[PATCH v6 1/2] x86/kexec: fix potential cmem->ranges out of memory

[Coiby Xu]

From: fuqiang wang <fuqiang.wang at easystack.cn>

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.

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 at easystack.cn>
Signed-off-by: Baoquan He <bhe at redhat.com>
Signed-off-by: Coiby Xu <coxu at redhat.com>
---
v5->v6:
- rebase onto v6.17-rc4

v4->v5 (Baoquan):
- This is on top of Coiby's LUKS patchset in branch mm-nonmm-unstable of
  akpm/mm.git. I did some adaption based on Coiby's patches.
- [PATCH v9 0/8] Support kdump with LUKS encryption by reusing LUKS volume keys

 arch/x86/kernel/crash.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c6b12bed173d..5efdcd95a283 100644
--- a/arch/x86/kernel/crash.c
+++ b/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;
@@ -323,10 +333,15 @@ 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;

base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
-- 
2.51.0