[PATCH v5] x86/kexec: fix potential cmem->ranges out of bounds

[Baoquan He <bhe@redhat.com>]

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 bounds in future, add a extra slot. And using
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@easystack.cn>
Signed-off-by: Baoquan He <bhe@redhat.com>
---
v4->v5:
- 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 bcb534688dfe..749a60ce8b7f 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 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;
@@ -313,10 +323,15 @@ 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;
-- 
2.41.0