[PATCH stable 4.9 23/23] powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit

[Michael Ellerman <mpe@ellerman.id.au>]

From: Nicholas Piggin <npiggin@gmail.com>

commit a048a07d7f4535baa4cbad6bc024f175317ab938 upstream.

On some CPUs we can prevent a vulnerability related to store-to-load
forwarding by preventing store forwarding between privilege domains,
by inserting a barrier in kernel entry and exit paths.

This is known to be the case on at least Power7, Power8 and Power9
powerpc CPUs.

Barriers must be inserted generally before the first load after moving
to a higher privilege, and after the last store before moving to a
lower privilege, HV and PR privilege transitions must be protected.

Barriers are added as patch sections, with all kernel/hypervisor entry
points patched, and the exit points to lower privilge levels patched
similarly to the RFI flush patching.

Firmware advertisement is not implemented yet, so CPU flush types
are hard coded.

Thanks to Michal Suchánek for bug fixes and review.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michal Suchánek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/powerpc/include/asm/exception-64s.h     |  29 ++++++
 arch/powerpc/include/asm/feature-fixups.h    |  19 ++++
 arch/powerpc/include/asm/security_features.h |  11 ++
 arch/powerpc/kernel/exceptions-64s.S         |  16 ++-
 arch/powerpc/kernel/security.c               | 149 +++++++++++++++++++++++++++
 arch/powerpc/kernel/vmlinux.lds.S            |  14 +++
 arch/powerpc/lib/feature-fixups.c            | 115 +++++++++++++++++++++
 arch/powerpc/platforms/powernv/setup.c       |   1 +
 arch/powerpc/platforms/pseries/setup.c       |   1 +
 9 files changed, 354 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 903e76a9f158..e2200100828d 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -51,6 +51,27 @@
 #define EX_PPR		88	/* SMT thread status register (priority) */
 #define EX_CTR		96
 
+#define STF_ENTRY_BARRIER_SLOT						\
+	STF_ENTRY_BARRIER_FIXUP_SECTION;				\
+	nop;								\
+	nop;								\
+	nop
+
+#define STF_EXIT_BARRIER_SLOT						\
+	STF_EXIT_BARRIER_FIXUP_SECTION;					\
+	nop;								\
+	nop;								\
+	nop;								\
+	nop;								\
+	nop;								\
+	nop
+
+/*
+ * r10 must be free to use, r13 must be paca
+ */
+#define INTERRUPT_TO_KERNEL						\
+	STF_ENTRY_BARRIER_SLOT
+
 /*
  * Macros for annotating the expected destination of (h)rfid
  *
@@ -67,16 +88,19 @@
 	rfid
 
 #define RFI_TO_USER							\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	rfid;								\
 	b	rfi_flush_fallback
 
 #define RFI_TO_USER_OR_KERNEL						\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	rfid;								\
 	b	rfi_flush_fallback
 
 #define RFI_TO_GUEST							\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	rfid;								\
 	b	rfi_flush_fallback
@@ -85,21 +109,25 @@
 	hrfid
 
 #define HRFI_TO_USER							\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	hrfid;								\
 	b	hrfi_flush_fallback
 
 #define HRFI_TO_USER_OR_KERNEL						\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	hrfid;								\
 	b	hrfi_flush_fallback
 
 #define HRFI_TO_GUEST							\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	hrfid;								\
 	b	hrfi_flush_fallback
 
 #define HRFI_TO_UNKNOWN							\
+	STF_EXIT_BARRIER_SLOT;						\
 	RFI_FLUSH_SLOT;							\
 	hrfid;								\
 	b	hrfi_flush_fallback
@@ -225,6 +253,7 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 #define __EXCEPTION_PROLOG_1(area, extra, vec)				\
 	OPT_SAVE_REG_TO_PACA(area+EX_PPR, r9, CPU_FTR_HAS_PPR);		\
 	OPT_SAVE_REG_TO_PACA(area+EX_CFAR, r10, CPU_FTR_CFAR);		\
+	INTERRUPT_TO_KERNEL;						\
 	SAVE_CTR(r10, area);						\
 	mfcr	r9;							\
 	extra(vec);							\
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 7b332342071c..0bf8202feca6 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -189,6 +189,22 @@ void apply_feature_fixups(void);
 void setup_feature_keys(void);
 #endif
 
+#define STF_ENTRY_BARRIER_FIXUP_SECTION			\
+953:							\
+	.pushsection __stf_entry_barrier_fixup,"a";	\
+	.align 2;					\
+954:							\
+	FTR_ENTRY_OFFSET 953b-954b;			\
+	.popsection;
+
+#define STF_EXIT_BARRIER_FIXUP_SECTION			\
+955:							\
+	.pushsection __stf_exit_barrier_fixup,"a";	\
+	.align 2;					\
+956:							\
+	FTR_ENTRY_OFFSET 955b-956b;			\
+	.popsection;
+
 #define RFI_FLUSH_FIXUP_SECTION				\
 951:							\
 	.pushsection __rfi_flush_fixup,"a";		\
@@ -200,6 +216,9 @@ void setup_feature_keys(void);
 
 #ifndef __ASSEMBLY__
 
+extern long stf_barrier_fallback;
+extern long __start___stf_entry_barrier_fixup, __stop___stf_entry_barrier_fixup;
+extern long __start___stf_exit_barrier_fixup, __stop___stf_exit_barrier_fixup;
 extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup;
 
 #endif
diff --git a/arch/powerpc/include/asm/security_features.h b/arch/powerpc/include/asm/security_features.h
index fa4d2e1cf772..44989b22383c 100644
--- a/arch/powerpc/include/asm/security_features.h
+++ b/arch/powerpc/include/asm/security_features.h
@@ -12,6 +12,17 @@
 extern unsigned long powerpc_security_features;
 extern bool rfi_flush;
 
+/* These are bit flags */
+enum stf_barrier_type {
+	STF_BARRIER_NONE	= 0x1,
+	STF_BARRIER_FALLBACK	= 0x2,
+	STF_BARRIER_EIEIO	= 0x4,
+	STF_BARRIER_SYNC_ORI	= 0x8,
+};
+
+void setup_stf_barrier(void);
+void do_stf_barrier_fixups(enum stf_barrier_type types);
+
 static inline void security_ftr_set(unsigned long feature)
 {
 	powerpc_security_features |= feature;
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 94b5dfb087e9..d50cc9b38b80 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -846,7 +846,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 #endif
 
 
-EXC_REAL_MASKABLE(decrementer, 0x900, 0x980)
+EXC_REAL_OOL_MASKABLE(decrementer, 0x900, 0x980)
 EXC_VIRT_MASKABLE(decrementer, 0x4900, 0x4980, 0x900)
 TRAMP_KVM(PACA_EXGEN, 0x900)
 EXC_COMMON_ASYNC(decrementer_common, 0x900, timer_interrupt)
@@ -884,6 +884,7 @@ BEGIN_FTR_SECTION						\
 END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE)				\
 	mr	r9,r13 ;					\
 	GET_PACA(r13) ;						\
+	INTERRUPT_TO_KERNEL ;					\
 	mfspr	r11,SPRN_SRR0 ;					\
 0:
 
@@ -1353,6 +1354,19 @@ masked_##_H##interrupt:					\
 	##_H##RFI_TO_KERNEL;				\
 	b	.
 
+TRAMP_REAL_BEGIN(stf_barrier_fallback)
+	std	r9,PACA_EXRFI+EX_R9(r13)
+	std	r10,PACA_EXRFI+EX_R10(r13)
+	sync
+	ld	r9,PACA_EXRFI+EX_R9(r13)
+	ld	r10,PACA_EXRFI+EX_R10(r13)
+	ori	31,31,0
+	.rept 14
+	b	1f
+1:
+	.endr
+	blr
+
 /*
  * Real mode exceptions actually use this too, but alternate
  * instruction code patches (which end up in the common .text area)
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index bab5a27ea805..2277df84ef6e 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -5,6 +5,7 @@
 // Copyright 2018, Michael Ellerman, IBM Corporation.
 
 #include <linux/kernel.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/seq_buf.h>
 
@@ -86,3 +87,151 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, c
 
 	return s.len;
 }
+
+/*
+ * Store-forwarding barrier support.
+ */
+
+static enum stf_barrier_type stf_enabled_flush_types;
+static bool no_stf_barrier;
+bool stf_barrier;
+
+static int __init handle_no_stf_barrier(char *p)
+{
+	pr_info("stf-barrier: disabled on command line.");
+	no_stf_barrier = true;
+	return 0;
+}
+
+early_param("no_stf_barrier", handle_no_stf_barrier);
+
+/* This is the generic flag used by other architectures */
+static int __init handle_ssbd(char *p)
+{
+	if (!p || strncmp(p, "auto", 5) == 0 || strncmp(p, "on", 2) == 0 ) {
+		/* Until firmware tells us, we have the barrier with auto */
+		return 0;
+	} else if (strncmp(p, "off", 3) == 0) {
+		handle_no_stf_barrier(NULL);
+		return 0;
+	} else
+		return 1;
+
+	return 0;
+}
+early_param("spec_store_bypass_disable", handle_ssbd);
+
+/* This is the generic flag used by other architectures */
+static int __init handle_no_ssbd(char *p)
+{
+	handle_no_stf_barrier(NULL);
+	return 0;
+}
+early_param("nospec_store_bypass_disable", handle_no_ssbd);
+
+static void stf_barrier_enable(bool enable)
+{
+	if (enable)
+		do_stf_barrier_fixups(stf_enabled_flush_types);
+	else
+		do_stf_barrier_fixups(STF_BARRIER_NONE);
+
+	stf_barrier = enable;
+}
+
+void setup_stf_barrier(void)
+{
+	enum stf_barrier_type type;
+	bool enable, hv;
+
+	hv = cpu_has_feature(CPU_FTR_HVMODE);
+
+	/* Default to fallback in case fw-features are not available */
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		type = STF_BARRIER_EIEIO;
+	else if (cpu_has_feature(CPU_FTR_ARCH_207S))
+		type = STF_BARRIER_SYNC_ORI;
+	else if (cpu_has_feature(CPU_FTR_ARCH_206))
+		type = STF_BARRIER_FALLBACK;
+	else
+		type = STF_BARRIER_NONE;
+
+	enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
+		(security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR) ||
+		 (security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) && hv));
+
+	if (type == STF_BARRIER_FALLBACK) {
+		pr_info("stf-barrier: fallback barrier available\n");
+	} else if (type == STF_BARRIER_SYNC_ORI) {
+		pr_info("stf-barrier: hwsync barrier available\n");
+	} else if (type == STF_BARRIER_EIEIO) {
+		pr_info("stf-barrier: eieio barrier available\n");
+	}
+
+	stf_enabled_flush_types = type;
+
+	if (!no_stf_barrier)
+		stf_barrier_enable(enable);
+}
+
+ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	if (stf_barrier && stf_enabled_flush_types != STF_BARRIER_NONE) {
+		const char *type;
+		switch (stf_enabled_flush_types) {
+		case STF_BARRIER_EIEIO:
+			type = "eieio";
+			break;
+		case STF_BARRIER_SYNC_ORI:
+			type = "hwsync";
+			break;
+		case STF_BARRIER_FALLBACK:
+			type = "fallback";
+			break;
+		default:
+			type = "unknown";
+		}
+		return sprintf(buf, "Mitigation: Kernel entry/exit barrier (%s)\n", type);
+	}
+
+	if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
+	    !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
+		return sprintf(buf, "Not affected\n");
+
+	return sprintf(buf, "Vulnerable\n");
+}
+
+#ifdef CONFIG_DEBUG_FS
+static int stf_barrier_set(void *data, u64 val)
+{
+	bool enable;
+
+	if (val == 1)
+		enable = true;
+	else if (val == 0)
+		enable = false;
+	else
+		return -EINVAL;
+
+	/* Only do anything if we're changing state */
+	if (enable != stf_barrier)
+		stf_barrier_enable(enable);
+
+	return 0;
+}
+
+static int stf_barrier_get(void *data, u64 *val)
+{
+	*val = stf_barrier ? 1 : 0;
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_stf_barrier, stf_barrier_get, stf_barrier_set, "%llu\n");
+
+static __init int stf_barrier_debugfs_init(void)
+{
+	debugfs_create_file("stf_barrier", 0600, powerpc_debugfs_root, NULL, &fops_stf_barrier);
+	return 0;
+}
+device_initcall(stf_barrier_debugfs_init);
+#endif /* CONFIG_DEBUG_FS */
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index b61fb7902018..c16fddbb6ab8 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -133,6 +133,20 @@ SECTIONS
 	RODATA
 
 #ifdef CONFIG_PPC64
+	. = ALIGN(8);
+	__stf_entry_barrier_fixup : AT(ADDR(__stf_entry_barrier_fixup) - LOAD_OFFSET) {
+		__start___stf_entry_barrier_fixup = .;
+		*(__stf_entry_barrier_fixup)
+		__stop___stf_entry_barrier_fixup = .;
+	}
+
+	. = ALIGN(8);
+	__stf_exit_barrier_fixup : AT(ADDR(__stf_exit_barrier_fixup) - LOAD_OFFSET) {
+		__start___stf_exit_barrier_fixup = .;
+		*(__stf_exit_barrier_fixup)
+		__stop___stf_exit_barrier_fixup = .;
+	}
+
 	. = ALIGN(8);
 	__rfi_flush_fixup : AT(ADDR(__rfi_flush_fixup) - LOAD_OFFSET) {
 		__start___rfi_flush_fixup = .;
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index d89d54fa6acc..cf1398e3c2e0 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -22,6 +22,7 @@
 #include <asm/page.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
+#include <asm/security_features.h>
 #include <asm/firmware.h>
 #include <asm/setup.h>
 
@@ -117,6 +118,120 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 }
 
 #ifdef CONFIG_PPC_BOOK3S_64
+void do_stf_entry_barrier_fixups(enum stf_barrier_type types)
+{
+	unsigned int instrs[3], *dest;
+	long *start, *end;
+	int i;
+
+	start = PTRRELOC(&__start___stf_entry_barrier_fixup),
+	end = PTRRELOC(&__stop___stf_entry_barrier_fixup);
+
+	instrs[0] = 0x60000000; /* nop */
+	instrs[1] = 0x60000000; /* nop */
+	instrs[2] = 0x60000000; /* nop */
+
+	i = 0;
+	if (types & STF_BARRIER_FALLBACK) {
+		instrs[i++] = 0x7d4802a6; /* mflr r10		*/
+		instrs[i++] = 0x60000000; /* branch patched below */
+		instrs[i++] = 0x7d4803a6; /* mtlr r10		*/
+	} else if (types & STF_BARRIER_EIEIO) {
+		instrs[i++] = 0x7e0006ac; /* eieio + bit 6 hint */
+	} else if (types & STF_BARRIER_SYNC_ORI) {
+		instrs[i++] = 0x7c0004ac; /* hwsync		*/
+		instrs[i++] = 0xe94d0000; /* ld r10,0(r13)	*/
+		instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */
+	}
+
+	for (i = 0; start < end; start++, i++) {
+		dest = (void *)start + *start;
+
+		pr_devel("patching dest %lx\n", (unsigned long)dest);
+
+		patch_instruction(dest, instrs[0]);
+
+		if (types & STF_BARRIER_FALLBACK)
+			patch_branch(dest + 1, (unsigned long)&stf_barrier_fallback,
+				     BRANCH_SET_LINK);
+		else
+			patch_instruction(dest + 1, instrs[1]);
+
+		patch_instruction(dest + 2, instrs[2]);
+	}
+
+	printk(KERN_DEBUG "stf-barrier: patched %d entry locations (%s barrier)\n", i,
+		(types == STF_BARRIER_NONE)                  ? "no" :
+		(types == STF_BARRIER_FALLBACK)              ? "fallback" :
+		(types == STF_BARRIER_EIEIO)                 ? "eieio" :
+		(types == (STF_BARRIER_SYNC_ORI))            ? "hwsync"
+		                                           : "unknown");
+}
+
+void do_stf_exit_barrier_fixups(enum stf_barrier_type types)
+{
+	unsigned int instrs[6], *dest;
+	long *start, *end;
+	int i;
+
+	start = PTRRELOC(&__start___stf_exit_barrier_fixup),
+	end = PTRRELOC(&__stop___stf_exit_barrier_fixup);
+
+	instrs[0] = 0x60000000; /* nop */
+	instrs[1] = 0x60000000; /* nop */
+	instrs[2] = 0x60000000; /* nop */
+	instrs[3] = 0x60000000; /* nop */
+	instrs[4] = 0x60000000; /* nop */
+	instrs[5] = 0x60000000; /* nop */
+
+	i = 0;
+	if (types & STF_BARRIER_FALLBACK || types & STF_BARRIER_SYNC_ORI) {
+		if (cpu_has_feature(CPU_FTR_HVMODE)) {
+			instrs[i++] = 0x7db14ba6; /* mtspr 0x131, r13 (HSPRG1) */
+			instrs[i++] = 0x7db04aa6; /* mfspr r13, 0x130 (HSPRG0) */
+		} else {
+			instrs[i++] = 0x7db243a6; /* mtsprg 2,r13	*/
+			instrs[i++] = 0x7db142a6; /* mfsprg r13,1    */
+	        }
+		instrs[i++] = 0x7c0004ac; /* hwsync		*/
+		instrs[i++] = 0xe9ad0000; /* ld r13,0(r13)	*/
+		instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */
+		if (cpu_has_feature(CPU_FTR_HVMODE)) {
+			instrs[i++] = 0x7db14aa6; /* mfspr r13, 0x131 (HSPRG1) */
+		} else {
+			instrs[i++] = 0x7db242a6; /* mfsprg r13,2 */
+		}
+	} else if (types & STF_BARRIER_EIEIO) {
+		instrs[i++] = 0x7e0006ac; /* eieio + bit 6 hint */
+	}
+
+	for (i = 0; start < end; start++, i++) {
+		dest = (void *)start + *start;
+
+		pr_devel("patching dest %lx\n", (unsigned long)dest);
+
+		patch_instruction(dest, instrs[0]);
+		patch_instruction(dest + 1, instrs[1]);
+		patch_instruction(dest + 2, instrs[2]);
+		patch_instruction(dest + 3, instrs[3]);
+		patch_instruction(dest + 4, instrs[4]);
+		patch_instruction(dest + 5, instrs[5]);
+	}
+	printk(KERN_DEBUG "stf-barrier: patched %d exit locations (%s barrier)\n", i,
+		(types == STF_BARRIER_NONE)                  ? "no" :
+		(types == STF_BARRIER_FALLBACK)              ? "fallback" :
+		(types == STF_BARRIER_EIEIO)                 ? "eieio" :
+		(types == (STF_BARRIER_SYNC_ORI))            ? "hwsync"
+		                                           : "unknown");
+}
+
+
+void do_stf_barrier_fixups(enum stf_barrier_type types)
+{
+	do_stf_entry_barrier_fixups(types);
+	do_stf_exit_barrier_fixups(types);
+}
+
 void do_rfi_flush_fixups(enum l1d_flush_type types)
 {
 	unsigned int instrs[3], *dest;
diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index 2c646f5bd144..17203abf38e8 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -130,6 +130,7 @@ static void __init pnv_setup_arch(void)
 	set_arch_panic_timeout(10, ARCH_PANIC_TIMEOUT);
 
 	pnv_setup_rfi_flush();
+	setup_stf_barrier();
 
 	/* Initialize SMP */
 	pnv_smp_init();
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 7349c05032be..91ade7755823 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -545,6 +545,7 @@ static void __init pSeries_setup_arch(void)
 	fwnmi_init();
 
 	pseries_setup_rfi_flush();
+	setup_stf_barrier();
 
 	/* By default, only probe PCI (can be overridden by rtas_pci) */
 	pci_add_flags(PCI_PROBE_ONLY);
-- 
2.14.1