x86/bugs: Add a Transient Scheduler Attacks mitigation

Commit d8010d4 upstream.

Add the required features detection glue to bugs.c et all in order to
support the TSA mitigation.

Co-developed-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: bp3tk0v

Documentation/ABI/testing/sysfs-devices-system-cpu

@@ -526,6 +526,7 @@ What:		/sys/devices/system/cpu/vulnerabilities
 		/sys/devices/system/cpu/vulnerabilities/spectre_v1
 		/sys/devices/system/cpu/vulnerabilities/spectre_v2
 		/sys/devices/system/cpu/vulnerabilities/srbds
+		/sys/devices/system/cpu/vulnerabilities/tsa
 		/sys/devices/system/cpu/vulnerabilities/tsx_async_abort
 Date:		January 2018
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -6645,6 +6645,19 @@
 			If not specified, "default" is used. In this case,
 			the RNG's choice is left to each individual trust source.
 
+	tsa=		[X86] Control mitigation for Transient Scheduler
+			Attacks on AMD CPUs. Search the following in your
+			favourite search engine for more details:
+
+			"Technical guidance for mitigating transient scheduler
+			attacks".
+
+			off		- disable the mitigation
+			on		- enable the mitigation (default)
+			user		- mitigate only user/kernel transitions
+			vm		- mitigate only guest/host transitions
+
+
 	tsc=		Disable clocksource stability checks for TSC.
 			Format: <string>
 			[x86] reliable: mark tsc clocksource as reliable, this

arch/x86/Kconfig

@@ -2621,6 +2621,15 @@ config MITIGATION_ITS
 	  disabled, mitigation cannot be enabled via cmdline.
 	  See <file:Documentation/admin-guide/hw-vuln/indirect-target-selection.rst>
 
+config MITIGATION_TSA
+	bool "Mitigate Transient Scheduler Attacks"
+	depends on CPU_SUP_AMD
+	default y
+	help
+	  Enable mitigation for Transient Scheduler Attacks. TSA is a hardware
+	  security vulnerability on AMD CPUs which can lead to forwarding of
+	  invalid info to subsequent instructions and thus can affect their
+	  timing and thereby cause a leakage.
 endif
 
 config ARCH_HAS_ADD_PAGES

arch/x86/include/asm/cpu.h

@@ -81,4 +81,16 @@ int intel_microcode_sanity_check(void *mc, bool print_err, int hdr_type);
 
 extern struct cpumask cpus_stop_mask;
 
+union zen_patch_rev {
+	struct {
+		__u32 rev	 : 8,
+		      stepping	 : 4,
+		      model	 : 4,
+		      __reserved : 4,
+		      ext_model	 : 4,
+		      ext_fam	 : 8;
+	};
+	__u32 ucode_rev;
+};
+
 #endif /* _ASM_X86_CPU_H */

arch/x86/include/asm/cpufeatures.h

@@ -449,6 +449,7 @@
 /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */
 #define X86_FEATURE_NO_NESTED_DATA_BP	(20*32+ 0) /* "" No Nested Data Breakpoints */
 #define X86_FEATURE_LFENCE_RDTSC	(20*32+ 2) /* "" LFENCE always serializing / synchronizes RDTSC */
+#define X86_FEATURE_VERW_CLEAR		(20*32+ 5) /* "" The memory form of VERW mitigates TSA */
 #define X86_FEATURE_NULL_SEL_CLR_BASE	(20*32+ 6) /* "" Null Selector Clears Base */
 #define X86_FEATURE_AUTOIBRS		(20*32+ 8) /* "" Automatic IBRS */
 #define X86_FEATURE_NO_SMM_CTL_MSR	(20*32+ 9) /* "" SMM_CTL MSR is not present */
@@ -470,6 +471,10 @@
 #define X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT (21*32+ 4) /* "" Clear branch history at vmexit using SW loop */
 #define X86_FEATURE_INDIRECT_THUNK_ITS	(21*32 + 5) /* "" Use thunk for indirect branches in lower half of cacheline */
 
+#define X86_FEATURE_TSA_SQ_NO          (21*32+11) /* "" AMD CPU not vulnerable to TSA-SQ */
+#define X86_FEATURE_TSA_L1_NO          (21*32+12) /* "" AMD CPU not vulnerable to TSA-L1 */
+#define X86_FEATURE_CLEAR_CPU_BUF_VM   (21*32+13) /* "" Clear CPU buffers using VERW before VMRUN */
+
 /*
  * BUG word(s)
  */
@@ -521,4 +526,5 @@
 #define X86_BUG_IBPB_NO_RET		X86_BUG(1*32 + 4) /* "ibpb_no_ret" IBPB omits return target predictions */
 #define X86_BUG_ITS			X86_BUG(1*32 + 5) /* CPU is affected by Indirect Target Selection */
 #define X86_BUG_ITS_NATIVE_ONLY		X86_BUG(1*32 + 6) /* CPU is affected by ITS, VMX is not affected */
+#define X86_BUG_TSA			X86_BUG(1*32+ 9) /* "tsa" CPU is affected by Transient Scheduler Attacks */
 #endif /* _ASM_X86_CPUFEATURES_H */

arch/x86/include/asm/mwait.h

@@ -80,7 +80,7 @@ static __always_inline void __mwait(unsigned long eax, unsigned long ecx)
 static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx,
 				     unsigned long ecx)
 {
-	/* No MDS buffer clear as this is AMD/HYGON only */
+	/* No need for TSA buffer clearing on AMD */
 
 	/* "mwaitx %eax, %ebx, %ecx;" */
 	asm volatile(".byte 0x0f, 0x01, 0xfb;"

arch/x86/include/asm/nospec-branch.h

@@ -330,19 +330,25 @@
  * CFLAGS.ZF.
  * Note: Only the memory operand variant of VERW clears the CPU buffers.
  */
-.macro CLEAR_CPU_BUFFERS
+.macro __CLEAR_CPU_BUFFERS feature
 #ifdef CONFIG_X86_64
-	ALTERNATIVE "", "verw x86_verw_sel(%rip)", X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE "", "verw x86_verw_sel(%rip)", \feature
 #else
 	/*
 	 * In 32bit mode, the memory operand must be a %cs reference. The data
 	 * segments may not be usable (vm86 mode), and the stack segment may not
 	 * be flat (ESPFIX32).
 	 */
-	ALTERNATIVE "", "verw %cs:x86_verw_sel", X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE "", "verw %cs:x86_verw_sel", \feature
 #endif
 .endm
 
+#define CLEAR_CPU_BUFFERS \
+	__CLEAR_CPU_BUFFERS X86_FEATURE_CLEAR_CPU_BUF
+
+#define VM_CLEAR_CPU_BUFFERS \
+	__CLEAR_CPU_BUFFERS X86_FEATURE_CLEAR_CPU_BUF_VM
+
 #ifdef CONFIG_X86_64
 .macro CLEAR_BRANCH_HISTORY
 	ALTERNATIVE "", "call clear_bhb_loop", X86_FEATURE_CLEAR_BHB_LOOP
@@ -627,7 +633,7 @@ static __always_inline void x86_clear_cpu_buffers(void)
 
 /**
  * x86_idle_clear_cpu_buffers - Buffer clearing support in idle for the MDS
- * vulnerability
+ * and TSA vulnerabilities.
  *
  * Clear CPU buffers if the corresponding static key is enabled
  */

arch/x86/kernel/cpu/amd.c

@@ -539,6 +539,63 @@ static void early_init_amd_mc(struct cpuinfo_x86 *c)
 #endif
 }
 
+static bool amd_check_tsa_microcode(void)
+{
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+	union zen_patch_rev p;
+	u32 min_rev = 0;
+
+	p.ext_fam	= c->x86 - 0xf;
+	p.model		= c->x86_model;
+	p.stepping	= c->x86_stepping;
+
+	if (cpu_has(c, X86_FEATURE_ZEN3) ||
+	    cpu_has(c, X86_FEATURE_ZEN4)) {
+		switch (p.ucode_rev >> 8) {
+		case 0xa0011:	min_rev = 0x0a0011d7; break;
+		case 0xa0012:	min_rev = 0x0a00123b; break;
+		case 0xa0082:	min_rev = 0x0a00820d; break;
+		case 0xa1011:	min_rev = 0x0a10114c; break;
+		case 0xa1012:	min_rev = 0x0a10124c; break;
+		case 0xa1081:	min_rev = 0x0a108109; break;
+		case 0xa2010:	min_rev = 0x0a20102e; break;
+		case 0xa2012:	min_rev = 0x0a201211; break;
+		case 0xa4041:	min_rev = 0x0a404108; break;
+		case 0xa5000:	min_rev = 0x0a500012; break;
+		case 0xa6012:	min_rev = 0x0a60120a; break;
+		case 0xa7041:	min_rev = 0x0a704108; break;
+		case 0xa7052:	min_rev = 0x0a705208; break;
+		case 0xa7080:	min_rev = 0x0a708008; break;
+		case 0xa70c0:	min_rev = 0x0a70c008; break;
+		case 0xaa002:	min_rev = 0x0aa00216; break;
+		default:
+			pr_debug("%s: ucode_rev: 0x%x, current revision: 0x%x\n",
+				 __func__, p.ucode_rev, c->microcode);
+			return false;
+		}
+	}
+
+	if (!min_rev)
+		return false;
+
+	return c->microcode >= min_rev;
+}
+
+static void tsa_init(struct cpuinfo_x86 *c)
+{
+	if (cpu_has(c, X86_FEATURE_HYPERVISOR))
+		return;
+
+	if (cpu_has(c, X86_FEATURE_ZEN3) ||
+	    cpu_has(c, X86_FEATURE_ZEN4)) {
+		if (amd_check_tsa_microcode())
+			setup_force_cpu_cap(X86_FEATURE_VERW_CLEAR);
+	} else {
+		setup_force_cpu_cap(X86_FEATURE_TSA_SQ_NO);
+		setup_force_cpu_cap(X86_FEATURE_TSA_L1_NO);
+	}
+}
+
 static void bsp_init_amd(struct cpuinfo_x86 *c)
 {
 	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
@@ -645,6 +702,9 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
 		break;
 	}
 
+
+	tsa_init(c);
+
 	return;
 
 warn:

arch/x86/kernel/cpu/bugs.c

@@ -50,6 +50,7 @@ static void __init l1d_flush_select_mitigation(void);
 static void __init srso_select_mitigation(void);
 static void __init gds_select_mitigation(void);
 static void __init its_select_mitigation(void);
+static void __init tsa_select_mitigation(void);
 
 /* The base value of the SPEC_CTRL MSR without task-specific bits set */
 u64 x86_spec_ctrl_base;
@@ -185,6 +186,7 @@ void __init cpu_select_mitigations(void)
 	srso_select_mitigation();
 	gds_select_mitigation();
 	its_select_mitigation();
+	tsa_select_mitigation();
 }
 
 /*
@@ -2093,6 +2095,94 @@ static void update_mds_branch_idle(void)
 #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"
 #define MMIO_MSG_SMT "MMIO Stale Data CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html for more details.\n"
 
+#undef pr_fmt
+#define pr_fmt(fmt)	"Transient Scheduler Attacks: " fmt
+
+enum tsa_mitigations {
+	TSA_MITIGATION_NONE,
+	TSA_MITIGATION_UCODE_NEEDED,
+	TSA_MITIGATION_USER_KERNEL,
+	TSA_MITIGATION_VM,
+	TSA_MITIGATION_FULL,
+};
+
+static const char * const tsa_strings[] = {
+	[TSA_MITIGATION_NONE]		= "Vulnerable",
+	[TSA_MITIGATION_UCODE_NEEDED]	= "Vulnerable: Clear CPU buffers attempted, no microcode",
+	[TSA_MITIGATION_USER_KERNEL]	= "Mitigation: Clear CPU buffers: user/kernel boundary",
+	[TSA_MITIGATION_VM]		= "Mitigation: Clear CPU buffers: VM",
+	[TSA_MITIGATION_FULL]		= "Mitigation: Clear CPU buffers",
+};
+
+static enum tsa_mitigations tsa_mitigation __ro_after_init =
+	IS_ENABLED(CONFIG_MITIGATION_TSA) ? TSA_MITIGATION_FULL : TSA_MITIGATION_NONE;
+
+static int __init tsa_parse_cmdline(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "off"))
+		tsa_mitigation = TSA_MITIGATION_NONE;
+	else if (!strcmp(str, "on"))
+		tsa_mitigation = TSA_MITIGATION_FULL;
+	else if (!strcmp(str, "user"))
+		tsa_mitigation = TSA_MITIGATION_USER_KERNEL;
+	else if (!strcmp(str, "vm"))
+		tsa_mitigation = TSA_MITIGATION_VM;
+	else
+		pr_err("Ignoring unknown tsa=%s option.\n", str);
+
+	return 0;
+}
+early_param("tsa", tsa_parse_cmdline);
+
+static void __init tsa_select_mitigation(void)
+{
+	if (tsa_mitigation == TSA_MITIGATION_NONE)
+		return;
+
+	if (cpu_mitigations_off() || !boot_cpu_has_bug(X86_BUG_TSA)) {
+		tsa_mitigation = TSA_MITIGATION_NONE;
+		return;
+	}
+
+	if (!boot_cpu_has(X86_FEATURE_VERW_CLEAR))
+		tsa_mitigation = TSA_MITIGATION_UCODE_NEEDED;
+
+	switch (tsa_mitigation) {
+	case TSA_MITIGATION_USER_KERNEL:
+		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+		break;
+
+	case TSA_MITIGATION_VM:
+		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF_VM);
+		break;
+
+	case TSA_MITIGATION_UCODE_NEEDED:
+		if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
+			goto out;
+
+		pr_notice("Forcing mitigation on in a VM\n");
+
+		/*
+		 * On the off-chance that microcode has been updated
+		 * on the host, enable the mitigation in the guest just
+		 * in case.
+		 */
+		fallthrough;
+	case TSA_MITIGATION_FULL:
+		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF_VM);
+		break;
+	default:
+		break;
+	}
+
+out:
+	pr_info("%s\n", tsa_strings[tsa_mitigation]);
+}
+
 void cpu_bugs_smt_update(void)
 {
 	mutex_lock(&spec_ctrl_mutex);
@@ -2146,6 +2236,24 @@ void cpu_bugs_smt_update(void)
 		break;
 	}
 
+	switch (tsa_mitigation) {
+	case TSA_MITIGATION_USER_KERNEL:
+	case TSA_MITIGATION_VM:
+	case TSA_MITIGATION_FULL:
+	case TSA_MITIGATION_UCODE_NEEDED:
+		/*
+		 * TSA-SQ can potentially lead to info leakage between
+		 * SMT threads.
+		 */
+		if (sched_smt_active())
+			static_branch_enable(&cpu_buf_idle_clear);
+		else
+			static_branch_disable(&cpu_buf_idle_clear);
+		break;
+	case TSA_MITIGATION_NONE:
+		break;
+	}
+
 	mutex_unlock(&spec_ctrl_mutex);
 }
 
@@ -3075,6 +3183,11 @@ static ssize_t gds_show_state(char *buf)
 	return sysfs_emit(buf, "%s\n", gds_strings[gds_mitigation]);
 }
 
+static ssize_t tsa_show_state(char *buf)
+{
+	return sysfs_emit(buf, "%s\n", tsa_strings[tsa_mitigation]);
+}
+
 static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
 			       char *buf, unsigned int bug)
 {
@@ -3136,6 +3249,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 	case X86_BUG_ITS:
 		return its_show_state(buf);
 
+	case X86_BUG_TSA:
+		return tsa_show_state(buf);
+
 	default:
 		break;
 	}
@@ -3220,4 +3336,9 @@ ssize_t cpu_show_indirect_target_selection(struct device *dev, struct device_att
 {
 	return cpu_show_common(dev, attr, buf, X86_BUG_ITS);
 }
+
+ssize_t cpu_show_tsa(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return cpu_show_common(dev, attr, buf, X86_BUG_TSA);
+}
 #endif