🛡️ CVE-2024-56617 — kernel

cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU

In the Linux kernel, the following vulnerability has been resolved:

cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU

Commit

5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")

adds functionality that architectures can use to optionally allocate and

build cacheinfo early during boot. Commit

6539cffa9495 ("cacheinfo: Add arch specific early level initializer")

lets secondary CPUs correct (and reallocate memory) cacheinfo data if

needed.

If the early build functionality is not used and cacheinfo does not need

correction, memory for cacheinfo is never allocated. x86 does not use

the early build functionality. Consequently, during the cacheinfo CPU

hotplug callback, last_level_cache_is_valid() attempts to dereference

a NULL pointer:

BUG: kernel NULL pointer dereference, address: 0000000000000100

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not present page

PGD 0 P4D 0

Oops: 0000 [#1] PREEPMT SMP NOPTI

CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1

RIP: 0010: last_level_cache_is_valid+0x95/0xe0a

Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback

if not done earlier.

Moreover, before determining the validity of the last-level cache info,

ensure that it has been allocated. Simply checking for non-zero

cache_leaves() is not sufficient, as some architectures (e.g., Intel

processors) have non-zero cache_leaves() before allocation.

Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().

This function iterates over all online CPUs. However, a CPU may have come

online recently, but its cacheinfo may not have been allocated yet.

While here, remove an unnecessary indentation in allocate_cache_info().

[ bp: Massage. ]