[PATCH v14 07/17] riscv: kexec_file: Fix potential buffer overflow in prepare_elf_headers()

[Jinjie Ruan]

Sashiko AI code review pointed out 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: Paul Walmsley <pjw at kernel.org>
Cc: Palmer Dabbelt <palmer at dabbelt.com>
Cc: Albert Ou <aou at eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex at ghiti.fr>
Cc: songshuaishuai at tinylab.org
Cc: bjorn at rivosinc.com
Cc: leitao at debian.org
Fixes: 8acea455fafa ("RISC-V: Support for kexec_file on panic")
Reviewed-by: Guo Ren <guoren at kernel.org>
Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 arch/riscv/kernel/machine_kexec_file.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/kernel/machine_kexec_file.c b/arch/riscv/kernel/machine_kexec_file.c
index 3f7766057cac..a88362dfbd89 100644
--- a/arch/riscv/kernel/machine_kexec_file.c
+++ b/arch/riscv/kernel/machine_kexec_file.c
@@ -8,6 +8,7 @@
  */
 #include <linux/kexec.h>
 #include <linux/elf.h>
+#include <linux/memory_hotplug.h>
 #include <linux/slab.h>
 #include <linux/of.h>
 #include <linux/libfdt.h>
@@ -48,6 +49,9 @@ 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++;
@@ -281,12 +285,15 @@ int load_extra_segments(struct kimage *image, unsigned long kernel_start,
 	if (image->type == KEXEC_TYPE_CRASH) {
 		void *headers;
 		unsigned long headers_sz;
+		get_online_mems();
 		ret = prepare_elf_headers(&headers, &headers_sz);
 		if (ret) {
+			put_online_mems();
 			pr_err("Preparing elf core header failed\n");
 			goto out;
 		}
 
+		put_online_mems();
 		kbuf.buffer = headers;
 		kbuf.bufsz = headers_sz;
 		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
-- 
2.34.1