FAILED: patch "[PATCH] powerpc/kexec_file: Prevent kexec range truncation" failed to apply to 6.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x fa40f9dbdd4af53e7445d9135b5b207eb8adf372
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090924-deskwork-unvocal-d17e@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fa40f9dbdd4af53e7445d9135b5b207eb8adf372 Mon Sep 17 00:00:00 2001
From: Jinjie Ruan <ruanjinjie@huawei.com>
Date: Wed, 29 Jul 2026 09:29:48 +0800
Subject: [PATCH] powerpc/kexec_file: Prevent kexec range truncation

Sashiko AI review pointed out the following issue.

The __merge_memory_ranges() function incorrectly handles overlapping
memory ranges when merging them. Although sort_memory_ranges() sorts all
ranges by their start address in ascending order beforehand, the merge
logic remains defective in two ways:

1. It compares the current range's start against the previous element (i-1)
   instead of the running target index (idx)

2. It unconditionally overwrites 'ranges[idx].end' with 'ranges[i].end'.

This logic flaw leads to critical memory truncation when a larger memory
range completely subsumes subsequent smaller ranges.

For example, consider a sorted input array with three ranges:
  Range A (idx=0): [0x1000 - 0x9000]
  Range B (i=1):   [0x2000 - 0x5000] (completely inside Range A)
  Range C (i=2):   [0x6000 - 0x8000] (completely inside Range A)

1. When i=1 (Range B):
   ranges[1].start (0x2000) <= ranges[0].end + 1 (0x9001) is TRUE.
   The code executes: ranges[0].end = ranges[1].end, which erroneously
   shrinks Range A's end from 0x9000 down to 0x5000.

2. When i=2 (Range C):
   ranges[2].start (0x6000) <= ranges[1].end + 1 (0x5001) is FALSE.
   The code falls into the else block, creating a broken new range.

As a result, valid memory fragments [0x5001 - 0x5fff] and [0x8001 - 0x9000]
are completely lost from the kexec exclude lists, potentially allowing
the crash kernel to overwrite active memory, causing data corruption
or crashes.

Fix this by ensuring the start of the current range is compared against the
end of the active merged range (idx), and use max() to safely prevent the
outer boundary from being truncated.

Cc: stable@vger.kernel.org
Fixes: 180adfc532a8 ("powerpc/kexec_file: Add helper functions for getting memory ranges")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260729012948.2797865-4-ruanjinjie@huawei.com

diff --git a/arch/powerpc/kexec/ranges.c b/arch/powerpc/kexec/ranges.c
index 867135560e5c..eb45e89502ca 100644
--- a/arch/powerpc/kexec/ranges.c
+++ b/arch/powerpc/kexec/ranges.c
@@ -21,6 +21,7 @@
 #include <linux/of.h>
 #include <linux/slab.h>
 #include <linux/memblock.h>
+#include <linux/minmax.h>
 #include <linux/crash_core.h>
 #include <asm/sections.h>
 #include <asm/kexec_ranges.h>
@@ -105,19 +106,16 @@ static void __merge_memory_ranges(struct crash_mem *mem_rngs)
 	struct range *ranges;
 	int i, idx;
 
-	if (!mem_rngs)
+	if (!mem_rngs || mem_rngs->nr_ranges <= 1)
 		return;
 
 	idx = 0;
-	ranges = &(mem_rngs->ranges[0]);
+	ranges = mem_rngs->ranges;
 	for (i = 1; i < mem_rngs->nr_ranges; i++) {
-		if (ranges[i].start <= (ranges[i-1].end + 1))
-			ranges[idx].end = ranges[i].end;
+		if (ranges[i].start <= (ranges[idx].end + 1))
+			ranges[idx].end = max(ranges[idx].end, ranges[i].end);
 		else {
 			idx++;
-			if (i == idx)
-				continue;
-
 			ranges[idx] = ranges[i];
 		}
 	}