linux-kernel - [RFC PATCH 05/14] x86/crash_dump_32: Use the new interface copy_oldmem_page

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Message-Id: <20211203104231.17597-6-amit.kachhap@arm.com>
Date:   Fri,  3 Dec 2021 16:12:22 +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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86 <x86@...nel.org>
Subject: [RFC PATCH 05/14] x86/crash_dump_32: Use the new interface copy_oldmem_page_buf

The current interface copy_oldmem_page() passes user pointer without
__user annotation and hence does unnecessary user/kernel pointer
conversions during its implementation.

Implement the interface copy_oldmem_page_buf() to avoid this issue.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86 <x86@...nel.org>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
---
 arch/x86/kernel/crash_dump_32.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index 5fcac46aaf6b..9932cd62ded1 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -30,20 +30,20 @@ static inline bool is_crashed_pfn_valid(unsigned long pfn)
 }
 
 /**
- * copy_oldmem_page - copy one page from "oldmem"
+ * copy_oldmem_page_buf - copy one page from "oldmem"
  * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
+ * @ubuf: target user memory pointer for the copy; use copy_to_user() if this
+ * pointer is not NULL
+ * @kbuf: target kernel memory pointer for the copy; use memcpy() if this
+ * pointer is not NULL
  * @csize: number of bytes to copy
  * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
  *
- * Copy a page from "oldmem". For this page, there might be no pte mapped
- * in the current kernel.
+ * Copy a page from "oldmem" into the buffer pointed by either @ubuf or @kbuf.
+ * For this page, there might be no pte mapped in the current kernel.
  */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
-			 unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page_buf(unsigned long pfn, char __user *ubuf, char *kbuf,
+			     size_t csize, unsigned long offset)
 {
 	void  *vaddr;
 
@@ -55,10 +55,10 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
 
 	vaddr = kmap_local_pfn(pfn);
 
-	if (!userbuf) {
-		memcpy(buf, vaddr + offset, csize);
+	if (!ubuf) {
+		memcpy(kbuf, vaddr + offset, csize);
 	} else {
-		if (copy_to_user(buf, vaddr + offset, csize))
+		if (copy_to_user(ubuf, vaddr + offset, csize))
 			csize = -EFAULT;
 	}
 
-- 
2.17.1