linux-kernel - [RFC PATCH 03/14] fs/proc/vmcore: Update copy_oldmem

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Message-Id: <20211203104231.17597-4-amit.kachhap@arm.com>
Date:   Fri,  3 Dec 2021 16:12:20 +0530
From:   Amit Daniel Kachhap <amit.kachhap@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Christoph Hellwig <hch@....de>,
        Vincenzo Frascino <Vincenzo.Frascino@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        kexec <kexec@...ts.infradead.org>,
        Amit Daniel Kachhap <amit.kachhap@....com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>
Subject: [RFC PATCH 03/14] fs/proc/vmcore: Update copy_oldmem_page() for user buffer

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@...hat.com>
Cc: Baoquan He <bhe@...hat.com>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: kexec <kexec@...ts.infradead.org>
Cc: linux-fsdevel <linux-fsdevel@...r.kernel.org>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
---
 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