arm64: Add uprobe support

This patch adds support for uprobe on ARM64 architecture.

Unit tests for following have been done so far and they have been found
working
    1. Step-able instructions, like sub, ldr, add etc.
    2. Simulation-able like ret, cbnz, cbz etc.
    3. uretprobe
    4. Reject-able instructions like sev, wfe etc.
    5. trapped and abort xol path
    6. probe at unaligned user address.
    7. longjump test cases

Currently it does not support aarch32 instruction probing.

Signed-off-by: Pratyush Anand <panand@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 218 insertions, 0 deletions

diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
index ce06312e3d34..89b6df613dde 100644
--- a/arch/arm64/kernel/probes/Makefile
+++ b/arch/arm64/kernel/probes/Makefile
@@ -1,3 +1,5 @@
 obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o	\
 				   kprobes_trampoline.o		\
 				   simulate-insn.o
+obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o	\
+				   simulate-insn.o
diff --git a/arch/arm64/kernel/probes/uprobes.c b/arch/arm64/kernel/probes/uprobes.c
new file mode 100644
index 000000000000..26c998534dca
--- /dev/null
+++ b/arch/arm64/kernel/probes/uprobes.c
@@ -0,0 +1,216 @@
+/*
+ * Copyright (C) 2014-2016 Pratyush Anand <panand@redhat.com>
+ *
+ * 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.
+ */
+#include <linux/highmem.h>
+#include <linux/ptrace.h>
+#include <linux/uprobes.h>
+#include <asm/cacheflush.h>
+
+#include "decode-insn.h"
+
+#define UPROBE_INV_FAULT_CODE	UINT_MAX
+
+void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+		void *src, unsigned long len)
+{
+	void *xol_page_kaddr = kmap_atomic(page);
+	void *dst = xol_page_kaddr + (vaddr & ~PAGE_MASK);
+
+	/* Initialize the slot */
+	memcpy(dst, src, len);
+
+	/* flush caches (dcache/icache) */
+	sync_icache_aliases(dst, len);
+
+	kunmap_atomic(xol_page_kaddr);
+}
+
+unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
+{
+	return instruction_pointer(regs);
+}
+
+int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
+		unsigned long addr)
+{
+	probe_opcode_t insn;
+
+	/* TODO: Currently we do not support AARCH32 instruction probing */
+	if (test_bit(TIF_32BIT, &mm->context.flags))
+		return -ENOTSUPP;
+	else if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
+		return -EINVAL;
+
+	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
+
+	switch (arm_probe_decode_insn(insn, &auprobe->api)) {
+	case INSN_REJECTED:
+		return -EINVAL;
+
+	case INSN_GOOD_NO_SLOT:
+		auprobe->simulate = true;
+		break;
+
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	/* Initialize with an invalid fault code to detect if ol insn trapped */
+	current->thread.fault_code = UPROBE_INV_FAULT_CODE;
+
+	/* Instruction points to execute ol */
+	instruction_pointer_set(regs, utask->xol_vaddr);
+
+	user_enable_single_step(current);
+
+	return 0;
+}
+
+int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	WARN_ON_ONCE(current->thread.fault_code != UPROBE_INV_FAULT_CODE);
+
+	/* Instruction points to execute next to breakpoint address */
+	instruction_pointer_set(regs, utask->vaddr + 4);
+
+	user_disable_single_step(current);
+
+	return 0;
+}
+bool arch_uprobe_xol_was_trapped(struct task_struct *t)
+{
+	/*
+	 * Between arch_uprobe_pre_xol and arch_uprobe_post_xol, if an xol
+	 * insn itself is trapped, then detect the case with the help of
+	 * invalid fault code which is being set in arch_uprobe_pre_xol
+	 */
+	if (t->thread.fault_code != UPROBE_INV_FAULT_CODE)
+		return true;
+
+	return false;
+}
+
+bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	probe_opcode_t insn;
+	unsigned long addr;
+
+	if (!auprobe->simulate)
+		return false;
+
+	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
+	addr = instruction_pointer(regs);
+
+	if (auprobe->api.handler)
+		auprobe->api.handler(insn, addr, regs);
+
+	return true;
+}
+
+void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	/*
+	 * Task has received a fatal signal, so reset back to probbed
+	 * address.
+	 */
+	instruction_pointer_set(regs, utask->vaddr);
+
+	user_disable_single_step(current);
+}
+
+bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
+		struct pt_regs *regs)
+{
+	/*
+	 * If a simple branch instruction (B) was called for retprobed
+	 * assembly label then return true even when regs->sp and ret->stack
+	 * are same. It will ensure that cleanup and reporting of return
+	 * instances corresponding to callee label is done when
+	 * handle_trampoline for called function is executed.
+	 */
+	if (ctx == RP_CHECK_CHAIN_CALL)
+		return regs->sp <= ret->stack;
+	else
+		return regs->sp < ret->stack;
+}
+
+unsigned long
+arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,
+				  struct pt_regs *regs)
+{
+	unsigned long orig_ret_vaddr;
+
+	orig_ret_vaddr = procedure_link_pointer(regs);
+	/* Replace the return addr with trampoline addr */
+	procedure_link_pointer_set(regs, trampoline_vaddr);
+
+	return orig_ret_vaddr;
+}
+
+int arch_uprobe_exception_notify(struct notifier_block *self,
+				 unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
+
+static int uprobe_breakpoint_handler(struct pt_regs *regs,
+		unsigned int esr)
+{
+	if (user_mode(regs) && uprobe_pre_sstep_notifier(regs))
+		return DBG_HOOK_HANDLED;
+
+	return DBG_HOOK_ERROR;
+}
+
+static int uprobe_single_step_handler(struct pt_regs *regs,
+		unsigned int esr)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (user_mode(regs)) {
+		WARN_ON(utask &&
+			(instruction_pointer(regs) != utask->xol_vaddr + 4));
+
+		if (uprobe_post_sstep_notifier(regs))
+			return DBG_HOOK_HANDLED;
+	}
+
+	return DBG_HOOK_ERROR;
+}
+
+/* uprobe breakpoint handler hook */
+static struct break_hook uprobes_break_hook = {
+	.esr_mask = BRK64_ESR_MASK,
+	.esr_val = BRK64_ESR_UPROBES,
+	.fn = uprobe_breakpoint_handler,
+};
+
+/* uprobe single step handler hook */
+static struct step_hook uprobes_step_hook = {
+	.fn = uprobe_single_step_handler,
+};
+
+static int __init arch_init_uprobes(void)
+{
+	register_break_hook(&uprobes_break_hook);
+	register_step_hook(&uprobes_step_hook);
+
+	return 0;
+}
+
+device_initcall(arch_init_uprobes);