[PATCH v3] x86/kexec: fix potential cmem->ranges out of bounds

[fuqiang wang <fuqiang.wang@easystack.cn>]

In memmap_exclude_ranges(), there will exclude elfheader from
crashk_res. In the current x86 architecture code, the elfheader is
always allocated at crashk_res.start. It seems that there won't be a
split a new range. But it depends on the allocation position of
elfheader in crashk_res. To avoid potential out of bounds in future, add
a extra slot.

The similar issue also exists in fill_up_crash_elf_data(). The range to
be excluded is [0, 1M], start (0) is special and will not appear in the
middle of existing cmem->ranges[]. But in order to lest the low 1M could
be changed in the future, add a extra slot too.

Previously discussed link:
[1] https://lore.kernel.org/kexec/ZXk2oBf%2FT1Ul6o0c@MiWiFi-R3L-srv/
[2] https://lore.kernel.org/kexec/273284e8-7680-4f5f-8065-c5d780987e59@easystack.cn/
[3] https://lore.kernel.org/kexec/ZYQ6O%2F57sHAPxTHm@MiWiFi-R3L-srv/

Signed-off-by: fuqiang wang <fuqiang.wang@easystack.cn>
---
 arch/x86/kernel/crash.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..97d33a6fc4fb 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -149,8 +149,18 @@ static struct crash_mem *fill_up_crash_elf_data(void)
 	/*
 	 * Exclusion of crash region and/or crashk_low_res may cause
 	 * another range split. So add extra two slots here.
+	 *
+	 * Exclusion of low 1M may not cause another range split, because the
+	 * range of exclude is [0, 1M] and the condition for splitting a new
+	 * region is that the start, end parameters are both in a certain
+	 * existing region in cmem and cannot be equal to existing region's
+	 * start or end. Obviously, the start of [0, 1M] cannot meet this
+	 * condition.
+	 *
+	 * But in order to lest the low 1M could be changed in the future,
+	 * (e.g. [stare, 1M]), add a extra slot.
 	 */
-	nr_ranges += 2;
+	nr_ranges += 3;
 	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
 	if (!cmem)
 		return NULL;
@@ -282,9 +292,16 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 	struct crash_memmap_data cmd;
 	struct crash_mem *cmem;
 
-	cmem = vzalloc(struct_size(cmem, ranges, 1));
+	/*
+	 * In the current x86 architecture code, the elfheader is always
+	 * allocated at crashk_res.start. But it depends on the allocation
+	 * position of elfheader in crashk_res. To avoid potential out of
+	 * bounds in future, add a extra slot.
+	 */
+	cmem = vzalloc(struct_size(cmem, ranges, 2));
 	if (!cmem)
 		return -ENOMEM;
+	cmem->max_nr_ranges = 2;
 
 	memset(&cmd, 0, sizeof(struct crash_memmap_data));
 	cmd.params = params;
-- 
2.42.0