From: Kairui Song <kasong@xxxxxxxxxxx>
Since kernel commit 14c127c957c1 ('arm64: mm: Flip kernel VA space'),
the memory layout on arm64 have changed, and kexec-tools can no longer
get the the right PAGE_OFFSET based on _text symbol.
Prior to that, the kimage (_text) lays above PAGE_END with this layout:
0 -> VA_START : Usespace
VA_START -> VA_START + 256M : BPF JIT, Modules
VA_START + 256M -> PAGE_OFFSET - (~GB misc) : Vmalloc (KERNEL _text HERE)
PAGE_OFFSET -> ... : * Linear map *
And here we have:
VA_START = -1UL << VA_BITS
PAGE_OFFSET = -1UL << (VA_BITS - 1)
_text < -1UL << (VA_BITS - 1)
Kernel image lays somewhere between VA_START and PAGE_OFFSET, so we just
calc VA_BITS by getting the highest unset bit of _text symbol address,
and shift one less bit of VA_BITS to get page offset. This works as long
as KASLR don't put kernel in a too high location (which is commented inline).
And after that commit, kernel layout have changed:
0 -> PAGE_OFFSET : Userspace
PAGE_OFFSET -> PAGE_END : * Linear map *
PAGE_END -> PAGE_END + 128M : bpf jit region
PAGE_END + 128M -> PAGE_END + 256MB : modules
PAGE_END + 256M -> ... : vmalloc (KERNEL _text HERE)
Here we have:
PAGE_OFFSET = -1UL << VA_BITS
PAGE_END = -1UL << (VA_BITS - 1)
_text > -1UL << (VA_BITS - 1)
Kernel image now lays above PAGE_END, so we have to shift one more bit to
get the VA_BITS, and shift the exact VA_BITS for PAGE_OFFSET.
We can simply check if "_text > -1UL << (VA_BITS - 1)" is true to judge
which layout is being used and shift the page offset occordingly.
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
(rebased and stripped by Pingfan )
Signed-off-by: Pingfan Liu <piliu@xxxxxxxxxx>
Cc: Simon Horman <horms@xxxxxxxxxxxx>
Cc: Philipp Rudo <prudo@xxxxxxxxxx>
To: kexec@xxxxxxxxxxxxxxxxxxx
---
kexec/arch/arm64/kexec-arm64.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
index 793799b..ce7a5bb 100644
--- a/kexec/arch/arm64/kexec-arm64.c
+++ b/kexec/arch/arm64/kexec-arm64.c
@@ -923,13 +923,25 @@ out:
int get_page_offset(unsigned long *page_offset)
{
+ unsigned long long text_sym_addr, kernel_va_mid;
int ret;
+ text_sym_addr = get_kernel_sym("_text");
+ if (text_sym_addr == 0) {
+ fprintf(stderr, "Can't get the symbol of _text to calculate page_offset.\n");
+ return -1;
+ }
+
ret = get_va_bits();
if (ret < 0)
return ret;
- if (va_bits < 52)
+ /* Since kernel 5.4, kernel image is put above
+ * UINT64_MAX << (va_bits - 1)
+ */
+ kernel_va_mid = UINT64_MAX << (va_bits - 1);
+ /* older kernel */
+ if (text_sym_addr < kernel_va_mid)
*page_offset = UINT64_MAX << (va_bits - 1);
else
*page_offset = UINT64_MAX << va_bits;
--
2.31.1
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