livepatch/powerpc: 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 ppc64/ppc32.
Signed-off-by: NYang Jihong <yangjihong1@huawei.com>
Signed-off-by: NLi Huafei <lihuafei1@huawei.com>
Reviewed-by: NXu Kuohai <xukuohai@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/powerpc/include/asm/livepatch.h

@@ -75,6 +75,7 @@ extern void livepatch_branch_stub_end(void);
 #ifdef PPC64_ELF_ABI_v1
 extern void livepatch_branch_trampoline(void);
 extern void livepatch_branch_trampoline_end(void);
+extern void livepatch_brk_trampoline(void);
 void livepatch_create_btramp(struct ppc64_klp_btramp_entry *entry, unsigned long addr);
 #else
 static inline void livepatch_create_btramp(struct ppc64_klp_btramp_entry *entry,
@@ -93,6 +94,12 @@ struct arch_klp_data {
 #else
 	unsigned long trampoline;
 #endif /* PPC64_ELF_ABI_v1 */
+
+	/*
+	 * Saved opcode at the entry of the old func (which maybe replaced
+	 * with breakpoint).
+	 */
+	u32 saved_opcode;
 };
 
 #elif defined(CONFIG_PPC32)
@@ -101,10 +108,23 @@ struct arch_klp_data {
 #define LJMP_INSN_SIZE	4
 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;
 };
 
 #endif	/* CONFIG_PPC64 */
 
+#ifdef PPC64_ELF_ABI_v1
+struct klp_func_node;
+void arch_klp_set_brk_func(struct klp_func_node *func_node, void *new_func);
+#endif
+int klp_brk_handler(struct pt_regs *regs);
+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 /* CONFIG_LIVEPATCH_FTRACE */

arch/powerpc/kernel/Makefile

@@ -95,7 +95,7 @@ obj-$(CONFIG_44x)		+= cpu_setup_44x.o
 obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o
 obj-$(CONFIG_PPC_DOORBELL)	+= dbell.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
-obj-$(CONFIG_LIVEPATCH_WO_FTRACE) += livepatch_$(BITS).o
+obj-$(CONFIG_LIVEPATCH_WO_FTRACE) += livepatch.o livepatch_$(BITS).o
 
 extra-$(CONFIG_PPC64)		:= head_64.o
 extra-$(CONFIG_PPC_BOOK3S_32)	:= head_book3s_32.o

arch/powerpc/kernel/entry_64.S

@@ -1068,5 +1068,41 @@ _GLOBAL(livepatch_branch_trampoline)
 	blr
 _GLOBAL(livepatch_branch_trampoline_end)
 	nop
+
+/*
+ * This function is the trampoline of livepatch brk handler.
+ *
+ * brk -> traps
+ *  - klp_brk_handler
+ *   - set R11 to new_func address
+ *   - set NIP to livepatch_brk_trampoline address
+ * see arch/powerpc/kernel/livepatch.c
+ */
+_GLOBAL(livepatch_brk_trampoline)
+	mflr	r0
+	std	r0, 16(r1)
+	std	r2, 24(r1)
+	stdu    r1, -STACK_FRAME_OVERHEAD(r1)
+
+	/* Call NEW_FUNC */
+	ld	r12, 0(r11)	/* load new func address to R12 */
+#ifdef PPC64_ELF_ABI_v1
+	ld	r2,  8(r11)	/* set up new R2 */
+#endif
+	mtctr   r12		/* load R12(new func address) to CTR */
+	bctrl			/* call new func */
+
+	/*
+	 * Now we are returning from the patched function to the original
+	 * caller A. We are free to use r11, r12 and we can use r2 until we
+	 * restore it.
+	 */
+	addi	r1, r1, STACK_FRAME_OVERHEAD
+	ld	r2, 24(r1)
+	ld	r0, 16(r1)
+	mtlr	r0
+
+	/* Return to original caller of live patched function */
+	blr
 #endif
 #endif /* CONFIG_LIVEPATCH_WO_FTRACE */

arch/powerpc/kernel/livepatch.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * livepatch.c - powerpc-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2022  Huawei Technologies Co., Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * 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/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/livepatch.h>
+#include <asm/probes.h>
+#include <asm/livepatch.h>
+#include <asm/code-patching.h>
+
+int arch_klp_add_breakpoint(struct arch_klp_data *arch_data, void *old_func)
+{
+	struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)old_func);
+
+	arch_data->saved_opcode = ppc_inst_val(insn);
+	patch_instruction((struct ppc_inst *)old_func, ppc_inst(BREAKPOINT_INSTRUCTION));
+	return 0;
+}
+
+void arch_klp_remove_breakpoint(struct arch_klp_data *arch_data, void *old_func)
+{
+	patch_instruction((struct ppc_inst *)old_func, ppc_inst(arch_data->saved_opcode));
+}
+
+int klp_brk_handler(struct pt_regs *regs)
+{
+	void *brk_func = NULL;
+	unsigned long addr = regs->nip;
+
+	if (user_mode(regs))
+		return 0;
+
+	brk_func = klp_get_brk_func((void *)addr);
+	if (!brk_func)
+		return 0;
+
+#ifdef PPC64_ELF_ABI_v1
+	/*
+	 * Only static trampoline can be used here to prevent
+	 * resource release caused by rollback.
+	 */
+	regs->gpr[PT_R11] = (unsigned long)brk_func;
+	regs->nip = ppc_function_entry((void *)livepatch_brk_trampoline);
+#else
+	regs->nip = (unsigned long)brk_func;
+#endif
+
+	return 1;
+}

arch/powerpc/kernel/traps.c

@@ -67,6 +67,9 @@
 #include <asm/kprobes.h>
 #include <asm/stacktrace.h>
 #include <asm/nmi.h>
+#ifdef CONFIG_LIVEPATCH_STOP_MACHINE_CONSISTENCY
+#include <asm/livepatch.h>
+#endif
 
 #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC_CORE)
 int (*__debugger)(struct pt_regs *regs) __read_mostly;
@@ -1491,6 +1494,11 @@ void program_check_exception(struct pt_regs *regs)
 		if (kprobe_handler(regs))
 			goto bail;
 
+#ifdef CONFIG_LIVEPATCH_STOP_MACHINE_CONSISTENCY
+		if (klp_brk_handler(regs))
+			goto bail;
+#endif
+
 		/* trap exception */
 		if (notify_die(DIE_BPT, "breakpoint", regs, 5, 5, SIGTRAP)
 				== NOTIFY_STOP)