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![]() Currently, load_microcode_amd() iterates over all NUMA nodes, retrieves their
CPU masks and unconditionally accesses per-CPU data for the first CPU of each
mask.
According to Documentation/admin-guide/mm/numaperf.rst:
"Some memory may share the same node as a CPU, and others are provided as
memory only nodes."
Therefore, some node CPU masks may be empty and wouldn't have a "first CPU".
On a machine with far memory (and therefore CPU-less NUMA nodes):
- cpumask_of_node(nid) is 0
- cpumask_first(0) is CONFIG_NR_CPUS
- cpu_data(CONFIG_NR_CPUS) accesses the cpu_info per-CPU array at an
index that is 1 out of bounds
This does not have any security implications since flashing microcode is
a privileged operation but I believe this has reliability implications by
potentially corrupting memory while flashing a microcode update.
When booting with CONFIG_UBSAN_BOUNDS=y on an AMD machine that flashes
a microcode update. I get the following splat:
UBSAN: array-index-out-of-bounds in arch/x86/kernel/cpu/microcode/amd.c:X:Y
index 512 is out of range for type 'unsigned long[512]'
[...]
Call Trace:
dump_stack
__ubsan_handle_out_of_bounds
load_microcode_amd
request_microcode_amd
reload_store
kernfs_fop_write_iter
vfs_write
ksys_write
do_syscall_64
entry_SYSCALL_64_after_hwframe
Change the loop to go over only NUMA nodes which have CPUs before determining
whether the first CPU on the respective node needs microcode update.
[ bp: Massage commit message, fix typo. ]
Fixes:
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||
---|---|---|
.. | ||
mce | ||
microcode | ||
mtrr | ||
resctrl | ||
sgx | ||
.gitignore | ||
acrn.c | ||
amd.c | ||
aperfmperf.c | ||
bugs.c | ||
bus_lock.c | ||
cacheinfo.c | ||
centaur.c | ||
common.c | ||
cpu.h | ||
cpuid-deps.c | ||
cyrix.c | ||
debugfs.c | ||
feat_ctl.c | ||
hygon.c | ||
hypervisor.c | ||
intel_epb.c | ||
intel.c | ||
Makefile | ||
match.c | ||
mkcapflags.sh | ||
mshyperv.c | ||
perfctr-watchdog.c | ||
powerflags.c | ||
proc.c | ||
rdrand.c | ||
scattered.c | ||
topology_amd.c | ||
topology_common.c | ||
topology_ext.c | ||
topology.c | ||
topology.h | ||
transmeta.c | ||
tsx.c | ||
umc.c | ||
umwait.c | ||
vmware.c | ||
vortex.c | ||
zhaoxin.c |