Re: [2/6] uaccess: add probe_kernel_write()

[Jan Kiszka]

Ingo Molnar wrote:
> From: Ingo Molnar <mingo@xxxxxxx>
> 
> add probe_kernel_write() - copy & paste of the existing
> probe_kernel_access(), extended to writes.

Along Linus' suggestion to work on larger chunks in kgdb, here are
improved probe_kernel_read/write helpers that take a size argument.

I'm leaving the original probe_kernel_read as is for now, but maybe it
can be converted to probe_kernel_read (I don't want to dive into this as
well :) ).

Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxx>

---
 uaccess.h |   38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 98cfe02..ef75869 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -85,25 +85,49 @@ static inline unsigned long __copy_from_user_nocache(void *to,
 	})
 
 /**
+ * probe_kernel_read(): safely attempt to read from a location
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from
+ * @size: size of the data chunk
+ *
+ * Safely read from address @src to the buffer at @dst.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+#define probe_kernel_read(dst, src, size)		\
+	({						\
+		long ret;				\
+		mm_segment_t old_fs = get_fs();		\
+							\
+		set_fs(KERNEL_DS);			\
+		pagefault_disable();			\
+		ret = __copy_from_user_inatomic((dst),	\
+	 (__force const void __user *)(src), (size));	\
+		pagefault_enable();			\
+		set_fs(old_fs);				\
+		ret ? -EFAULT : 0;			\
+	})
+
+/**
  * probe_kernel_write(): safely attempt to write to a location
- * @addr: address to write to - its type is type typeof(rdval)*
- * @rdval: write to this variable
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
  *
- * Safely write to address @addr from variable @rdval.  If a kernel fault
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
  * happens, handle that and return -EFAULT.
  */
-#define probe_kernel_write(addr, rdval)			\
+#define probe_kernel_write(dst, src, size)		\
 	({						\
 		long ret;				\
 		mm_segment_t old_fs = get_fs();		\
 							\
 		set_fs(KERNEL_DS);			\
 		pagefault_disable();			\
-		ret = __put_user(rdval,			\
-	 (__force typeof(rdval) __user *)(addr));	\
+		ret = __copy_to_user_inatomic(		\
+	 (__force void __user *)(dst), (src), (size));	\
 		pagefault_enable();			\
 		set_fs(old_fs);				\
-		ret;					\
+		ret ? -EFAULT : 0;			\
 	})
 
 #endif		/* __LINUX_UACCESS_H__ */
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