[PATCH 0/4 v8] Support kdump for AMD secure memory encryption(SME)

[Lianbo Jiang]

When SME is enabled on AMD machine, it also needs to support kdump. Because
the memory is encrypted in the first kernel, the old memory will be remapped
to kdump kernel for dumping data, and SME is also enabled in kdump kernel,
otherwise the old memory can not be decrypted.

For the kdump, it is necessary to distinguish whether the memory is encrypted.
Furthermore, that should also know which part of the memory is encrypted or
decrypted. It will appropriately remap the memory according to the specific
situation in order to tell cpu how to access the memory.

As we know, a page of memory that is marked as encrypted, which will be
automatically decrypted when read from DRAM, and will also be automatically
encrypted when written to DRAM. If the old memory is encrypted, it has to
remap the old memory with the memory encryption mask, which will automatically
decrypt the old memory when read from DRAM.

For kdump(SME), there are two cases that doesn't support:

 ----------------------------------------------
| first-kernel | second-kernel | kdump support |
|      (mem_encrypt=on|off)    |   (yes|no)    |
|--------------+---------------+---------------|
|     on       |     on        |     yes       |
|     off      |     off       |     yes       |
|     on       |     off       |     no        |
|     off      |     on        |     no        |
|______________|_______________|_______________|

1. SME is enabled in the first kernel, but SME is disabled in kdump kernel
In this case, because the old memory is encrypted, it can't be decrypted.
The root cause is that the encryption key is not visible to any software
runnint on the CPU cores(AMD cpu with SME), and is randomly generated on
eache system reset. That is to say, kdump kernel won't have a chance to
get the encryption key. So the encrypted memory can not be decrypted
unless SME is active.

2. SME is disabled in the first kernel, but SME is enabled in kdump kernel
It is unnecessary to support in this case, because the old memory is
dencrypted, the old memory can be dumped as usual, that doesn't need to
enable SME in kdump kernel. Another, If the scenario must be supported, it
will increase the complexity of the code, that will have to consider how to
pass the SME flag from the first kernel to the kdump kernel, in order to let
kdump kernel know that whether the old memory is encrypted.

There are two methods to pass the SME flag to the kdump kernel. The first
method is to modify the assembly code, which includes some common code and
the path is too long. The second method is to use kexec tool, which could
require the SME flag to be exported in the first kernel by "proc" or "sysfs",
kexec tools will read the SME flag from "proc" or "sysfs" when we use kexec
tools to load image, subsequently the SME flag will be saved in boot_params,
that can properly remap the old memory according to the previously saved SME
flag. But it is too expensive to do this.

This patches are only for SME kdump, the patches don't support SEV kdump.

Test tools:
makedumpfile[v1.6.3]: https://github.com/LianboJ/makedumpfile
commit <e1de103eca8f> "A draft for kdump vmcore about AMD SME"
Note: This patch can only dump vmcore in the case of SME enabled.

crash-7.2.3: https://github.com/crash-utility/crash.git
commit <001f77a05585> "Fix for Linux 4.19-rc1 and later kernels that contain kernel commit <7290d5809571>"

kexec-tools-2.0.17: git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
commit <b9de21ef51a7> "kexec: fix for "Unhandled rela relocation: R_X86_64_PLT32" error"

Note:
Before you load the kernel and initramfs for kdump, this patch(
http://lists.infradead.org/pipermail/kexec/2018-September/021460.html) must be merged
to kexec-tools, and then the kdump kernel will work well. Because there is a patch
which is removed based on v6(x86/ioremap: strengthen the logic in
early_memremap_pgprot_adjust() to adjust encryption mask).

Test environment:
HP ProLiant DL385Gen10 AMD EPYC 7251
8-Core Processor
32768 MB memory
600 GB disk space

Linux 4.19-rc5:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
commit <6bf4ca7fbc85> "Linux 4.19-rc5"

Reference:
AMD64 Architecture Programmer's Manual
https://support.amd.com/TechDocs/24593.pdf

Changes since v6:
1. There is a patch which is removed based on v6.
(x86/ioremap: strengthen the logic in early_memremap_pgprot_adjust() to adjust encryption mask)
Dave Young suggests that this patch can be removed and fix the kexec-tools.
Reference: http://lists.infradead.org/pipermail/kexec/2018-September/021460.html)
2. Update the patch log.

Changes since v7:
1. Improve patch log for patch 1/4(Suggested by Baoquan He)
2. Add Reviewed-by for all patches(Tom Lendacky <thomas.lendacky@xxxxxxx>)
3. Add Acked-by for patch 3/4(Joerg Roedel <jroedel@xxxxxxx>)
4. Remove header file(linux/crash_dump.h) from
arch/x86/mm/ioremap.c(Suggested by Borislav)
5. Modify comment and patch log for patch 2/4(Suggested by Borislav)
6. Delete a file arch/x86/kernel/crash_dump_encrypt.c and rewrite some
functions(Suggested by Borislav)
7. Modify all code style issue(Suggested by Borislav)

Some known issues:
1. about SME
Upstream kernel will hang on HP machine(DL385Gen10 AMD EPYC 7251) when
we execute the kexec command as follow:

# kexec -l /boot/vmlinuz-4.19.0-rc5+ --initrd=/boot/initramfs-4.19.0-rc5+.img --command-line="root=/dev/mapper/rhel_hp--dl385g10--03-root ro mem_encrypt=on rd.lvm.lv=rhel_hp-dl385g10-03/root rd.lvm.lv=rhel_hp-dl385g10-03/swap console=ttyS0,115200n81 LANG=en_US.UTF-8 earlyprintk=serial debug nokaslr"
# kexec -e (or reboot)

But this issue can not be reproduced on speedway machine, and this issue
is irrelevant to my posted patches.

The kernel log:
[ 1248.932239] kexec_core: Starting new kernel
early console in extract_kernel
input_data: 0x000000087e91c3b4
input_len: 0x000000000067fcbd
output: 0x000000087d400000
output_len: 0x0000000001b6fa90
kernel_total_size: 0x0000000001a9d000
trampoline_32bit: 0x0000000000099000

Decompressing Linux...
Parsing ELF...        [---Here the system will hang]

Lianbo Jiang (4):
  x86/ioremap: add a function ioremap_encrypted() to remap kdump old
    memory
  kexec: allocate decrypted control pages for kdump in case SME is
    enabled
  iommu/amd: Remap the device table of IOMMU with the memory encryption
    mask for kdump
  kdump/vmcore: support encrypted old memory with SME enabled

 arch/x86/include/asm/io.h       |  2 +
 arch/x86/kernel/crash_dump_64.c | 65 ++++++++++++++++++++++++++++-----
 arch/x86/mm/ioremap.c           | 24 ++++++++----
 drivers/iommu/amd_iommu_init.c  | 14 ++++++-
 fs/proc/vmcore.c                | 24 +++++++++---
 include/linux/crash_dump.h      |  3 ++
 kernel/kexec_core.c             | 14 +++++++
 7 files changed, 121 insertions(+), 25 deletions(-)

-- 
2.17.1