** Information type changed from Public to Public Security
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https://bugs.launchpad.net/bugs/1916076
Title:
Support kernel 4.15 in Trusty kexec-tools
Status in kexec-tools package in Ubuntu:
In Progress
Status in kexec-tools source package in Trusty:
In Progress
Bug description:
[Impact]
* In Trusty/Azure we have a kernel 4.15 package - this kernel has a bunch of
improvements compared to Trusty HWE, including KASLR. That reflects a lot in
the memory topology/mapping, which affects the kexec procedure.
- In order to support kexec operation for kdump in Trusty/Azure running
kernel 4.15, the following patches are needed, and hereby backported:
0d526445 ("x86, kaslr: add alternative way to locate kernel text mapping
area")
9f62cbdd ("kexec/arch/i386: Add support for KASLR memory randomization")
dbb99d93 ("kexec-tools/x86: get_kernel_vaddr_and_size off-by-one fix")
ed15ba1b ("build_mem_phdrs(): check if p_paddr is invalid")
fab91841 ("Handle additional e820 memmap type strings")
- All the above patches are included in kexec-tools from Xenial, so
they are exercised by Xenial's users for the last years.
[Test Case]
* To test and exhibit the issue, just execute both "kexec -l" (regular load)
and "kexec -p" (kdump kernel load) operations in an Azure instance running
Trusty with the latest trusty-updates version of the package (2.0.6-0ubuntu2.3)
- it will fail.
* Using the patches hereby backported, both operations succeed and
kdump kernel is initialized when an artificial panic is triggered
using "echo c > /proc/sysrq"
[Where problems could occur]
* As previously mentioned, all the patches are present in Xenial and
subsequent versions of kexec-tools; since all of them are not invasive and
kexec-tools is backward compatible, the potential for regressions is pretty low.
* That said, if we face problems due to the patches proposed here, the
issues would show-up during kdump/regular kexec load operations.
* Worth to mention that in kernel 4.4, the following message is
observed when loading a kdump kernel after the patches: "Cannot get
kernel page_offset_base symbol address". This is expected, since kexec
will try new methods to get memory information (which will succeed in
more recent kernels), but will fallback to the old methods in old
kernels, showing this message.
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