livepatch/arm: Support breakpoint exception optimization

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5CJ7X

--------------------------------

Add breakpoint exception optimization support to improve livepatch
success rate for arm.
Signed-off-by: NYang Jihong <yangjihong1@huawei.com>
Reviewed-by: NXu Kuohai <xukuohai@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arm/include/asm/livepatch.h

@@ -23,6 +23,8 @@
 
 #include <linux/module.h>
 
+#define KLP_ARM_BREAKPOINT_INSTRUCTION		0xe7f001f9
+
 struct klp_patch;
 struct klp_func;
 
@@ -47,8 +49,16 @@ int klp_check_calltrace(struct klp_patch *patch, int enable);
 
 struct arch_klp_data {
 	u32 old_insns[LJMP_INSN_SIZE];
+
+	/*
+	 * Saved opcode at the entry of the old func (which maybe replaced
+	 * with breakpoint).
+	 */
+	u32 saved_opcode;
 };
 
+int arch_klp_add_breakpoint(struct arch_klp_data *arch_data, void *old_func);
+void arch_klp_remove_breakpoint(struct arch_klp_data *arch_data, void *old_func);
 long arch_klp_save_old_code(struct arch_klp_data *arch_data, void *old_func);
 
 #endif

arch/arm/kernel/livepatch.c

@@ -28,6 +28,8 @@
 #include <asm/stacktrace.h>
 #include <asm/cacheflush.h>
 #include <linux/slab.h>
+#include <linux/ptrace.h>
+#include <asm/traps.h>
 #include <asm/insn.h>
 #include <asm/patch.h>
 
@@ -317,6 +319,49 @@ int klp_check_calltrace(struct klp_patch *patch, int enable)
 	free_list(&check_funcs);
 	return ret;
 }
+
+int arch_klp_add_breakpoint(struct arch_klp_data *arch_data, void *old_func)
+{
+	u32 *addr = (u32 *)old_func;
+
+	arch_data->saved_opcode = le32_to_cpu(*addr);
+	patch_text(old_func, KLP_ARM_BREAKPOINT_INSTRUCTION);
+	return 0;
+}
+
+void arch_klp_remove_breakpoint(struct arch_klp_data *arch_data, void *old_func)
+{
+	patch_text(old_func, arch_data->saved_opcode);
+}
+
+static int klp_trap_handler(struct pt_regs *regs, unsigned int instr)
+{
+	void *brk_func = NULL;
+	unsigned long addr = regs->ARM_pc;
+
+	brk_func = klp_get_brk_func((void *)addr);
+	if (!brk_func) {
+		pr_warn("Unrecoverable livepatch detected.\n");
+		BUG();
+	}
+
+	regs->ARM_pc = (unsigned long)brk_func;
+	return 0;
+}
+
+static struct undef_hook klp_arm_break_hook = {
+	.instr_mask	= 0x0fffffff,
+	.instr_val	= (KLP_ARM_BREAKPOINT_INSTRUCTION & 0x0fffffff),
+	.cpsr_mask	= MODE_MASK,
+	.cpsr_val	= SVC_MODE,
+	.fn		= klp_trap_handler,
+};
+
+void arch_klp_init(void)
+{
+	register_undef_hook(&klp_arm_break_hook);
+}
+
 #endif
 
 static inline bool offset_in_range(unsigned long pc, unsigned long addr,