CVE-2024-35995

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

ACPI: CPPC: Use access_width over bit_width for system memory accesses

To align with ACPI 6.3+, since bit_width can be any 8-bit value, it
cannot be depended on to be always on a clean 8b boundary. This was
uncovered on the Cobalt 100 platform.

SError Interrupt on CPU26, code 0xbe000011 – SError
CPU: 26 PID: 1510 Comm: systemd-udevd Not tainted 5.15.2.1-13 #1
Hardware name: MICROSOFT CORPORATION, BIOS MICROSOFT CORPORATION
pstate: 62400009 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=–)
pc : cppc_get_perf_caps+0xec/0x410
lr : cppc_get_perf_caps+0xe8/0x410
sp : ffff8000155ab730
x29: ffff8000155ab730 x28: ffff0080139d0038 x27: ffff0080139d0078
x26: 0000000000000000 x25: ffff0080139d0058 x24: 00000000ffffffff
x23: ffff0080139d0298 x22: ffff0080139d0278 x21: 0000000000000000
x20: ffff00802b251910 x19: ffff0080139d0000 x18: ffffffffffffffff
x17: 0000000000000000 x16: ffffdc7e111bad04 x15: ffff00802b251008
x14: ffffffffffffffff x13: ffff013f1fd63300 x12: 0000000000000006
x11: ffffdc7e128f4420 x10: 0000000000000000 x9 : ffffdc7e111badec
x8 : ffff00802b251980 x7 : 0000000000000000 x6 : ffff0080139d0028
x5 : 0000000000000000 x4 : ffff0080139d0018 x3 : 00000000ffffffff
x2 : 0000000000000008 x1 : ffff8000155ab7a0 x0 : 0000000000000000
Kernel panic - not syncing: Asynchronous SError Interrupt
CPU: 26 PID: 1510 Comm: systemd-udevd Not tainted
5.15.2.1-13 #1
Hardware name: MICROSOFT CORPORATION, BIOS MICROSOFT CORPORATION
Call trace:
dump_backtrace+0x0/0x1e0
show_stack+0x24/0x30
dump_stack_lvl+0x8c/0xb8
dump_stack+0x18/0x34
panic+0x16c/0x384
add_taint+0x0/0xc0
arm64_serror_panic+0x7c/0x90
arm64_is_fatal_ras_serror+0x34/0xa4
do_serror+0x50/0x6c
el1h_64_error_handler+0x40/0x74
el1h_64_error+0x7c/0x80
cppc_get_perf_caps+0xec/0x410
cppc_cpufreq_cpu_init+0x74/0x400 [cppc_cpufreq]
cpufreq_online+0x2dc/0xa30
cpufreq_add_dev+0xc0/0xd4
subsys_interface_register+0x134/0x14c
cpufreq_register_driver+0x1b0/0x354
cppc_cpufreq_init+0x1a8/0x1000 [cppc_cpufreq]
do_one_initcall+0x50/0x250
do_init_module+0x60/0x27c
load_module+0x2300/0x2570
__do_sys_finit_module+0xa8/0x114
__arm64_sys_finit_module+0x2c/0x3c
invoke_syscall+0x78/0x100
el0_svc_common.constprop.0+0x180/0x1a0
do_el0_svc+0x84/0xa0
el0_svc+0x2c/0xc0
el0t_64_sync_handler+0xa4/0x12c
el0t_64_sync+0x1a4/0x1a8

Instead, use access_width to determine the size and use the offset and
width to shift and mask the bits to read/write out. Make sure to add a
check for system memory since pcc redefines the access_width to
subspace id.

If access_width is not set, then fall back to using bit_width.

[ rjw: Subject and changelog edits, comment adjustments ]