[PATCH 14/23] tracing/kprobes: handle mixed kernel/userspace probes better

Christoph Hellwig
2020-05-21T15:23:52Z

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.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
kernel/trace/trace_kprobe.c | 72 ++++++++++++++++++++++---------------
1 file changed, 43 insertions(+), 29 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 4325f9e7fadaa..4aeaef53ba970 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1200,6 +1200,15 @@ 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_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)
@@ -1207,30 +1216,27 @@ 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);

@@ -1252,35 +1254,37 @@ 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_user_nofault(__dest, (void *)addr, maxlen);
if (ret >= 0)
*(u32 *)dest = make_data_loc(ret, __dest - base);

return ret;
}

-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)
{
@@ -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,
--
2.26.2