On 6/15/23 08:37, Michael Ellerman wrote:
The TPM code in prom_init.c creates a small buffer of memory to store
the TPM's SML (Stored Measurement Log). It's communicated to Linux via
the linux,sml-base/size device tree properties of the TPM node.
When kexec'ing that buffer can be overwritten, or when kdump'ing it may
not be mapped by the second kernel. The latter can lead to a crash when
booting the second kernel such as:
tpm_ibmvtpm 71000003: CRQ initialization completed
BUG: Unable to handle kernel data access on read at 0xc00000002ffb0000
Faulting instruction address: 0xc0000000200a70e0
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.2.0-rc2-00134-g9307ce092f5d #314
Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1200 0xf000005 of:SLOF,git-5b4c5a pSeries
NIP: c0000000200a70e0 LR: c0000000203dd5dc CTR: 0000000000000800
REGS: c000000024543280 TRAP: 0300 Not tainted (6.2.0-rc2-00134-g9307ce092f5d)
MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 24002280 XER: 00000006
CFAR: c0000000200a70c8 DAR: c00000002ffb0000 DSISR: 40000000 IRQMASK: 0
...
NIP memcpy_power7+0x400/0x7d0
LR kmemdup+0x5c/0x80
Call Trace:
memcpy_power7+0x274/0x7d0 (unreliable)
kmemdup+0x5c/0x80
tpm_read_log_of+0xe8/0x1b0
tpm_bios_log_setup+0x60/0x210
tpm_chip_register+0x134/0x320
tpm_ibmvtpm_probe+0x520/0x7d0
vio_bus_probe+0x9c/0x460
really_probe+0x104/0x420
__driver_probe_device+0xb0/0x170
driver_probe_device+0x58/0x180
__driver_attach+0xd8/0x250
bus_for_each_dev+0xb4/0x140
driver_attach+0x34/0x50
bus_add_driver+0x1e8/0x2d0
driver_register+0xb4/0x1c0
__vio_register_driver+0x74/0x9c
ibmvtpm_module_init+0x34/0x48
do_one_initcall+0x80/0x320
kernel_init_freeable+0x304/0x3ac
kernel_init+0x30/0x1a0
ret_from_kernel_thread+0x5c/0x64
To fix the crash, add the SML region to the usable memory areas for the
kdump kernel, so that the second kernel will map the region. To avoid
corruption of the region, add the region to the reserved memory areas,
To me the 2nd paragraph and the one below seem to say that in general it does NOT 'avoid corruption of the region.'
so that the second kernel does not use the memory for something else.
Note that when loading a kdump kernel with the regular kexec_load()
syscall the SML may be overwritten by the kdump kernel, depending on
where the SML is in memory in relation to the crashkernel region. That
is a separate problem that is not solved by this patch.
Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
Reported-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
I agree to the code:
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
