Merge branch kvm-arm64/nvhe-stacktrace into kvmarm-master/next

* kvm-arm64/nvhe-stacktrace: (27 commits)
  : .
  : Add an overflow stack to the nVHE EL2 code, allowing
  : the implementation of an unwinder, courtesy of
  : Kalesh Singh. From the cover letter (slightly edited):
  :
  : "nVHE has two modes of operation: protected (pKVM) and unprotected
  : (conventional nVHE). Depending on the mode, a slightly different approach
  : is used to dump the hypervisor stacktrace but the core unwinding logic
  : remains the same.
  :
  : * Protected nVHE (pKVM) stacktraces:
  :
  : In protected nVHE mode, the host cannot directly access hypervisor memory.
  :
  : The hypervisor stack unwinding happens in EL2 and is made accessible to
  : the host via a shared buffer. Symbolizing and printing the stacktrace
  : addresses is delegated to the host and happens in EL1.
  :
  : * Non-protected (Conventional) nVHE stacktraces:
  :
  : In non-protected mode, the host is able to directly access the hypervisor
  : stack pages.
  :
  : The hypervisor stack unwinding and dumping of the stacktrace is performed
  : by the host in EL1, as this avoids the memory overhead of setting up
  : shared buffers between the host and hypervisor."
  :
  : Additional patches from Oliver Upton and Marc Zyngier, tidying up
  : the initial series.
  : .
  arm64: Update 'unwinder howto'
  KVM: arm64: Don't open code ARRAY_SIZE()
  KVM: arm64: Move nVHE-only helpers into kvm/stacktrace.c
  KVM: arm64: Make unwind()/on_accessible_stack() per-unwinder functions
  KVM: arm64: Move nVHE stacktrace unwinding into its own compilation unit
  KVM: arm64: Move PROTECTED_NVHE_STACKTRACE around
  KVM: arm64: Introduce pkvm_dump_backtrace()
  KVM: arm64: Implement protected nVHE hyp stack unwinder
  KVM: arm64: Save protected-nVHE (pKVM) hyp stacktrace
  KVM: arm64: Stub implementation of pKVM HYP stack unwinder
  KVM: arm64: Allocate shared pKVM hyp stacktrace buffers
  KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig
  KVM: arm64: Introduce hyp_dump_backtrace()
  KVM: arm64: Implement non-protected nVHE hyp stack unwinder
  KVM: arm64: Prepare non-protected nVHE hypervisor stacktrace
  KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder
  KVM: arm64: On stack overflow switch to hyp overflow_stack
  arm64: stacktrace: Add description of stacktrace/common.h
  arm64: stacktrace: Factor out common unwind()
  arm64: stacktrace: Handle frame pointer from different address spaces
  ...

Signed-off-by: Marc Zyngier <maz@kernel.org>

5 files changed, 280 insertions, 60 deletions

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 2e277f2ed671..53035763e48e 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -176,6 +176,22 @@ struct kvm_nvhe_init_params {
 	unsigned long vtcr;
 };
 
+/*
+ * Used by the host in EL1 to dump the nVHE hypervisor backtrace on
+ * hyp_panic() in non-protected mode.
+ *
+ * @stack_base:                 hyp VA of the hyp_stack base.
+ * @overflow_stack_base:        hyp VA of the hyp_overflow_stack base.
+ * @fp:                         hyp FP where the backtrace begins.
+ * @pc:                         hyp PC where the backtrace begins.
+ */
+struct kvm_nvhe_stacktrace_info {
+	unsigned long stack_base;
+	unsigned long overflow_stack_base;
+	unsigned long fp;
+	unsigned long pc;
+};
+
 /* Translate a kernel address @ptr into its equivalent linear mapping */
 #define kvm_ksym_ref(ptr)						\
 	({								\
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 0af70d9abede..cab80a9a4086 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -114,6 +114,14 @@
 #define OVERFLOW_STACK_SIZE	SZ_4K
 
 /*
+ * With the minimum frame size of [x29, x30], exactly half the combined
+ * sizes of the hyp and overflow stacks is the maximum size needed to
+ * save the unwinded stacktrace; plus an additional entry to delimit the
+ * end.
+ */
+#define NVHE_STACKTRACE_SIZE	((OVERFLOW_STACK_SIZE + PAGE_SIZE) / 2 + sizeof(long))
+
+/*
  * Alignment of kernel segments (e.g. .text, .data).
  *
  *  4 KB granule:  16 level 3 entries, with contiguous bit
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index aec9315bf156..6ebdcdff77f5 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -8,52 +8,20 @@
 #include <linux/percpu.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
-#include <linux/types.h>
 #include <linux/llist.h>
 
 #include <asm/memory.h>
+#include <asm/pointer_auth.h>
 #include <asm/ptrace.h>
 #include <asm/sdei.h>
 
-enum stack_type {
-	STACK_TYPE_UNKNOWN,
-	STACK_TYPE_TASK,
-	STACK_TYPE_IRQ,
-	STACK_TYPE_OVERFLOW,
-	STACK_TYPE_SDEI_NORMAL,
-	STACK_TYPE_SDEI_CRITICAL,
-	__NR_STACK_TYPES
-};
-
-struct stack_info {
-	unsigned long low;
-	unsigned long high;
-	enum stack_type type;
-};
+#include <asm/stacktrace/common.h>
 
 extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 			   const char *loglvl);
 
 DECLARE_PER_CPU(unsigned long *, irq_stack_ptr);
 
-static inline bool on_stack(unsigned long sp, unsigned long size,
-			    unsigned long low, unsigned long high,
-			    enum stack_type type, struct stack_info *info)
-{
-	if (!low)
-		return false;
-
-	if (sp < low || sp + size < sp || sp + size > high)
-		return false;
-
-	if (info) {
-		info->low = low;
-		info->high = high;
-		info->type = type;
-	}
-	return true;
-}
-
 static inline bool on_irq_stack(unsigned long sp, unsigned long size,
 				struct stack_info *info)
 {
@@ -89,30 +57,4 @@ static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
 			struct stack_info *info) { return false; }
 #endif
 
-
-/*
- * We can only safely access per-cpu stacks from current in a non-preemptible
- * context.
- */
-static inline bool on_accessible_stack(const struct task_struct *tsk,
-				       unsigned long sp, unsigned long size,
-				       struct stack_info *info)
-{
-	if (info)
-		info->type = STACK_TYPE_UNKNOWN;
-
-	if (on_task_stack(tsk, sp, size, info))
-		return true;
-	if (tsk != current || preemptible())
-		return false;
-	if (on_irq_stack(sp, size, info))
-		return true;
-	if (on_overflow_stack(sp, size, info))
-		return true;
-	if (on_sdei_stack(sp, size, info))
-		return true;
-
-	return false;
-}
-
 #endif	/* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
new file mode 100644
index 000000000000..f58eb944c46f
--- /dev/null
+++ b/arch/arm64/include/asm/stacktrace/common.h
@@ -0,0 +1,199 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Common arm64 stack unwinder code.
+ *
+ * To implement a new arm64 stack unwinder:
+ *     1) Include this header
+ *
+ *     2) Call into unwind_next_common() from your top level unwind
+ *        function, passing it the validation and translation callbacks
+ *        (though the later can be NULL if no translation is required).
+ *
+ * See: arch/arm64/kernel/stacktrace.c for the reference implementation.
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ */
+#ifndef __ASM_STACKTRACE_COMMON_H
+#define __ASM_STACKTRACE_COMMON_H
+
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/kprobes.h>
+#include <linux/types.h>
+
+enum stack_type {
+	STACK_TYPE_UNKNOWN,
+	STACK_TYPE_TASK,
+	STACK_TYPE_IRQ,
+	STACK_TYPE_OVERFLOW,
+	STACK_TYPE_SDEI_NORMAL,
+	STACK_TYPE_SDEI_CRITICAL,
+	STACK_TYPE_HYP,
+	__NR_STACK_TYPES
+};
+
+struct stack_info {
+	unsigned long low;
+	unsigned long high;
+	enum stack_type type;
+};
+
+/*
+ * A snapshot of a frame record or fp/lr register values, along with some
+ * accounting information necessary for robust unwinding.
+ *
+ * @fp:          The fp value in the frame record (or the real fp)
+ * @pc:          The lr value in the frame record (or the real lr)
+ *
+ * @stacks_done: Stacks which have been entirely unwound, for which it is no
+ *               longer valid to unwind to.
+ *
+ * @prev_fp:     The fp that pointed to this frame record, or a synthetic value
+ *               of 0. This is used to ensure that within a stack, each
+ *               subsequent frame record is at an increasing address.
+ * @prev_type:   The type of stack this frame record was on, or a synthetic
+ *               value of STACK_TYPE_UNKNOWN. This is used to detect a
+ *               transition from one stack to another.
+ *
+ * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
+ *               associated with the most recently encountered replacement lr
+ *               value.
+ *
+ * @task:        The task being unwound.
+ */
+struct unwind_state {
+	unsigned long fp;
+	unsigned long pc;
+	DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
+	unsigned long prev_fp;
+	enum stack_type prev_type;
+#ifdef CONFIG_KRETPROBES
+	struct llist_node *kr_cur;
+#endif
+	struct task_struct *task;
+};
+
+static inline bool on_stack(unsigned long sp, unsigned long size,
+			    unsigned long low, unsigned long high,
+			    enum stack_type type, struct stack_info *info)
+{
+	if (!low)
+		return false;
+
+	if (sp < low || sp + size < sp || sp + size > high)
+		return false;
+
+	if (info) {
+		info->low = low;
+		info->high = high;
+		info->type = type;
+	}
+	return true;
+}
+
+static inline void unwind_init_common(struct unwind_state *state,
+				      struct task_struct *task)
+{
+	state->task = task;
+#ifdef CONFIG_KRETPROBES
+	state->kr_cur = NULL;
+#endif
+
+	/*
+	 * Prime the first unwind.
+	 *
+	 * In unwind_next() we'll check that the FP points to a valid stack,
+	 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
+	 * treated as a transition to whichever stack that happens to be. The
+	 * prev_fp value won't be used, but we set it to 0 such that it is
+	 * definitely not an accessible stack address.
+	 */
+	bitmap_zero(state->stacks_done, __NR_STACK_TYPES);
+	state->prev_fp = 0;
+	state->prev_type = STACK_TYPE_UNKNOWN;
+}
+
+/*
+ * stack_trace_translate_fp_fn() - Translates a non-kernel frame pointer to
+ * a kernel address.
+ *
+ * @fp:   the frame pointer to be updated to its kernel address.
+ * @type: the stack type associated with frame pointer @fp
+ *
+ * Returns true and success and @fp is updated to the corresponding
+ * kernel virtual address; otherwise returns false.
+ */
+typedef bool (*stack_trace_translate_fp_fn)(unsigned long *fp,
+					    enum stack_type type);
+
+/*
+ * on_accessible_stack_fn() - Check whether a stack range is on any
+ * of the possible stacks.
+ *
+ * @tsk:  task whose stack is being unwound
+ * @sp:   stack address being checked
+ * @size: size of the stack range being checked
+ * @info: stack unwinding context
+ */
+typedef bool (*on_accessible_stack_fn)(const struct task_struct *tsk,
+				       unsigned long sp, unsigned long size,
+				       struct stack_info *info);
+
+static inline int unwind_next_common(struct unwind_state *state,
+				     struct stack_info *info,
+				     on_accessible_stack_fn accessible,
+				     stack_trace_translate_fp_fn translate_fp)
+{
+	unsigned long fp = state->fp, kern_fp = fp;
+	struct task_struct *tsk = state->task;
+
+	if (fp & 0x7)
+		return -EINVAL;
+
+	if (!accessible(tsk, fp, 16, info))
+		return -EINVAL;
+
+	if (test_bit(info->type, state->stacks_done))
+		return -EINVAL;
+
+	/*
+	 * If fp is not from the current address space perform the necessary
+	 * translation before dereferencing it to get the next fp.
+	 */
+	if (translate_fp && !translate_fp(&kern_fp, info->type))
+		return -EINVAL;
+
+	/*
+	 * As stacks grow downward, any valid record on the same stack must be
+	 * at a strictly higher address than the prior record.
+	 *
+	 * Stacks can nest in several valid orders, e.g.
+	 *
+	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
+	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
+	 * HYP -> OVERFLOW
+	 *
+	 * ... but the nesting itself is strict. Once we transition from one
+	 * stack to another, it's never valid to unwind back to that first
+	 * stack.
+	 */
+	if (info->type == state->prev_type) {
+		if (fp <= state->prev_fp)
+			return -EINVAL;
+	} else {
+		__set_bit(state->prev_type, state->stacks_done);
+	}
+
+	/*
+	 * Record this frame record's values and location. The prev_fp and
+	 * prev_type are only meaningful to the next unwind_next() invocation.
+	 */
+	state->fp = READ_ONCE(*(unsigned long *)(kern_fp));
+	state->pc = READ_ONCE(*(unsigned long *)(kern_fp + 8));
+	state->prev_fp = fp;
+	state->prev_type = info->type;
+
+	return 0;
+}
+
+#endif	/* __ASM_STACKTRACE_COMMON_H */
diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
new file mode 100644
index 000000000000..d5527b600390
--- /dev/null
+++ b/arch/arm64/include/asm/stacktrace/nvhe.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * KVM nVHE hypervisor stack tracing support.
+ *
+ * The unwinder implementation depends on the nVHE mode:
+ *
+ *   1) Non-protected nVHE mode - the host can directly access the
+ *      HYP stack pages and unwind the HYP stack in EL1. This saves having
+ *      to allocate shared buffers for the host to read the unwinded
+ *      stacktrace.
+ *
+ *   2) pKVM (protected nVHE) mode - the host cannot directly access
+ *      the HYP memory. The stack is unwinded in EL2 and dumped to a shared
+ *      buffer where the host can read and print the stacktrace.
+ *
+ * Copyright (C) 2022 Google LLC
+ */
+#ifndef __ASM_STACKTRACE_NVHE_H
+#define __ASM_STACKTRACE_NVHE_H
+
+#include <asm/stacktrace/common.h>
+
+/*
+ * kvm_nvhe_unwind_init - Start an unwind from the given nVHE HYP fp and pc
+ *
+ * @state : unwind_state to initialize
+ * @fp    : frame pointer at which to start the unwinding.
+ * @pc    : program counter at which to start the unwinding.
+ */
+static inline void kvm_nvhe_unwind_init(struct unwind_state *state,
+					unsigned long fp,
+					unsigned long pc)
+{
+	unwind_init_common(state, NULL);
+
+	state->fp = fp;
+	state->pc = pc;
+}
+
+#ifndef __KVM_NVHE_HYPERVISOR__
+/*
+ * Conventional (non-protected) nVHE HYP stack unwinder
+ *
+ * In non-protected mode, the unwinding is done from kernel proper context
+ * (by the host in EL1).
+ */
+
+DECLARE_KVM_NVHE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack);
+DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_stacktrace_info, kvm_stacktrace_info);
+DECLARE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+
+void kvm_nvhe_dump_backtrace(unsigned long hyp_offset);
+
+#endif	/* __KVM_NVHE_HYPERVISOR__ */
+#endif	/* __ASM_STACKTRACE_NVHE_H */