[v4.4,18/45] arm64: Add skeleton to harden the branch predictor against aliasing attacks

Message ID 1b43c981c345cd203f08bfa850e64c9e5806c4b8.1560480942.git.viresh.kumar@linaro.org
State Superseded
Headers show
Series
  • V4.4 backport of arm64 Spectre patches
Related show

Commit Message

Viresh Kumar June 14, 2019, 3:08 a.m.
From: Will Deacon <will.deacon@arm.com>


commit 0f15adbb2861ce6f75ccfc5a92b19eae0ef327d0 upstream.

Aliasing attacks against CPU branch predictors can allow an attacker to
redirect speculative control flow on some CPUs and potentially divulge
information from one context to another.

This patch adds initial skeleton code behind a new Kconfig option to
enable implementation-specific mitigations against these attacks for
CPUs that are affected.

Co-developed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

[ v4.4: Changes made according to 4.4 codebase ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

---
 arch/arm64/Kconfig                  | 17 +++++++
 arch/arm64/include/asm/cpufeature.h |  3 +-
 arch/arm64/include/asm/mmu.h        | 39 +++++++++++++++
 arch/arm64/include/asm/sysreg.h     |  2 +
 arch/arm64/kernel/Makefile          |  5 ++
 arch/arm64/kernel/bpi.S             | 55 +++++++++++++++++++++
 arch/arm64/kernel/cpu_errata.c      | 74 +++++++++++++++++++++++++++++
 arch/arm64/kernel/cpufeature.c      |  3 +-
 arch/arm64/kernel/entry.S           |  8 ++--
 arch/arm64/mm/context.c             |  2 +
 arch/arm64/mm/fault.c               | 16 +++++++
 11 files changed, 219 insertions(+), 5 deletions(-)
 create mode 100644 arch/arm64/kernel/bpi.S

-- 
2.21.0.rc0.269.g1a574e7a288b

Patch

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f18b8c26a959..5fa01073566b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -624,6 +624,23 @@  config FORCE_MAX_ZONEORDER
 	  However for 4K, we choose a higher default value, 11 as opposed to 10, giving us
 	  4M allocations matching the default size used by generic code.
 
+config HARDEN_BRANCH_PREDICTOR
+	bool "Harden the branch predictor against aliasing attacks" if EXPERT
+	default y
+	help
+	  Speculation attacks against some high-performance processors rely on
+	  being able to manipulate the branch predictor for a victim context by
+	  executing aliasing branches in the attacker context.  Such attacks
+	  can be partially mitigated against by clearing internal branch
+	  predictor state and limiting the prediction logic in some situations.
+
+	  This config option will take CPU-specific actions to harden the
+	  branch predictor against aliasing attacks and may rely on specific
+	  instruction sequences or control bits being set by the system
+	  firmware.
+
+	  If unsure, say Y.
+
 menuconfig ARMV8_DEPRECATED
 	bool "Emulate deprecated/obsolete ARMv8 instructions"
 	depends on COMPAT
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 4c31e14c0f0e..ff3753127a30 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -32,8 +32,9 @@ 
 #define ARM64_WORKAROUND_834220			7
 #define ARM64_WORKAROUND_CAVIUM_27456		8
 #define ARM64_HAS_32BIT_EL0			9
+#define ARM64_HARDEN_BRANCH_PREDICTOR		10
 
-#define ARM64_NCAPS				10
+#define ARM64_NCAPS				11
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 990124a67eeb..8d0129210416 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -16,6 +16,8 @@ 
 #ifndef __ASM_MMU_H
 #define __ASM_MMU_H
 
+#include <linux/percpu.h>
+
 typedef struct {
 	atomic64_t	id;
 	void		*vdso;
@@ -28,6 +30,43 @@  typedef struct {
  */
 #define ASID(mm)	((mm)->context.id.counter & 0xffff)
 
+typedef void (*bp_hardening_cb_t)(void);
+
+struct bp_hardening_data {
+	int			hyp_vectors_slot;
+	bp_hardening_cb_t	fn;
+};
+
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+extern char __bp_harden_hyp_vecs_start[], __bp_harden_hyp_vecs_end[];
+
+DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
+
+static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)
+{
+	return this_cpu_ptr(&bp_hardening_data);
+}
+
+static inline void arm64_apply_bp_hardening(void)
+{
+	struct bp_hardening_data *d;
+
+	if (!cpus_have_cap(ARM64_HARDEN_BRANCH_PREDICTOR))
+		return;
+
+	d = arm64_get_bp_hardening_data();
+	if (d->fn)
+		d->fn();
+}
+#else
+static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)
+{
+	return NULL;
+}
+
+static inline void arm64_apply_bp_hardening(void)	{ }
+#endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
+
 extern void paging_init(void);
 extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
 extern void init_mem_pgprot(void);
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 50150320f80d..523b089fb408 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -95,6 +95,8 @@ 
 #define ID_AA64ISAR0_AES_SHIFT		4
 
 /* id_aa64pfr0 */
+#define ID_AA64PFR0_CSV2_SHIFT		56
+#define ID_AA64PFR0_SVE_SHIFT		32
 #define ID_AA64PFR0_GIC_SHIFT		24
 #define ID_AA64PFR0_ASIMD_SHIFT		20
 #define ID_AA64PFR0_FP_SHIFT		16
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 474691f8b13a..aa8f28210219 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -42,7 +42,12 @@  arm64-obj-$(CONFIG_PCI)			+= pci.o
 arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
 arm64-obj-$(CONFIG_ACPI)		+= acpi.o
 
+ifeq ($(CONFIG_KVM),y)
+arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR)	+= bpi.o
+endif
+
 obj-y					+= $(arm64-obj-y) vdso/
+
 obj-m					+= $(arm64-obj-m)
 head-y					:= head.o
 extra-y					+= $(head-y) vmlinux.lds
diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
new file mode 100644
index 000000000000..06a931eb2673
--- /dev/null
+++ b/arch/arm64/kernel/bpi.S
@@ -0,0 +1,55 @@ 
+/*
+ * Contains CPU specific branch predictor invalidation sequences
+ *
+ * Copyright (C) 2018 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+
+.macro ventry target
+	.rept 31
+	nop
+	.endr
+	b	\target
+.endm
+
+.macro vectors target
+	ventry \target + 0x000
+	ventry \target + 0x080
+	ventry \target + 0x100
+	ventry \target + 0x180
+
+	ventry \target + 0x200
+	ventry \target + 0x280
+	ventry \target + 0x300
+	ventry \target + 0x380
+
+	ventry \target + 0x400
+	ventry \target + 0x480
+	ventry \target + 0x500
+	ventry \target + 0x580
+
+	ventry \target + 0x600
+	ventry \target + 0x680
+	ventry \target + 0x700
+	ventry \target + 0x780
+.endm
+
+	.align	11
+ENTRY(__bp_harden_hyp_vecs_start)
+	.rept 4
+	vectors __kvm_hyp_vector
+	.endr
+ENTRY(__bp_harden_hyp_vecs_end)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 0971d80d3623..6c5e9e462629 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -43,6 +43,80 @@  is_affected_midr_range(const struct arm64_cpu_capabilities *entry, int scope)
 	return (midr >= entry->midr_range_min && midr <= entry->midr_range_max);
 }
 
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+#include <asm/mmu_context.h>
+#include <asm/cacheflush.h>
+
+DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
+
+#ifdef CONFIG_KVM
+static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
+				const char *hyp_vecs_end)
+{
+	void *dst = __bp_harden_hyp_vecs_start + slot * SZ_2K;
+	int i;
+
+	for (i = 0; i < SZ_2K; i += 0x80)
+		memcpy(dst + i, hyp_vecs_start, hyp_vecs_end - hyp_vecs_start);
+
+	flush_icache_range((uintptr_t)dst, (uintptr_t)dst + SZ_2K);
+}
+
+static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
+				      const char *hyp_vecs_start,
+				      const char *hyp_vecs_end)
+{
+	static int last_slot = -1;
+	static DEFINE_SPINLOCK(bp_lock);
+	int cpu, slot = -1;
+
+	spin_lock(&bp_lock);
+	for_each_possible_cpu(cpu) {
+		if (per_cpu(bp_hardening_data.fn, cpu) == fn) {
+			slot = per_cpu(bp_hardening_data.hyp_vectors_slot, cpu);
+			break;
+		}
+	}
+
+	if (slot == -1) {
+		last_slot++;
+		BUG_ON(((__bp_harden_hyp_vecs_end - __bp_harden_hyp_vecs_start)
+			/ SZ_2K) <= last_slot);
+		slot = last_slot;
+		__copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end);
+	}
+
+	__this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot);
+	__this_cpu_write(bp_hardening_data.fn, fn);
+	spin_unlock(&bp_lock);
+}
+#else
+static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
+				      const char *hyp_vecs_start,
+				      const char *hyp_vecs_end)
+{
+	__this_cpu_write(bp_hardening_data.fn, fn);
+}
+#endif	/* CONFIG_KVM */
+
+static void  install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,
+				     bp_hardening_cb_t fn,
+				     const char *hyp_vecs_start,
+				     const char *hyp_vecs_end)
+{
+	u64 pfr0;
+
+	if (!entry->matches(entry, SCOPE_LOCAL_CPU))
+		return;
+
+	pfr0 = read_cpuid(ID_AA64PFR0_EL1);
+	if (cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_CSV2_SHIFT))
+		return;
+
+	__install_bp_hardening_cb(fn, hyp_vecs_start, hyp_vecs_end);
+}
+#endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
+
 #define MIDR_RANGE(model, min, max) \
 	.def_scope = SCOPE_LOCAL_CPU, \
 	.matches = is_affected_midr_range, \
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 79c1cd9f15c2..ab847c4fabcb 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -83,7 +83,8 @@  static struct arm64_ftr_bits ftr_id_aa64isar0[] = {
 };
 
 static struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
+	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV2_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 28, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e6aec982dea9..05bfc71639fc 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -495,13 +495,15 @@  ENDPROC(el1_irq)
 	 * Instruction abort handling
 	 */
 	mrs	x26, far_el1
-	// enable interrupts before calling the main handler
-	enable_dbg_and_irq
+	msr     daifclr, #(8 | 4 | 1)
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_off
+#endif
 	ct_user_exit
 	mov	x0, x26
 	orr	x1, x25, #1 << 24		// use reserved ISS bit for instruction aborts
 	mov	x2, sp
-	bl	do_mem_abort
+	bl	do_el0_ia_bp_hardening
 	b	ret_to_user
 el0_fpsimd_acc:
 	/*
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 492d2968fa8f..be42bd3dca5c 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -193,6 +193,8 @@  asmlinkage void post_ttbr_update_workaround(void)
 			"ic iallu; dsb nsh; isb",
 			ARM64_WORKAROUND_CAVIUM_27456,
 			CONFIG_CAVIUM_ERRATUM_27456));
+
+	arm64_apply_bp_hardening();
 }
 
 static int asids_init(void)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 89abdf9af4e6..1878c881a247 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -535,6 +535,22 @@  asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
 	arm64_notify_die("", regs, &info, esr);
 }
 
+asmlinkage void __exception do_el0_ia_bp_hardening(unsigned long addr,
+						   unsigned int esr,
+						   struct pt_regs *regs)
+{
+	/*
+	 * We've taken an instruction abort from userspace and not yet
+	 * re-enabled IRQs. If the address is a kernel address, apply
+	 * BP hardening prior to enabling IRQs and pre-emption.
+	 */
+	if (addr > TASK_SIZE)
+		arm64_apply_bp_hardening();
+
+	local_irq_enable();
+	do_mem_abort(addr, esr, regs);
+}
+
 /*
  * Handle stack alignment exceptions.
  */