Sashiko AI code review pointed out a there is a TOCTOU (Time-of-Check to
Time-of-Use) race condition in prepare_elf_headers() between the initial
pass that counts System RAM ranges and the second pass that populates them.
If a memory hotplug event occurs between these two steps, the number of
memory regions may increase, causing an out-of-bounds write to
the cmem->ranges[] array.

Directly introducing get_online_mems() inside prepare_elf_headers() would
trigger an immediate recursive read-after-write deadlock when invoked by
the runtime hotplug notification path (which already holds the hotplug
write lock).

To eliminate the TOCTOU window safely without deadlock risks, move the
get_online_mems() read lock to the top-level architecture image loaders.
Since these top-level loaders are strictly executed on the initial system
call path and are never re-entered by the runtime hotplug notifier, this
approach physically isolates the locking contexts. The system memory ranges
are forced to be statically frozen during the entire layout generation,
eradicating the buffer overflow vulnerability.

Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <redacted>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 8d5f894a3108 ("x86: kexec_file: lift CRASH_MAX_RANGES limit on crash_mem buffer")
Signed-off-by: Jinjie Ruan <redacted>
---
 arch/x86/kernel/crash.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index cd796818d94d..f319308b06ee 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c

@@ -25,6 +25,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/memblock.h>
+#include <linux/memory_hotplug.h>
 
 #include <asm/bootparam.h>
 #include <asm/processor.h>

@@ -226,6 +227,9 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 {
 	struct crash_mem *cmem = arg;
 
+	if (WARN_ON_ONCE(cmem->nr_ranges >= cmem->max_nr_ranges))
+		return -EAGAIN;
+
 	cmem->ranges[cmem->nr_ranges].start = res->start;
 	cmem->ranges[cmem->nr_ranges].end = res->end;
 	cmem->nr_ranges++;

@@ -419,10 +423,14 @@ int crash_load_segments(struct kimage *image)
 				  .buf_max = ULONG_MAX, .top_down = false };
 
 	/* Prepare elf headers and add a segment */
+	get_online_mems();
 	ret = prepare_elf_headers(&kbuf.buffer, &kbuf.bufsz, &pnum);
-	if (ret)
+	if (ret) {
+		put_online_mems();
 		return ret;
+	}
 
+	put_online_mems();
 	image->elf_headers	= kbuf.buffer;
 	image->elf_headers_sz	= kbuf.bufsz;
 	kbuf.memsz		= kbuf.bufsz;

-- 
2.34.1