tracing/kprobes: handle mixed kernel/userspace probes better

Instead of using the dangerous probe_kernel_read and strncpy_from_unsafe
helpers, rework probes to try a user probe based on the address if the
architecture has a common address space for kernel and userspace.

[svens@linux.ibm.com:use strncpy_from_kernel_nofault() in fetch_store_string()]
  Link: http://lkml.kernel.org/r/20200606181903.49384-1-svens@linux.ibm.com

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200521152301.2587579-15-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/trace/trace_kprobe.c

@@ -1200,21 +1200,6 @@ static const struct file_operations kprobe_profile_ops = {
 
 /* Kprobe specific fetch functions */
 
-/* Return the length of string -- including null terminal byte */
-static nokprobe_inline int
-fetch_store_strlen(unsigned long addr)
-{
-	int ret, len = 0;
-	u8 c;
-
-	do {
-		ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
-		len++;
-	} while (c && ret == 0 && len < MAX_STRING_SIZE);
-
-	return (ret < 0) ? ret : len;
-}
-
 /* Return the length of string -- including null terminal byte */
 static nokprobe_inline int
 fetch_store_strlen_user(unsigned long addr)
@@ -1224,31 +1209,24 @@ fetch_store_strlen_user(unsigned long addr)
 	return strnlen_user_nofault(uaddr, MAX_STRING_SIZE);
 }
 
-/*
- * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
- * length and relative data location.
- */
+/* Return the length of string -- including null terminal byte */
 static nokprobe_inline int
-fetch_store_string(unsigned long addr, void *dest, void *base)
+fetch_store_strlen(unsigned long addr)
 {
-	int maxlen = get_loc_len(*(u32 *)dest);
-	void *__dest;
-	long ret;
+	int ret, len = 0;
+	u8 c;
 
-	if (unlikely(!maxlen))
-		return -ENOMEM;
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+	if (addr < TASK_SIZE)
+		return fetch_store_strlen_user(addr);
+#endif
 
-	__dest = get_loc_data(dest, base);
+	do {
+		ret = probe_kernel_read_strict(&c, (u8 *)addr + len, 1);
+		len++;
+	} while (c && ret == 0 && len < MAX_STRING_SIZE);
 
-	/*
-	 * Try to get string again, since the string can be changed while
-	 * probing.
-	 */
-	ret = strncpy_from_unsafe(__dest, (void *)addr, maxlen);
-	if (ret >= 0)
-		*(u32 *)dest = make_data_loc(ret, __dest - base);
-
-	return ret;
+	return (ret < 0) ? ret : len;
 }
 
 /*
@@ -1275,10 +1253,36 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
 	return ret;
 }
 
+/*
+ * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
+ * length and relative data location.
+ */
 static nokprobe_inline int
-probe_mem_read(void *dest, void *src, size_t size)
+fetch_store_string(unsigned long addr, void *dest, void *base)
 {
-	return probe_kernel_read(dest, src, size);
+	int maxlen = get_loc_len(*(u32 *)dest);
+	void *__dest;
+	long ret;
+
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+	if ((unsigned long)addr < TASK_SIZE)
+		return fetch_store_string_user(addr, dest, base);
+#endif
+
+	if (unlikely(!maxlen))
+		return -ENOMEM;
+
+	__dest = get_loc_data(dest, base);
+
+	/*
+	 * Try to get string again, since the string can be changed while
+	 * probing.
+	 */
+	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
+	if (ret >= 0)
+		*(u32 *)dest = make_data_loc(ret, __dest - base);
+
+	return ret;
 }
 
 static nokprobe_inline int
@@ -1289,6 +1293,16 @@ probe_mem_read_user(void *dest, void *src, size_t size)
 	return probe_user_read(dest, uaddr, size);
 }
 
+static nokprobe_inline int
+probe_mem_read(void *dest, void *src, size_t size)
+{
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+	if ((unsigned long)src < TASK_SIZE)
+		return probe_mem_read_user(dest, src, size);
+#endif
+	return probe_kernel_read_strict(dest, src, size);
+}
+
 /* Note that we don't verify it, since the code does not come from user space */
 static int
 process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,