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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>

authored by

fuqiang wang and committed by
Andrew Morton d337f452 13f23538

+19 -4
+19 -4
arch/x86/kernel/crash.c
··· 165 165 /* 166 166 * Exclusion of crash region, crashk_low_res and/or crashk_cma_ranges 167 167 * may cause range splits. So add extra slots here. 168 + * 169 + * Exclusion of low 1M may not cause another range split, because the 170 + * range of exclude is [0, 1M] and the condition for splitting a new 171 + * region is that the start, end parameters are both in a certain 172 + * existing region in cmem and cannot be equal to existing region's 173 + * start or end. Obviously, the start of [0, 1M] cannot meet this 174 + * condition. 175 + * 176 + * But in order to lest the low 1M could be changed in the future, 177 + * (e.g. [start, 1M]), add a extra slot. 168 178 */ 169 - nr_ranges += 2 + crashk_cma_cnt; 179 + nr_ranges += 3 + crashk_cma_cnt; 170 180 cmem = vzalloc(struct_size(cmem, ranges, nr_ranges)); 171 181 if (!cmem) 172 182 return NULL; ··· 332 322 struct crash_mem *cmem; 333 323 334 324 /* 335 - * Using random kexec_buf for passing dm crypt keys may cause a range 336 - * split. So use two slots here. 325 + * In the current x86 architecture code, the elfheader is always 326 + * allocated at crashk_res.start. But it depends on the allocation 327 + * position of elfheader in crashk_res. To avoid potential out of 328 + * bounds in future, add an extra slot. 329 + * 330 + * And using random kexec_buf for passing dm crypt keys may cause a 331 + * range split too, add another extra slot here. 337 332 */ 338 - nr_ranges = 2; 333 + nr_ranges = 3; 339 334 cmem = vzalloc(struct_size(cmem, ranges, nr_ranges)); 340 335 if (!cmem) 341 336 return -ENOMEM;