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>

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 4325f9e..6a23b45 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1202,35 +1202,41 @@ static const struct file_operations kprobe_profile_ops = {
 
 /* Return the length of string -- including null terminal byte */
 static nokprobe_inline int
+fetch_store_strlen_user(unsigned long addr)
+{
+       const void __user *uaddr =  (__force const void __user *)addr;
+
+       return strnlen_user_nofault(uaddr, MAX_STRING_SIZE);
+}
+
+/* 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;
 
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+       if (addr < TASK_SIZE)
+               return fetch_store_strlen_user(addr);
+#endif
+
        do {
-               ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
+               ret = probe_kernel_read_strict(&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)
-{
-       const void __user *uaddr =  (__force const void __user *)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.
+ * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
+ * with max length and relative data location.
  */
 static nokprobe_inline int
-fetch_store_string(unsigned long addr, void *dest, void *base)
+fetch_store_string_user(unsigned long addr, void *dest, void *base)
 {
+       const void __user *uaddr =  (__force const void __user *)addr;
        int maxlen = get_loc_len(*(u32 *)dest);
        void *__dest;
        long ret;
@@ -1240,11 +1246,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 
        __dest = get_loc_data(dest, base);
 
-       /*
-        * Try to get string again, since the string can be changed while
-        * probing.
-        */
-       ret = strncpy_from_unsafe(__dest, (void *)addr, maxlen);
+       ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
        if (ret >= 0)
                *(u32 *)dest = make_data_loc(ret, __dest - base);
 
@@ -1252,23 +1254,31 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 }
 
 /*
- * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
- * with max length and relative data location.
+ * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
+ * length and relative data location.
  */
 static nokprobe_inline int
-fetch_store_string_user(unsigned long addr, void *dest, void *base)
+fetch_store_string(unsigned long addr, void *dest, void *base)
 {
-       const void __user *uaddr =  (__force const void __user *)addr;
        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);
 
-       ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
+       /*
+        * 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);
 
@@ -1276,12 +1286,6 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
 }
 
 static nokprobe_inline int
-probe_mem_read(void *dest, void *src, size_t size)
-{
-       return probe_kernel_read(dest, src, size);
-}
-
-static nokprobe_inline int
 probe_mem_read_user(void *dest, void *src, size_t size)
 {
        const void __user *uaddr =  (__force const void __user *)src;
@@ -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,