x86/kexec: fix potential cmem->ranges out of memory

In memmap_exclude_ranges(), elfheader will be excluded 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 new split range.  But it
depends on the allocation position of elfheader in crashk_res.  To avoid
potential out of memory in future, add a extra slot.  Otherwise loading
the kdump kernel will fail because crash_exclude_mem_range will return
-ENOMEM.  random kexec_buf for passing dm crypt keys may cause a range
split too, add another extra slot here.

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 cast the low 1M could be
changed in the future, add a extra slot too.

Previous discussions:
[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/

Link: https://lkml.kernel.org/r/20250904093855.1180154-1-coxu@redhat.com
Signed-off-by: fuqiang wang <fuqiang.wang@easystack.cn>
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: fuqiang wang

arch/x86/kernel/crash.c

@@ -165,8 +165,18 @@ static struct crash_mem *fill_up_crash_elf_data(void)
 	/*
 	 * Exclusion of crash region, crashk_low_res and/or crashk_cma_ranges
 	 * may cause range splits. So add extra 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. [start, 1M]), add a extra slot.
 	 */
-	nr_ranges += 2 + crashk_cma_cnt;
+	nr_ranges += 3 + crashk_cma_cnt;
 	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
 	if (!cmem)
 		return NULL;
@@ -322,10 +332,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 	struct crash_mem *cmem;
 
 	/*
-	 * Using random kexec_buf for passing dm crypt keys may cause a range
-	 * split. So use two slots here.
+	 * 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 an extra slot.
+	 *
+	 * And using random kexec_buf for passing dm crypt keys may cause a
+	 * range split too, add another extra slot here.
 	 */
-	nr_ranges = 2;
+	nr_ranges = 3;
 	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
 	if (!cmem)
 		return -ENOMEM;