[PATCH v6 8/8] LoongArch: Add kernel livepatching support

[Tiezhu Yang]

The arch-specified function ftrace_regs_set_instruction_pointer() has been
implemented in arch/loongarch/include/asm/ftrace.h, so here only implement
arch_stack_walk_reliable() function.

Here are the test logs:

[root@linux fedora]# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-6.8.0-rc2 root=/dev/sda3
[root@linux fedora]# modprobe livepatch-sample
[root@linux fedora]# cat /proc/cmdline
this has been live patched

[root@linux fedora]# echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
[root@linux fedora]# rmmod livepatch_sample
[root@linux fedora]# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-6.8.0-rc2 root=/dev/sda3

[root@linux fedora]# dmesg -t | tail -5
livepatch: enabling patch 'livepatch_sample'
livepatch: 'livepatch_sample': starting patching transition
livepatch: 'livepatch_sample': patching complete
livepatch: 'livepatch_sample': starting unpatching transition
livepatch: 'livepatch_sample': unpatching complete

Co-developed-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 arch/loongarch/Kconfig                   |  4 +++
 arch/loongarch/include/asm/thread_info.h |  2 ++
 arch/loongarch/kernel/stacktrace.c       | 41 ++++++++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 17be0bff0f40..ecdc685daeea 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -132,6 +132,7 @@ config LOONGARCH
 	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_KVM
+	select HAVE_LIVEPATCH
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI
 	select HAVE_OBJTOOL if AS_HAS_EXPLICIT_RELOCS
@@ -141,6 +142,7 @@ config LOONGARCH
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_PREEMPT_DYNAMIC_KEY
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_RELIABLE_STACKTRACE if UNWINDER_ORC
 	select HAVE_RETHOOK
 	select HAVE_RSEQ
 	select HAVE_RUST
@@ -695,6 +697,8 @@ config KASAN_SHADOW_OFFSET
 	default 0x0
 	depends on KASAN
 
+source "kernel/livepatch/Kconfig"
+
 menu "Power management options"
 
 config ARCH_SUSPEND_POSSIBLE
diff --git a/arch/loongarch/include/asm/thread_info.h b/arch/loongarch/include/asm/thread_info.h
index 8cb653d49a54..8bf0e6f51546 100644
--- a/arch/loongarch/include/asm/thread_info.h
+++ b/arch/loongarch/include/asm/thread_info.h
@@ -86,6 +86,7 @@ register unsigned long current_stack_pointer __asm__("$sp");
 #define TIF_LASX_CTX_LIVE	18	/* LASX context must be preserved */
 #define TIF_USEDLBT		19	/* LBT was used by this task this quantum (SMP) */
 #define TIF_LBT_CTX_LIVE	20	/* LBT context must be preserved */
+#define TIF_PATCH_PENDING	21	/* pending live patching update */
 
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
@@ -105,6 +106,7 @@ register unsigned long current_stack_pointer __asm__("$sp");
 #define _TIF_LASX_CTX_LIVE	(1<<TIF_LASX_CTX_LIVE)
 #define _TIF_USEDLBT		(1<<TIF_USEDLBT)
 #define _TIF_LBT_CTX_LIVE	(1<<TIF_LBT_CTX_LIVE)
+#define _TIF_PATCH_PENDING	(1<<TIF_PATCH_PENDING)
 
 #endif /* __KERNEL__ */
 #endif /* _ASM_THREAD_INFO_H */
diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
index eaec82e02c92..8f4b217c9114 100644
--- a/arch/loongarch/kernel/stacktrace.c
+++ b/arch/loongarch/kernel/stacktrace.c
@@ -40,6 +40,47 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 	}
 }
 
+int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
+			     void *cookie, struct task_struct *task)
+{
+	unsigned long addr;
+	struct pt_regs dummyregs;
+	struct pt_regs *regs = &dummyregs;
+	struct unwind_state state;
+
+	if (task == current) {
+		regs->regs[3] = (unsigned long)__builtin_frame_address(0);
+		regs->csr_era = (unsigned long)__builtin_return_address(0);
+	} else {
+		regs->regs[3] = thread_saved_fp(task);
+		regs->csr_era = thread_saved_ra(task);
+	}
+	regs->regs[1] = 0;
+	regs->regs[22] = 0;
+
+	for (unwind_start(&state, task, regs);
+	     !unwind_done(&state) && !unwind_error(&state);
+	     unwind_next_frame(&state)) {
+		addr = unwind_get_return_address(&state);
+
+		/*
+		 * A NULL or invalid return address probably means there's some
+		 * generated code which __kernel_text_address() doesn't know about.
+		 */
+		if (!addr)
+			return -EINVAL;
+
+		if (!consume_entry(cookie, addr))
+			return -EINVAL;
+	}
+
+	/* Check for stack corruption */
+	if (unwind_error(&state))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int
 copy_stack_frame(unsigned long fp, struct stack_frame *frame)
 {
-- 
2.42.0