!250 add UPROBE_ALTER_PC flag for uprobe mechanism

Merge Pull Request from: @anatas 
 
[Description]
We try to implement a live-patch mechanism in the userspace based on the UPROBE.
In the handler, we may change the PC register.
In this case, UPROBE must skip the handle of the next instruction.

[Testing]
kernel options:
UPROBES_SUPPORT_PC_ALTER=y

 
 
Link:https://gitee.com/openeuler/kernel/pulls/250 
Reviewed-by: Xu Kuohai <xukuohai@huawei.com> 
Reviewed-by: Liu Chao <liuchao173@huawei.com> 
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com> 
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> 

arch/Kconfig

@@ -156,6 +156,15 @@ config UPROBES
 	    managed by the kernel and kept transparent to the probed
 	    application. )
 
+config UPROBES_SUPPORT_PC_ALTER
+	def_bool n
+	depends on UPROBES
+	help
+	  Add UPROBE_ALTER_PC flag for uprobe handlers. When handlers
+	  change the pc register, set this flag to let the uprobe
+	  mechanism skip the execuation of the next insturction.
+
+
 config HAVE_64BIT_ALIGNED_ACCESS
 	def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 	help

arch/x86/configs/openeuler_defconfig

@@ -758,6 +758,7 @@ CONFIG_JUMP_LABEL=y
 CONFIG_OPTPROBES=y
 CONFIG_KPROBES_ON_FTRACE=y
 CONFIG_UPROBES=y
+CONFIG_UPROBES_SUPPORT_PC_ALTER=y
 CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y
 CONFIG_ARCH_USE_BUILTIN_BSWAP=y
 CONFIG_KRETPROBES=y

include/linux/uprobes.h

@@ -22,8 +22,14 @@ struct inode;
 struct notifier_block;
 struct page;
 
-#define UPROBE_HANDLER_REMOVE		1
-#define UPROBE_HANDLER_MASK		1
+#define UPROBE_HANDLER_REMOVE          1
+
+#ifndef CONFIG_UPROBES_SUPPORT_PC_ALTER
+#define UPROBE_HANDLER_MASK            1
+#else
+#define UPROBE_ALTER_PC                0x2
+#define UPROBE_HANDLER_MASK            0x3
+#endif
 
 #define MAX_URETPROBE_DEPTH		64
 

kernel/events/uprobes.c

@@ -2070,10 +2070,17 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
 	return uprobe;
 }
 
+#ifdef CONFIG_UPROBES_SUPPORT_PC_ALTER
+static bool handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+#else
 static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+#endif
 {
 	struct uprobe_consumer *uc;
 	int remove = UPROBE_HANDLER_REMOVE;
+#ifdef CONFIG_UPROBES_SUPPORT_PC_ALTER
+	bool need_skip = false;
+#endif
 	bool need_prep = false; /* prepare return uprobe, when needed */
 
 	down_read(&uprobe->register_rwsem);
@@ -2090,6 +2097,10 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 			need_prep = true;
 
 		remove &= rc;
+#ifdef CONFIG_UPROBES_SUPPORT_PC_ALTER
+		if (rc & UPROBE_ALTER_PC)
+			need_skip = true;
+#endif
 	}
 
 	if (need_prep && !remove)
@@ -2100,6 +2111,9 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 		unapply_uprobe(uprobe, current->mm);
 	}
 	up_read(&uprobe->register_rwsem);
+#ifdef CONFIG_UPROBES_SUPPORT_PC_ALTER
+	return need_skip;
+#endif
 }
 
 static void
@@ -2241,7 +2255,12 @@ static void handle_swbp(struct pt_regs *regs)
 	if (arch_uprobe_ignore(&uprobe->arch, regs))
 		goto out;
 
+#ifdef CONFIG_UPROBES_SUPPORT_PC_ALTER
+	if (handler_chain(uprobe, regs))
+		goto out;
+#else
 	handler_chain(uprobe, regs);
+#endif
 
 	if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
 		goto out;