1 files changed, 66 insertions, 71 deletions

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index f447c4a36f69..ea5dc7c90f46 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -78,47 +78,76 @@ static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
 }
 
 /*
- * Turn on the call to ftrace_caller() in instrumented function
+ * Find the address the callsite must branch to in order to reach '*addr'.
+ *
+ * Due to the limited range of 'BL' instructions, modules may be placed too far
+ * away to branch directly and must use a PLT.
+ *
+ * Returns true when '*addr' contains a reachable target address, or has been
+ * modified to contain a PLT address. Returns false otherwise.
  */
-int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
+				      struct module *mod,
+				      unsigned long *addr)
 {
 	unsigned long pc = rec->ip;
-	u32 old, new;
-	long offset = (long)pc - (long)addr;
+	long offset = (long)*addr - (long)pc;
+	struct plt_entry *plt;
 
-	if (offset < -SZ_128M || offset >= SZ_128M) {
-		struct module *mod;
-		struct plt_entry *plt;
+	/*
+	 * When the target is within range of the 'BL' instruction, use 'addr'
+	 * as-is and branch to that directly.
+	 */
+	if (offset >= -SZ_128M && offset < SZ_128M)
+		return true;
 
-		if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
-			return -EINVAL;
+	/*
+	 * When the target is outside of the range of a 'BL' instruction, we
+	 * must use a PLT to reach it. We can only place PLTs for modules, and
+	 * only when module PLT support is built-in.
+	 */
+	if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
+		return false;
 
-		/*
-		 * On kernels that support module PLTs, the offset between the
-		 * branch instruction and its target may legally exceed the
-		 * range of an ordinary relative 'bl' opcode. In this case, we
-		 * need to branch via a trampoline in the module.
-		 *
-		 * NOTE: __module_text_address() must be called with preemption
-		 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
-		 * retains its validity throughout the remainder of this code.
-		 */
+	/*
+	 * 'mod' is only set at module load time, but if we end up
+	 * dealing with an out-of-range condition, we can assume it
+	 * is due to a module being loaded far away from the kernel.
+	 *
+	 * NOTE: __module_text_address() must be called with preemption
+	 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
+	 * retains its validity throughout the remainder of this code.
+	 */
+	if (!mod) {
 		preempt_disable();
 		mod = __module_text_address(pc);
 		preempt_enable();
+	}
 
-		if (WARN_ON(!mod))
-			return -EINVAL;
+	if (WARN_ON(!mod))
+		return false;
 
-		plt = get_ftrace_plt(mod, addr);
-		if (!plt) {
-			pr_err("ftrace: no module PLT for %ps\n", (void *)addr);
-			return -EINVAL;
-		}
-
-		addr = (unsigned long)plt;
+	plt = get_ftrace_plt(mod, *addr);
+	if (!plt) {
+		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
+		return false;
 	}
 
+	*addr = (unsigned long)plt;
+	return true;
+}
+
+/*
+ * Turn on the call to ftrace_caller() in instrumented function
+ */
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+	unsigned long pc = rec->ip;
+	u32 old, new;
+
+	if (!ftrace_find_callable_addr(rec, NULL, &addr))
+		return -EINVAL;
+
 	old = aarch64_insn_gen_nop();
 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 
@@ -132,6 +161,11 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	unsigned long pc = rec->ip;
 	u32 old, new;
 
+	if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
+		return -EINVAL;
+	if (!ftrace_find_callable_addr(rec, NULL, &addr))
+		return -EINVAL;
+
 	old = aarch64_insn_gen_branch_imm(pc, old_addr,
 					  AARCH64_INSN_BRANCH_LINK);
 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
@@ -181,54 +215,15 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 		    unsigned long addr)
 {
 	unsigned long pc = rec->ip;
-	bool validate = true;
 	u32 old = 0, new;
-	long offset = (long)pc - (long)addr;
 
-	if (offset < -SZ_128M || offset >= SZ_128M) {
-		u32 replaced;
-
-		if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
-			return -EINVAL;
-
-		/*
-		 * 'mod' is only set at module load time, but if we end up
-		 * dealing with an out-of-range condition, we can assume it
-		 * is due to a module being loaded far away from the kernel.
-		 */
-		if (!mod) {
-			preempt_disable();
-			mod = __module_text_address(pc);
-			preempt_enable();
-
-			if (WARN_ON(!mod))
-				return -EINVAL;
-		}
-
-		/*
-		 * The instruction we are about to patch may be a branch and
-		 * link instruction that was redirected via a PLT entry. In
-		 * this case, the normal validation will fail, but we can at
-		 * least check that we are dealing with a branch and link
-		 * instruction that points into the right module.
-		 */
-		if (aarch64_insn_read((void *)pc, &replaced))
-			return -EFAULT;
-
-		if (!aarch64_insn_is_bl(replaced) ||
-		    !within_module(pc + aarch64_get_branch_offset(replaced),
-				   mod))
-			return -EINVAL;
-
-		validate = false;
-	} else {
-		old = aarch64_insn_gen_branch_imm(pc, addr,
-						  AARCH64_INSN_BRANCH_LINK);
-	}
+	if (!ftrace_find_callable_addr(rec, mod, &addr))
+		return -EINVAL;
 
+	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 	new = aarch64_insn_gen_nop();
 
-	return ftrace_modify_code(pc, old, new, validate);
+	return ftrace_modify_code(pc, old, new, true);
 }
 
 void arch_ftrace_update_code(int command)