uaccess: add probe_kernel_write()

add probe_kernel_read() and probe_kernel_write().

Uninlined and restricted to kernel range memory only, as suggested
by Linus.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 975c963e57898aee95fed95e129bd91a1578a414..fec6decfb983503ec8ae24bafa793f09b5f902b2 100644 (file)
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -84,4 +84,26 @@ static inline unsigned long __copy_from_user_nocache(void *to,
                ret;                                    \
        })
 
+/*
+ * 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.
+ */
+extern long probe_kernel_read(void *dst, void *src, size_t size);
+
+/*
+ * probe_kernel_write(): safely attempt to write to a location
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
+ *
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+extern long probe_kernel_write(void *dst, void *src, size_t size);
+
 #endif         /* __LINUX_UACCESS_H__ */

diff --git a/mm/Makefile b/mm/Makefile
index a5b0dd93427a7266d7a26dcc7fd1266c602725fb..18c143b3c46cd599c0822f64f503e134361b0aac 100644 (file)
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -8,7 +8,7 @@ mmu-$(CONFIG_MMU)       := fremap.o highmem.o madvise.o memory.o mincore.o \
                           vmalloc.o
 
 obj-y                  := bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
-                          page_alloc.o page-writeback.o pdflush.o \
+                          maccess.o page_alloc.o page-writeback.o pdflush.o \
                           readahead.o swap.o truncate.o vmscan.o \
                           prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
                           page_isolation.o $(mmu-y)

diff --git a/mm/maccess.c b/mm/maccess.c
new file mode 100644 (file)
index 0000000..24f81b9
--- /dev/null
+++ b/mm/maccess.c
@@ -0,0 +1,49 @@
+/*
+ * Access kernel memory without faulting.
+ */
+#include <linux/uaccess.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+
+/**
+ * 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.
+ */
+long probe_kernel_read(void *dst, void *src, size_t size)
+{
+       long ret;
+
+       pagefault_disable();
+       ret = __copy_from_user_inatomic(dst,
+                       (__force const void __user *)src, size);
+       pagefault_enable();
+
+       return ret ? -EFAULT : 0;
+}
+EXPORT_SYMBOL_GPL(probe_kernel_read);
+
+/**
+ * probe_kernel_write(): safely attempt to write to a location
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
+ *
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+long probe_kernel_write(void *dst, void *src, size_t size)
+{
+       long ret;
+
+       pagefault_disable();
+       ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
+       pagefault_enable();
+
+       return ret ? -EFAULT : 0;
+}
+EXPORT_SYMBOL_GPL(probe_kernel_write);