_branch_idle(void)
 }
 
 #define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n"
+#define TAA_MSG_SMT "TAA CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html for more details.\n"
 
 void cpu_bugs_smt_update(void)
 {
@@ -819,6 +916,17 @@ void cpu_bugs_smt_update(void)
 		break;
 	}
 
+	switch (taa_mitigation) {
+	case TAA_MITIGATION_VERW:
+	case TAA_MITIGATION_UCODE_NEEDED:
+		if (sched_smt_active())
+			pr_warn_once(TAA_MSG_SMT);
+		break;
+	case TAA_MITIGATION_TSX_DISABLED:
+	case TAA_MITIGATION_OFF:
+		break;
+	}
+
 	mutex_unlock(&spec_ctrl_mutex);
 }
 
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 885d4ac2111a..f8b8afc8f5b5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1128,6 +1128,21 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	if (!cpu_matches(NO_SWAPGS))
 		setup_force_cpu_bug(X86_BUG_SWAPGS);
 
+	/*
+	 * When the CPU is not mitigated for TAA (TAA_NO=0) set TAA bug when:
+	 *	- TSX is supported or
+	 *	- TSX_CTRL is present
+	 *
+	 * TSX_CTRL check is needed for cases when TSX could be disabled before
+	 * the kernel boot e.g. kexec.
+	 * TSX_CTRL check alone is not sufficient for cases when the microcode
+	 * update is not present or running as guest that don't get TSX_CTRL.
+	 */
+	if (!(ia32_cap & ARCH_CAP_TAA_NO) &&
+	    (cpu_has(c, X86_FEATURE_RTM) ||
+	     (ia32_cap & ARCH_CAP_TSX_CTRL_MSR)))
+		setup_force_cpu_bug(X86_BUG_TAA);
+
 	if (cpu_matches(NO_MELTDOWN))
 		return;
 
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 5/9] TAA v2 5
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (3 preceding siblings ...)
  2019-10-23  9:30 ` [MODERATED] [PATCH 4/9] TAA v2 4 Pawan Gupta
@ 2019-10-23 10:19 ` Pawan Gupta
  2019-10-23 10:23 ` [MODERATED] [PATCH 6/9] TAA v2 6 Pawan Gupta
                   ` (3 subsequent siblings)
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23 10:19 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 5/9] x86/speculation/taa: Add sysfs reporting for TSX Async
 Abort

Add the sysfs reporting file for TSX Async Abort. It exposes the
vulnerability and the mitigation state similar to the existing files for
the other hardware vulnerabilities.

Sysfs file path is:
/sys/devices/system/cpu/vulnerabilities/tsx_async_abort

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/kernel/cpu/bugs.c | 23 +++++++++++++++++++++++
 drivers/base/cpu.c         |  9 +++++++++
 include/linux/cpu.h        |  3 +++
 3 files changed, 35 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 58fe3746e333..43c647e19439 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1436,6 +1436,21 @@ static ssize_t mds_show_state(char *buf)
 		       sched_smt_active() ? "vulnerable" : "disabled");
 }
 
+static ssize_t tsx_async_abort_show_state(char *buf)
+{
+	if ((taa_mitigation == TAA_MITIGATION_TSX_DISABLED) ||
+	    (taa_mitigation == TAA_MITIGATION_OFF))
+		return sprintf(buf, "%s\n", taa_strings[taa_mitigation]);
+
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
+		return sprintf(buf, "%s; SMT Host state unknown\n",
+			       taa_strings[taa_mitigation]);
+	}
+
+	return sprintf(buf, "%s; SMT %s\n", taa_strings[taa_mitigation],
+		       sched_smt_active() ? "vulnerable" : "disabled");
+}
+
 static char *stibp_state(void)
 {
 	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
@@ -1506,6 +1521,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 	case X86_BUG_MDS:
 		return mds_show_state(buf);
 
+	case X86_BUG_TAA:
+		return tsx_async_abort_show_state(buf);
+
 	default:
 		break;
 	}
@@ -1542,4 +1560,9 @@ ssize_t cpu_show_mds(struct device *dev, struct device_attribute *attr, char *bu
 {
 	return cpu_show_common(dev, attr, buf, X86_BUG_MDS);
 }
+
+ssize_t cpu_show_tsx_async_abort(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return cpu_show_common(dev, attr, buf, X86_BUG_TAA);
+}
 #endif
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index cc37511de866..0fccd8c0312e 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -554,12 +554,20 @@ ssize_t __weak cpu_show_mds(struct device *dev,
 	return sprintf(buf, "Not affected\n");
 }
 
+ssize_t __weak cpu_show_tsx_async_abort(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
 static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
 static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
 static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
 static DEVICE_ATTR(spec_store_bypass, 0444, cpu_show_spec_store_bypass, NULL);
 static DEVICE_ATTR(l1tf, 0444, cpu_show_l1tf, NULL);
 static DEVICE_ATTR(mds, 0444, cpu_show_mds, NULL);
+static DEVICE_ATTR(tsx_async_abort, 0444, cpu_show_tsx_async_abort, NULL);
 
 static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_meltdown.attr,
@@ -568,6 +576,7 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_spec_store_bypass.attr,
 	&dev_attr_l1tf.attr,
 	&dev_attr_mds.attr,
+	&dev_attr_tsx_async_abort.attr,
 	NULL
 };
 
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index d0633ebdaa9c..f35369f79771 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -59,6 +59,9 @@ extern ssize_t cpu_show_l1tf(struct device *dev,
 			     struct device_attribute *attr, char *buf);
 extern ssize_t cpu_show_mds(struct device *dev,
 			    struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_tsx_async_abort(struct device *dev,
+					struct device_attribute *attr,
+					char *buf);
 
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 6/9] TAA v2 6
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (4 preceding siblings ...)
  2019-10-23 10:19 ` [MODERATED] [PATCH 5/9] TAA v2 5 Pawan Gupta
@ 2019-10-23 10:23 ` Pawan Gupta
  2019-10-23 10:28 ` [MODERATED] [PATCH 7/9] TAA v2 7 Pawan Gupta
                   ` (2 subsequent siblings)
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23 10:23 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 6/9] kvm/x86: Export MDS_NO=0 to guests when TSX is enabled

Export the IA32_ARCH_CAPABILITIES MSR bit MDS_NO=0 to guests on TSX
Async Abort(TAA) affected hosts that have TSX enabled and updated
microcode. This is required so that the guests don't complain,

  "Vulnerable: Clear CPU buffers attempted, no microcode"

when the host has the updated microcode to clear CPU buffers.

Microcode update also adds support for MSR_IA32_TSX_CTRL which is
enumerated by the ARCH_CAP_TSX_CTRL bit in IA32_ARCH_CAPABILITIES MSR.
Guests can't do this check themselves when the ARCH_CAP_TSX_CTRL bit is
not exported to the guests.

In this case export MDS_NO=0 to the guests. When guests have
CPUID.MD_CLEAR=1, they deploy MDS mitigation which also mitigates TAA.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krcmar" <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/kvm/x86.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 661e2bf38526..fb8d80caf642 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1299,6 +1299,25 @@ static u64 kvm_get_arch_capabilities(void)
 	if (!boot_cpu_has_bug(X86_BUG_MDS))
 		data |= ARCH_CAP_MDS_NO;
 
+	/*
+	 * On TAA affected systems, export MDS_NO=0 when:
+	 *	- TSX is enabled on the host, i.e. X86_FEATURE_RTM=1.
+	 *	- Updated microcode is present. This is detected by
+	 *	  the presence of ARCH_CAP_TSX_CTRL_MSR and ensures
+	 *	  that VERW clears CPU buffers.
+	 *
+	 * When MDS_NO=0 is exported, guests deploy clear CPU buffer
+	 * mitigation and don't complain:
+	 *
+	 *	"Vulnerable: Clear CPU buffers attempted, no microcode"
+	 *
+	 * If TSX is disabled on the system, guests are also mitigated against
+	 * TAA and clear CPU buffer mitigation is not required for guests.
+	 */
+	if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) &&
+	    (data & ARCH_CAP_TSX_CTRL_MSR))
+		data &= ~ARCH_CAP_MDS_NO;
+
 	return data;
 }
 
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 7/9] TAA v2 7
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (5 preceding siblings ...)
  2019-10-23 10:23 ` [MODERATED] [PATCH 6/9] TAA v2 6 Pawan Gupta
@ 2019-10-23 10:28 ` Pawan Gupta
  2019-10-23 10:32 ` [MODERATED] [PATCH 8/9] TAA v2 8 Pawan Gupta
  2019-10-23 10:35 ` [MODERATED] [PATCH 9/9] TAA v2 9 Michal Hocko
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23 10:28 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 7/9] x86/tsx: Add "auto" option to the tsx= cmdline parameter

Platforms which are not affected by X86_BUG_TAA may want the TSX feature
enabled. Add "auto" option to the TSX cmdline parameter. When tsx=auto
disable TSX when X86_BUG_TAA is present, otherwise enable TSX.

More details on X86_BUG_TAA can be found here:
https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html

 [ bp: Extend the arg buffer to accommodate "auto\0". ]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juergen Gross <jgross@suse.com>
Cc: linux-doc@vger.kernel.org
Cc: Mark Gross <mgross@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/x86/kernel/cpu/tsx.c                       | 7 ++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index af4b1d95b08f..6e548cddb6c3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4869,6 +4869,9 @@
 				update. This new MSR allows for the reliable
 				deactivation of the TSX functionality.)
 
+			auto	- Disable TSX if X86_BUG_TAA is present,
+				  otherwise enable TSX on the system.
+
 			Not specifying this option is equivalent to tsx=off.
 
 			See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index 04471c4378d8..dda328ec2ba1 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -75,7 +75,7 @@ static bool __init tsx_ctrl_is_supported(void)
 
 void __init tsx_init(void)
 {
-	char arg[4] = {};
+	char arg[5] = {};
 	int ret;
 
 	if (!tsx_ctrl_is_supported())
@@ -87,6 +87,11 @@ void __init tsx_init(void)
 			tsx_ctrl_state = TSX_CTRL_ENABLE;
 		} else if (!strcmp(arg, "off")) {
 			tsx_ctrl_state = TSX_CTRL_DISABLE;
+		} else if (!strcmp(arg, "auto")) {
+			if (boot_cpu_has_bug(X86_BUG_TAA))
+				tsx_ctrl_state = TSX_CTRL_DISABLE;
+			else
+				tsx_ctrl_state = TSX_CTRL_ENABLE;
 		} else {
 			tsx_ctrl_state = TSX_CTRL_DISABLE;
 			pr_err("tsx: invalid option, defaulting to off\n");
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 8/9] TAA v2 8
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (6 preceding siblings ...)
  2019-10-23 10:28 ` [MODERATED] [PATCH 7/9] TAA v2 7 Pawan Gupta
@ 2019-10-23 10:32 ` Pawan Gupta
  2019-10-23 10:35 ` [MODERATED] [PATCH 9/9] TAA v2 9 Michal Hocko
  8 siblings, 0 replies; 11+ messages in thread
From: Pawan Gupta @ 2019-10-23 10:32 UTC (permalink / raw)
  To: speck

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 8/9] x86/speculation/taa: Add documentation for TSX Async
 Abort

Add the documenation for TSX Async Abort. Include the description of
the issue, how to check the mitigation state, control the mitigation,
guidance for system administrators.

 [ bp: Add proper SPDX tags, touch ups by Josh and me. ]

Co-developed-by: Antonio Gomez Iglesias <antonio.gomez.iglesias@intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Antonio Gomez Iglesias <antonio.gomez.iglesias@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juergen Gross <jgross@suse.com>
Cc: linux-doc@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
---
 .../ABI/testing/sysfs-devices-system-cpu      |   1 +
 Documentation/admin-guide/hw-vuln/index.rst   |   1 +
 .../admin-guide/hw-vuln/tsx_async_abort.rst   | 276 ++++++++++++++++++
 .../admin-guide/kernel-parameters.txt         |  38 +++
 Documentation/x86/index.rst                   |   1 +
 Documentation/x86/tsx_async_abort.rst         | 117 ++++++++
 6 files changed, 434 insertions(+)
 create mode 100644 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
 create mode 100644 Documentation/x86/tsx_async_abort.rst

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 06d0931119cc..0e77569bd5e0 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -486,6 +486,7 @@ What:		/sys/devices/system/cpu/vulnerabilities
 		/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
 		/sys/devices/system/cpu/vulnerabilities/l1tf
 		/sys/devices/system/cpu/vulnerabilities/mds
+		/sys/devices/system/cpu/vulnerabilities/tsx_async_abort
 Date:		January 2018
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
 Description:	Information about CPU vulnerabilities
diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst
index 49311f3da6f2..0802b1c67452 100644
--- a/Documentation/admin-guide/hw-vuln/index.rst
+++ b/Documentation/admin-guide/hw-vuln/index.rst
@@ -12,3 +12,4 @@ are configurable at compile, boot or run time.
    spectre
    l1tf
    mds
+   tsx_async_abort
diff --git a/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst b/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
new file mode 100644
index 000000000000..cfbb67a2e046
--- /dev/null
+++ b/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
@@ -0,0 +1,276 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+TAA - TSX Asynchronous Abort
+======================================
+
+TAA is a hardware vulnerability that allows unprivileged speculative access to
+data which is available in various CPU internal buffers by using asynchronous
+aborts within an Intel TSX transactional region.
+
+Affected processors
+-------------------
+
+This vulnerability only affects Intel processors that support Intel
+Transactional Synchronization Extensions (TSX) when the TAA_NO bit (bit 8)
+is 0 in the IA32_ARCH_CAPABILITIES MSR.  On processors where the MDS_NO bit
+(bit 5) is 0 in the IA32_ARCH_CAPABILITIES MSR, the existing MDS mitigations
+also mitigate against TAA.
+
+Whether a processor is affected or not can be read out from the TAA
+vulnerability file in sysfs. See :ref:`tsx_async_abort_sys_info`.
+
+Related CVEs
+------------
+
+The following CVE entry is related to this TAA issue:
+
+   ==============  =====  ===================================================
+   CVE-2019-11135  TAA    TSX Asynchronous Abort (TAA) condition on some
+                          microprocessors utilizing speculative execution may
+                          allow an authenticated user to potentially enable
+                          information disclosure via a side channel with
+                          local access.
+   ==============  =====  ===================================================
+
+Problem
+-------
+
+When performing store, load or L1 refill operations, processors write
+data into temporary microarchitectural structures (buffers). The data in
+those buffers can be forwarded to load operations as an optimization.
+
+Intel TSX is an extension to the x86 instruction set architecture that adds
+hardware transactional memory support to improve performance of multi-threaded
+software. TSX lets the processor expose and exploit concurrency hidden in an
+application due to dynamically avoiding unnecessary synchronization.
+
+TSX supports atomic memory transactions that are either committed (success) or
+aborted. During an abort, operations that happened within the transactional region
+are rolled back. An asynchronous abort takes place, among other options, when a
+different thread accesses a cache line that is also used within the transactional
+region when that access might lead to a data race.
+
+Immediately after an uncompleted asynchronous abort, certain speculatively
+executed loads may read data from those internal buffers and pass it to dependent
+operations. This can be then used to infer the value via a cache side channel
+attack.
+
+Because the buffers are potentially shared between Hyper-Threads cross
+Hyper-Thread attacks are possible.
+
+The victim of a malicious actor does not need to make use of TSX. Only the
+attacker needs to begin a TSX transaction and raise an asynchronous abort
+to try to leak some of data stored in the buffers.
+
+More detailed technical information is available in the TAA specific x86
+architecture section: :ref:`Documentation/x86/tsx_async_abort.rst <tsx_async_abort>`.
+
+
+Attack scenarios
+----------------
+
+Attacks against the TAA vulnerability can be implemented from unprivileged
+applications running on hosts or guests.
+
+As for MDS, the attacker has no control over the memory addresses that can be
+leaked. Only the victim is responsible for bringing data to the CPU. As a
+result, the malicious actor has to first sample as much data as possible and
+then postprocess it to try to infer any useful information from it.
+
+A potential attacker only has read access to the data. Also, there is no direct
+privilege escalation by using this technique.
+
+
+.. _tsx_async_abort_sys_info:
+
+TAA system information
+-----------------------
+
+The Linux kernel provides a sysfs interface to enumerate the current TAA status
+of mitigated systems. The relevant sysfs file is:
+
+/sys/devices/system/cpu/vulnerabilities/tsx_async_abort
+
+The possible values in this file are:
+
+.. list-table::
+
+   * - 'Vulnerable'
+     - The CPU is affected by this vulnerability and the microcode and kernel mitigation are not applied.
+   * - 'Vulnerable: Clear CPU buffers attempted, no microcode'
+     - The system tries to clear the buffers but the microcode might not support the operation.
+   * - 'Mitigation: Clear CPU buffers'
+     - The microcode has been updated to clear the buffers. TSX is still enabled.
+   * - 'Mitigation: TSX disabled'
+     - TSX is disabled.
+   * - 'Not affected'
+     - The CPU is not affected by this issue.
+
+.. _ucode_needed:
+
+Best effort mitigation mode
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If the processor is vulnerable, but the availability of the microcode-based
+mitigation mechanism is not advertised via CPUID the kernel selects a best
+effort mitigation mode.  This mode invokes the mitigation instructions
+without a guarantee that they clear the CPU buffers.
+
+This is done to address virtualization scenarios where the host has the
+microcode update applied, but the hypervisor is not yet updated to expose the
+CPUID to the guest. If the host has updated microcode the protection takes
+effect; otherwise a few CPU cycles are wasted pointlessly.
+
+The state in the tsx_async_abort sysfs file reflects this situation
+accordingly.
+
+
+Mitigation mechanism
+--------------------
+
+The kernel detects the affected CPUs and the presence of the microcode which is
+required. If a CPU is affected and the microcode is available, then the kernel
+enables the mitigation by default.
+
+
+The mitigation can be controlled at boot time via a kernel command line option.
+See :ref:`taa_mitigation_control_command_line`.
+
+.. _virt_mechanism:
+
+Virtualization mitigation
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Affected systems where the host has TAA microcode and TAA is mitigated
+by having disabled TSX previously, are not vulnerable regardless of the
+status of the VMs.
+
+In all other cases, if the host either does not have the TAA microcode or the
+kernel is not mitigated, the system might be vulnerable.
+
+
+.. _taa_mitigation_control_command_line:
+
+Mitigation control on the kernel command line
+---------------------------------------------
+
+The kernel command line allows to control the TAA mitigations at boot time with
+the option "tsx_async_abort=". The valid arguments for this option are:
+
+  ============  =============================================================
+  off		This option disables the TAA mitigation on affected platforms.
+                If the system has TSX enabled (see next parameter) and the CPU
+                is affected, the system is vulnerable.
+
+  full	        TAA mitigation is enabled. If TSX is enabled, on an affected
+                system it will clear CPU buffers on ring transitions. On
+                systems which are MDS-affected and deploy MDS mitigation,
+                TAA is also mitigated. Specifying this option on those
+                systems will have no effect.
+
+  full,nosmt    The same as tsx_async_abort=full, with SMT disabled on
+                vulnerable CPUs that have TSX enabled. This is the complete
+                mitigation. When TSX is disabled, SMT is not disabled because
+                CPU is not vulnerable to cross-thread TAA attacks.
+  ============  =============================================================
+
+Not specifying this option is equivalent to "tsx_async_abort=full".
+
+The kernel command line also allows to control the TSX feature using the
+parameter "tsx=" on CPUs which support TSX control. MSR_IA32_TSX_CTRL is used
+to control the TSX feature and the enumeration of the TSX feature bits (RTM
+and HLE) in CPUID.
+
+The valid options are:
+
+  ============  =============================================================
+  off		Disables TSX on the system.
+
+                Note that this option takes effect only on newer CPUs which are
+                not vulnerable to MDS, i.e., have MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1
+                and which get the new IA32_TSX_CTRL MSR through a microcode
+                update. This new MSR allows for the reliable deactivation of
+                the TSX functionality.
+
+  on		Enables TSX.
+
+                Although there are mitigations for all known security
+                vulnerabilities, TSX has been known to be an accelerator for
+                several previous speculation-related CVEs, and so there may be
+                unknown security risks associated with leaving it enabled.
+
+  auto		Disables TSX if X86_BUG_TAA is present, otherwise enables TSX
+                on the system.
+  ============  =============================================================
+
+Not specifying this option is equivalent to "tsx=off".
+
+The following combinations of the "tsx_async_abort" and "tsx" are possible. For
+affected platforms tsx=auto is equivalent to tsx=off and the result will be:
+
+  =========  ====================   =========================================
+  tsx=on     tsx_async_abort=full   The system will use VERW to clear CPU
+                                    buffers. Cross-thread attacks still possible
+                                    on SMT machines.
+  tsx=on     tsx_async_abort=full,nosmt As above, cross-thread attacks on SMT
+                                    mitigated.
+  tsx=on     tsx_async_abort=off    The system is vulnerable.
+  tsx=off    tsx_async_abort=full   TSX might be disabled if microcode provides
+                                    a TSX control MSR. If so, system is not
+                                    vulnerable.
+  tsx=off    tsx_async_abort=full,nosmt ditto
+  tsx=off    tsx_async_abort=off    ditto
+  =========  ====================   =========================================
+
+
+For unaffected platforms "tsx=on" and "tsx_async_abort=full" does not clear CPU
+buffers.  For platforms without TSX control (MSR_IA32_ARCH_CAPABILITIES.MDS_NO=0)
+"tsx" command line argument has no effect.
+
+For the affected platforms below table indicates the mitigation status for the
+combinations of CPUID bit MD_CLEAR and IA32_ARCH_CAPABILITIES MSR bits MDS_NO
+and TSX_CTRL_MSR.
+
+  =======  =========  =============  ========================================
+  MDS_NO   MD_CLEAR   TSX_CTRL_MSR   Status
+  =======  =========  =============  ========================================
+    0          0            0        Vulnerable (needs ucode)
+    0          1            0        MDS and TAA mitigated via VERW
+    1          1            0        MDS fixed, TAA vulnerable if TSX enabled
+                                     because MD_CLEAR has no meaning and
+                                     VERW is not guaranteed to clear buffers
+    1          X            1        MDS fixed, TAA can be mitigated by
+                                     VERW or TSX_CTRL_MSR
+  =======  =========  =============  ========================================
+
+Mitigation selection guide
+--------------------------
+
+1. Trusted userspace and guests
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If all user space applications are from a trusted source and do not execute
+untrusted code which is supplied externally, then the mitigation can be
+disabled. The same applies to virtualized environments with trusted guests.
+
+
+2. Untrusted userspace and guests
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If there are untrusted applications or guests on the system, enabling TSX
+might allow a malicious actor to leak data from the host or from other
+processes running on the same physical core.
+
+If the microcode is available and the TSX is disabled on the host, attacks
+are prevented in a virtualized environment as well, even if the VMs do not
+explicitly enable the mitigation.
+
+
+.. _taa_default_mitigations:
+
+Default mitigations
+-------------------
+
+The kernel's default action for vulnerable processors is:
+
+  - Deploy TSX disable mitigation (tsx_async_abort=full tsx=off).
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6e548cddb6c3..fa8f03ddff24 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2636,6 +2636,7 @@
 					       ssbd=force-off [ARM64]
 					       l1tf=off [X86]
 					       mds=off [X86]
+					       tsx_async_abort=off [X86]
 
 			auto (default)
 				Mitigate all CPU vulnerabilities, but leave SMT
@@ -2651,6 +2652,7 @@
 				be fully mitigated, even if it means losing SMT.
 				Equivalent to: l1tf=flush,nosmt [X86]
 					       mds=full,nosmt [X86]
+					       tsx_async_abort=full,nosmt [X86]
 
 	mminit_loglevel=
 			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
@@ -4877,6 +4879,42 @@
 			See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
 			for more details.
 
+	tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
+			Abort (TAA) vulnerability.
+
+			Similar to Micro-architectural Data Sampling (MDS)
+			certain CPUs that support Transactional
+			Synchronization Extensions (TSX) are vulnerable to an
+			exploit against CPU internal buffers which can forward
+			information to a disclosure gadget under certain
+			conditions.
+
+			In vulnerable processors, the speculatively forwarded
+			data can be used in a cache side channel attack, to
+			access data to which the attacker does not have direct
+			access.
+
+			This parameter controls the TAA mitigation.  The
+			options are:
+
+			full       - Enable TAA mitigation on vulnerable CPUs
+				     if TSX is enabled.
+
+			full,nosmt - Enable TAA mitigation and disable SMT on
+				     vulnerable CPUs. If TSX is disabled, SMT
+				     is not disabled because CPU is not
+				     vulnerable to cross-thread TAA attacks.
+			off        - Unconditionally disable TAA mitigation
+
+			Not specifying this option is equivalent to
+			tsx_async_abort=full.  On CPUs which are MDS affected
+			and deploy MDS mitigation, TAA mitigation is not
+			required and doesn't provide any additional
+			mitigation.
+
+			For details see:
+			Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
+
 	turbografx.map[2|3]=	[HW,JOY]
 			TurboGraFX parallel port interface
 			Format:
diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index af64c4bb4447..a8de2fbc1caa 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -27,6 +27,7 @@ x86-specific Documentation
    mds
    microcode
    resctrl_ui
+   tsx_async_abort
    usb-legacy-support
    i386/index
    x86_64/index
diff --git a/Documentation/x86/tsx_async_abort.rst b/Documentation/x86/tsx_async_abort.rst
new file mode 100644
index 000000000000..583ddc185ba2
--- /dev/null
+++ b/Documentation/x86/tsx_async_abort.rst
@@ -0,0 +1,117 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+TSX Async Abort (TAA) mitigation
+================================
+
+.. _tsx_async_abort:
+
+Overview
+--------
+
+TSX Async Abort (TAA) is a side channel attack on internal buffers in some
+Intel processors similar to Microachitectural Data Sampling (MDS).  In this
+case certain loads may speculatively pass invalid data to dependent operations
+when an asynchronous abort condition is pending in a Transactional
+Synchronization Extensions (TSX) transaction.  This includes loads with no
+fault or assist condition. Such loads may speculatively expose stale data from
+the same uarch data structures as in MDS, with same scope of exposure i.e.
+same-thread and cross-thread. This issue affects all current processors that
+support TSX.
+
+Mitigation strategy
+-------------------
+
+a) TSX disable - one of the mitigations is to disable TSX. A new MSR
+IA32_TSX_CTRL will be available in future and current processors after
+microcode update which can be used to disable TSX. In addition, it
+controls the enumeration of the TSX feature bits (RTM and HLE) in CPUID.
+
+b) Clear CPU buffers - similar to MDS, clearing the CPU buffers mitigates this
+vulnerability. More details on this approach can be found in
+:ref:`Documentation/admin-guide/hw-vuln/mds.rst <mds>`.
+
+Kernel internal mitigation modes
+--------------------------------
+
+ =============    ============================================================
+ off              Mitigation is disabled. Either the CPU is not affected or
+                  tsx_async_abort=off is supplied on the kernel command line.
+
+ tsx disabled     Mitigation is enabled. TSX feature is disabled by default at
+                  bootup on processors that support TSX control.
+
+ verw             Mitigation is enabled. CPU is affected and MD_CLEAR is
+                  advertised in CPUID.
+
+ ucode needed     Mitigation is enabled. CPU is affected and MD_CLEAR is not
+                  advertised in CPUID. That is mainly for virtualization
+                  scenarios where the host has the updated microcode but the
+                  hypervisor does not expose MD_CLEAR in CPUID. It's a best
+                  effort approach without guarantee.
+ =============    ============================================================
+
+If the CPU is affected and the "tsx_async_abort" kernel command line parameter is
+not provided then the kernel selects an appropriate mitigation depending on the
+status of RTM and MD_CLEAR CPUID bits.
+
+Below tables indicate the impact of tsx=on|off|auto cmdline options on state of
+TAA mitigation, VERW behavior and TSX feature for various combinations of
+MSR_IA32_ARCH_CAPABILITIES bits.
+
+1. "tsx=off"
+
+=========  =========  ============  ============  ==============  ===================  ======================
+MSR_IA32_ARCH_CAPABILITIES bits     Result with cmdline tsx=off
+----------------------------------  -------------------------------------------------------------------------
+TAA_NO     MDS_NO     TSX_CTRL_MSR  TSX state     VERW can clear  TAA mitigation       TAA mitigation
+                                    after bootup  CPU buffers     tsx_async_abort=off  tsx_async_abort=full
+=========  =========  ============  ============  ==============  ===================  ======================
+    0          0           0         HW default         Yes           Same as MDS           Same as MDS
+    0          0           1        Invalid case   Invalid case       Invalid case          Invalid case
+    0          1           0         HW default         No         Need ucode update     Need ucode update
+    0          1           1          Disabled          Yes           TSX disabled          TSX disabled
+    1          X           1          Disabled           X             None needed           None needed
+=========  =========  ============  ============  ==============  ===================  ======================
+
+2. "tsx=on"
+
+=========  =========  ============  ============  ==============  ===================  ======================
+MSR_IA32_ARCH_CAPABILITIES bits     Result with cmdline tsx=on
+----------------------------------  -------------------------------------------------------------------------
+TAA_NO     MDS_NO     TSX_CTRL_MSR  TSX state     VERW can clear  TAA mitigation       TAA mitigation
+                                    after bootup  CPU buffers     tsx_async_abort=off  tsx_async_abort=full
+=========  =========  ============  ============  ==============  ===================  ======================
+    0          0           0         HW default        Yes            Same as MDS          Same as MDS
+    0          0           1        Invalid case   Invalid case       Invalid case         Invalid case
+    0          1           0         HW default        No          Need ucode update     Need ucode update
+    0          1           1          Enabled          Yes               None              Same as MDS
+    1          X           1          Enabled          X              None needed          None needed
+=========  =========  ============  ============  ==============  ===================  ======================
+
+3. "tsx=auto"
+
+=========  =========  ============  ============  ==============  ===================  ======================
+MSR_IA32_ARCH_CAPABILITIES bits     Result with cmdline tsx=auto
+----------------------------------  -------------------------------------------------------------------------
+TAA_NO     MDS_NO     TSX_CTRL_MSR  TSX state     VERW can clear  TAA mitigation       TAA mitigation
+                                    after bootup  CPU buffers     tsx_async_abort=off  tsx_async_abort=full
+=========  =========  ============  ============  ==============  ===================  ======================
+    0          0           0         HW default    Yes                Same as MDS           Same as MDS
+    0          0           1        Invalid case  Invalid case        Invalid case          Invalid case
+    0          1           0         HW default    No              Need ucode update     Need ucode update
+    0          1           1          Disabled      Yes               TSX disabled          TSX disabled
+    1          X           1          Enabled       X                 None needed           None needed
+=========  =========  ============  ============  ==============  ===================  ======================
+
+In the tables, TSX_CTRL_MSR is a new bit in MSR_IA32_ARCH_CAPABILITIES that
+indicates whether MSR_IA32_TSX_CTRL is supported.
+
+There are two control bits in IA32_TSX_CTRL MSR:
+
+      Bit 0: When set it disables the Restricted Transactional Memory (RTM)
+             sub-feature of TSX (will force all transactions to abort on the
+             XBEGIN instruction).
+
+      Bit 1: When set it disables the enumeration of the RTM and HLE feature
+             (i.e. it will make CPUID(EAX=7).EBX{bit4} and
+             CPUID(EAX=7).EBX{bit11} read as 0).
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 9/9] TAA v2 9
  2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
                   ` (7 preceding siblings ...)
  2019-10-23 10:32 ` [MODERATED] [PATCH 8/9] TAA v2 8 Pawan Gupta
@ 2019-10-23 10:35 ` Michal Hocko
  8 siblings, 0 replies; 11+ messages in thread
From: Michal Hocko @ 2019-10-23 10:35 UTC (permalink / raw)
  To: speck

From: Michal Hocko <mhocko@suse.com>
Subject: [PATCH 9/9] x86/tsx: Add config options to set tsx=on|off|auto

There is a general consensus that TSX usage is not largely spread while
the history shows there is a non trivial space for side channel attacks
possible. Therefore the tsx is disabled by default even on platforms
that might have a safe implementation of TSX according to the current
knowledge. This is a fair trade off to make.

There are, however, workloads that really do benefit from using TSX and
updating to a newer kernel with TSX disabled might introduce a
noticeable regressions. This would be especially a problem for Linux
distributions which will provide TAA mitigations.

Introduce config options X86_INTEL_TSX_MODE_OFF, X86_INTEL_TSX_MODE_ON
and X86_INTEL_TSX_MODE_AUTO to control the TSX feature. The config
setting can be overridden by the tsx cmdline options.

 [ bp: Text cleanups from Josh. ]

Suggested-by: Borislav Petkov <bpetkov@suse.de>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/Kconfig          | 45 +++++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/tsx.c | 22 +++++++++++++------
 2 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index d6e1faa28c58..8ef85139553f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1940,6 +1940,51 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS
 
 	  If unsure, say y.
 
+choice
+	prompt "TSX enable mode"
+	depends on CPU_SUP_INTEL
+	default X86_INTEL_TSX_MODE_OFF
+	help
+	  Intel's TSX (Transactional Synchronization Extensions) feature
+	  allows to optimize locking protocols through lock elision which
+	  can lead to a noticeable performance boost.
+
+	  On the other hand it has been shown that TSX can be exploited
+	  to form side channel attacks (e.g. TAA) and chances are there
+	  will be more of those attacks discovered in the future.
+
+	  Therefore TSX is not enabled by default (aka tsx=off). An admin
+	  might override this decision by tsx=on the command line parameter.
+	  Even with TSX enabled, the kernel will attempt to enable the best
+	  possible TAA mitigation setting depending on the microcode available
+	  for the particular machine.
+
+	  This option allows to set the default tsx mode between tsx=on, =off
+	  and =auto. See Documentation/admin-guide/kernel-parameters.txt for more
+	  details.
+
+	  Say off if not sure, auto if TSX is in use but it should be used on safe
+	  platforms or on if TSX is in use and the security aspect of tsx is not
+	  relevant.
+
+config X86_INTEL_TSX_MODE_OFF
+	bool "off"
+	help
+	  TSX is disabled if possible - equals to tsx=off command line parameter.
+
+config X86_INTEL_TSX_MODE_ON
+	bool "on"
+	help
+	  TSX is always enabled on TSX capable HW - equals the tsx=on command
+	  line parameter.
+
+config X86_INTEL_TSX_MODE_AUTO
+	bool "auto"
+	help
+	  TSX is enabled on TSX capable HW that is believed to be safe against
+	  side channel attacks- equals the tsx=auto command line parameter.
+endchoice
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index dda328ec2ba1..3e20d322bc98 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -73,6 +73,14 @@ static bool __init tsx_ctrl_is_supported(void)
 	return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
 }
 
+static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
+{
+	if (boot_cpu_has_bug(X86_BUG_TAA))
+		return TSX_CTRL_DISABLE;
+
+	return TSX_CTRL_ENABLE;
+}
+
 void __init tsx_init(void)
 {
 	char arg[5] = {};
@@ -88,17 +96,19 @@ void __init tsx_init(void)
 		} else if (!strcmp(arg, "off")) {
 			tsx_ctrl_state = TSX_CTRL_DISABLE;
 		} else if (!strcmp(arg, "auto")) {
-			if (boot_cpu_has_bug(X86_BUG_TAA))
-				tsx_ctrl_state = TSX_CTRL_DISABLE;
-			else
-				tsx_ctrl_state = TSX_CTRL_ENABLE;
+			tsx_ctrl_state = x86_get_tsx_auto_mode();
 		} else {
 			tsx_ctrl_state = TSX_CTRL_DISABLE;
 			pr_err("tsx: invalid option, defaulting to off\n");
 		}
 	} else {
-		/* tsx= not provided, defaulting to off */
-		tsx_ctrl_state = TSX_CTRL_DISABLE;
+		/* tsx= not provided */
+		if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
+			tsx_ctrl_state = x86_get_tsx_auto_mode();
+		else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
+			tsx_ctrl_state = TSX_CTRL_DISABLE;
+		else
+			tsx_ctrl_state = TSX_CTRL_ENABLE;
 	}
 
 	if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* [MODERATED] [PATCH 0/9] TAA v2 0
@ 2019-10-27  9:35 Borislav Petkov
  2019-10-23  8:45 ` [MODERATED] [PATCH 1/9] TAA v2 1 Pawan Gupta
                   ` (8 more replies)
  0 siblings, 9 replies; 11+ messages in thread
From: Borislav Petkov @ 2019-10-27  9:35 UTC (permalink / raw)
  To: speck

From: Borislav Petkov <bp@suse.de>
Subject: [PATCH 0/9] TAA v2

Hi,

lemme send the pile out one more time before I leave for OSS EU in Lyon.
Patch 6 is still there until Paolo and Tony have figured out what should
happen with guests.

changelog:
==========

v1:

here's the pile I've picked up. I've incorporated as much of the
feedback as possible, scream loudly if something's missing. First
testing looks good.

We'll cast them in stone in the coming days because distros and stable
have to start backporting soon. All fixes will go ontop, as in previous
occasions.

Michal Hocko (1):
  x86/tsx: Add config options to set tsx=on|off|auto

Pawan Gupta (8):
  x86/msr: Add the IA32_TSX_CTRL MSR
  x86/cpu: Add a helper function x86_read_arch_cap_msr()
  x86/cpu: Add a "tsx=" cmdline option with TSX disabled by default
  x86/speculation/taa: Add mitigation for TSX Async Abort
  x86/speculation/taa: Add sysfs reporting for TSX Async Abort
  kvm/x86: Export MDS_NO=0 to guests when TSX is enabled
  x86/tsx: Add "auto" option to the tsx= cmdline parameter
  x86/speculation/taa: Add documentation for TSX Async Abort

 .../ABI/testing/sysfs-devices-system-cpu      |   1 +
 Documentation/admin-guide/hw-vuln/index.rst   |   1 +
 .../admin-guide/hw-vuln/tsx_async_abort.rst   | 276 ++++++++++++++++++
 .../admin-guide/kernel-parameters.txt         |  67 +++++
 Documentation/x86/index.rst                   |   1 +
 Documentation/x86/tsx_async_abort.rst         | 117 ++++++++
 arch/x86/Kconfig                              |  45 +++
 arch/x86/include/asm/cpufeatures.h            |   1 +
 arch/x86/include/asm/msr-index.h              |   9 +
 arch/x86/include/asm/nospec-branch.h          |   4 +-
 arch/x86/include/asm/processor.h              |   7 +
 arch/x86/kernel/cpu/Makefile                  |   2 +-
 arch/x86/kernel/cpu/bugs.c                    | 131 +++++++++
 arch/x86/kernel/cpu/common.c                  |  32 +-
 arch/x86/kernel/cpu/cpu.h                     |  18 ++
 arch/x86/kernel/cpu/intel.c                   |   5 +
 arch/x86/kernel/cpu/tsx.c                     | 140 +++++++++
 arch/x86/kvm/x86.c                            |  19 ++
 drivers/base/cpu.c                            |   9 +
 include/linux/cpu.h                           |   3 +
 20 files changed, 881 insertions(+), 7 deletions(-)
 create mode 100644 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
 create mode 100644 Documentation/x86/tsx_async_abort.rst
 create mode 100644 arch/x86/kernel/cpu/tsx.c

-- 
2.21.0

^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH 2/9] TAA v2 2
  2019-10-23  8:52 ` [MODERATED] [PATCH 2/9] TAA v2 2 Pawan Gupta
@ 2019-10-28  7:36   ` Thomas Gleixner
  0 siblings, 0 replies; 11+ messages in thread
From: Thomas Gleixner @ 2019-10-28  7:36 UTC (permalink / raw)
  To: speck

On Wed, 23 Oct 2019, speck for Pawan Gupta wrote:
> ---
>  arch/x86/kernel/cpu/common.c | 15 +++++++++++----


> -static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
> +u64 x86_read_arch_cap_msr(void)

Where is the declaration of this? In the next patch ....

Oh well.

^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2019-10-28  7:36 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-27  9:35 [MODERATED] [PATCH 0/9] TAA v2 0 Borislav Petkov
2019-10-23  8:45 ` [MODERATED] [PATCH 1/9] TAA v2 1 Pawan Gupta
2019-10-23  8:52 ` [MODERATED] [PATCH 2/9] TAA v2 2 Pawan Gupta
2019-10-28  7:36   ` Thomas Gleixner
2019-10-23  9:01 ` [MODERATED] [PATCH 3/9] TAA v2 3 Pawan Gupta
2019-10-23  9:30 ` [MODERATED] [PATCH 4/9] TAA v2 4 Pawan Gupta
2019-10-23 10:19 ` [MODERATED] [PATCH 5/9] TAA v2 5 Pawan Gupta
2019-10-23 10:23 ` [MODERATED] [PATCH 6/9] TAA v2 6 Pawan Gupta
2019-10-23 10:28 ` [MODERATED] [PATCH 7/9] TAA v2 7 Pawan Gupta
2019-10-23 10:32 ` [MODERATED] [PATCH 8/9] TAA v2 8 Pawan Gupta
2019-10-23 10:35 ` [MODERATED] [PATCH 9/9] TAA v2 9 Michal Hocko

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