[RFC PATCH 03/14] fs/proc/vmcore: Update copy_oldmem_page() for user buffer

[Amit Daniel Kachhap]

The exported interface copy_oldmem_page passes user pointer without
__user annotation and does unnecessary user/kernel pointer
conversions during the pointer propagation.

Hence it is modified to have a new parameter for user pointer. However
instead of updating it directly a new interface copy_oldmem_page_buf()
is added as copy_oldmem_page() is used across different archs. This old
interface copy_oldmem_page() will be deleted after all the archs are
modified to use the new interface.

The weak implementation of both copy_oldmem_page() and
copy_oldmem_page_buf() are added temporarily to keep the kernel building
for the subsequent patches. As a consequence, crash dump is temporarily
broken for the archs till the patch where it implements its own
copy_oldmem_page_buf().

Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: kexec <kexec@xxxxxxxxxxxxxxxxxxx>
Cc: linux-fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
---
 fs/proc/vmcore.c           | 27 +++++++++++++++++----------
 include/linux/crash_dump.h |  3 +++
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index fa4492ef6124..d01b85c043dd 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -172,12 +172,9 @@ ssize_t read_from_oldmem(char __user *ubuf, char *kbuf, size_t count,
 				tmp = copy_oldmem_page_encrypted(pfn, ubuf,
 								 kbuf, nr_bytes,
 								 offset);
-			else if (ubuf)
-				tmp = copy_oldmem_page(pfn, (__force char *)ubuf,
-						       nr_bytes, offset, 1);
 			else
-				tmp = copy_oldmem_page(pfn, kbuf, nr_bytes,
-						       offset, 0);
+				tmp = copy_oldmem_page_buf(pfn, ubuf, kbuf,
+							   nr_bytes, offset);
 		}
 		if (tmp < 0) {
 			up_read(&vmcore_cb_rwsem);
@@ -244,11 +241,21 @@ ssize_t __weak
 copy_oldmem_page_encrypted(unsigned long pfn, char __user *ubuf, char *kbuf,
 			   size_t csize, unsigned long offset)
 {
-	if (ubuf)
-		return copy_oldmem_page(pfn, (__force char *)ubuf, csize,
-					offset, 1);
-	else
-		return copy_oldmem_page(pfn, kbuf, csize, offset, 0);
+	return copy_oldmem_page_buf(pfn, ubuf, kbuf, csize, offset);
+}
+
+ssize_t __weak
+copy_oldmem_page_buf(unsigned long pfn, char __user *ubuf, char *kbuf,
+		     size_t csize, unsigned long offset)
+{
+	return -EOPNOTSUPP;
+}
+
+ssize_t __weak
+copy_oldmem_page(unsigned long pfn, char *ubuf, size_t csize,
+		 unsigned long offset, int userbuf)
+{
+	return -EOPNOTSUPP;
 }
 
 /*
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 36a7f08f4ad2..725c4e053ecf 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -26,6 +26,9 @@ extern int remap_oldmem_pfn_range(struct vm_area_struct *vma,
 
 extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
 						unsigned long, int);
+extern ssize_t copy_oldmem_page_buf(unsigned long pfn, char __user *ubuf,
+				    char *kbuf, size_t csize,
+				    unsigned long offset);
 extern ssize_t copy_oldmem_page_encrypted(unsigned long pfn,
 					  char __user *ubuf, char *kbuf,
 					  size_t csize, unsigned long offset);
-- 
2.17.1