+ kexec-copy-only-happens-before-uchunk-goes-to-zero.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kexec: copy only happens before uchunk goes to zero
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kexec-copy-only-happens-before-uchunk-goes-to-zero.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kexec-copy-only-happens-before-uchunk-goes-to-zero.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "yang.zhang" <yang.zhang@hexintek.com>
Subject: kexec: copy only happens before uchunk goes to zero
Date: Thu, 22 Feb 2024 17:21:19 +0800

When loading segments, ubytes is <= mbytes.  When ubytes is exhausted,
there could be remaining mbytes.  Then in the while loop, the buf pointer
advancing with mchunk will causing meaningless reading even though it
doesn't harm.

So let's change to make sure that all of the copying and the rest only
happens before uchunk goes to zero.

Link: https://lkml.kernel.org/r/20240222092119.5602-1-gaoshanliukou@163.com
Signed-off-by: yang.zhang <yang.zhang@hexintek.com>
Acked-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/kexec_core.c |   44 ++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

--- a/kernel/kexec_core.c~kexec-copy-only-happens-before-uchunk-goes-to-zero
+++ a/kernel/kexec_core.c
@@ -750,22 +750,24 @@ static int kimage_load_normal_segment(st
 				PAGE_SIZE - (maddr & ~PAGE_MASK));
 		uchunk = min(ubytes, mchunk);
 
-		/* For file based kexec, source pages are in kernel memory */
-		if (image->file_mode)
-			memcpy(ptr, kbuf, uchunk);
-		else
-			result = copy_from_user(ptr, buf, uchunk);
+		if (uchunk) {
+			/* For file based kexec, source pages are in kernel memory */
+			if (image->file_mode)
+				memcpy(ptr, kbuf, uchunk);
+			else
+				result = copy_from_user(ptr, buf, uchunk);
+			ubytes -= uchunk;
+			if (image->file_mode)
+				kbuf += uchunk;
+			else
+				buf += uchunk;
+		}
 		kunmap_local(ptr);
 		if (result) {
 			result = -EFAULT;
 			goto out;
 		}
-		ubytes -= uchunk;
 		maddr  += mchunk;
-		if (image->file_mode)
-			kbuf += mchunk;
-		else
-			buf += mchunk;
 		mbytes -= mchunk;
 
 		cond_resched();
@@ -817,11 +819,18 @@ static int kimage_load_crash_segment(str
 			memset(ptr + uchunk, 0, mchunk - uchunk);
 		}
 
-		/* For file based kexec, source pages are in kernel memory */
-		if (image->file_mode)
-			memcpy(ptr, kbuf, uchunk);
-		else
-			result = copy_from_user(ptr, buf, uchunk);
+		if (uchunk) {
+			/* For file based kexec, source pages are in kernel memory */
+			if (image->file_mode)
+				memcpy(ptr, kbuf, uchunk);
+			else
+				result = copy_from_user(ptr, buf, uchunk);
+			ubytes -= uchunk;
+			if (image->file_mode)
+				kbuf += uchunk;
+			else
+				buf += uchunk;
+		}
 		kexec_flush_icache_page(page);
 		kunmap_local(ptr);
 		arch_kexec_pre_free_pages(page_address(page), 1);
@@ -829,12 +838,7 @@ static int kimage_load_crash_segment(str
 			result = -EFAULT;
 			goto out;
 		}
-		ubytes -= uchunk;
 		maddr  += mchunk;
-		if (image->file_mode)
-			kbuf += mchunk;
-		else
-			buf += mchunk;
 		mbytes -= mchunk;
 
 		cond_resched();
_

Patches currently in -mm which might be from yang.zhang@hexintek.com are

kexec-copy-only-happens-before-uchunk-goes-to-zero.patch