x86/resctrl: Clear staged_config[] before and after it is used

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

x86/resctrl: Clear staged_config[] before and after it is used

As a temporary storage, staged_config[] in rdt_domain should be cleared

before and after it is used. The stale value in staged_config[] could

cause an MSR access error.

Here is a reproducer on a system with 16 usable CLOSIDs for a 15-way L3

Cache (MBA should be disabled if the number of CLOSIDs for MB is less than

16.) :

mount -t resctrl resctrl -o cdp /sys/fs/resctrl

mkdir /sys/fs/resctrl/p{1..7}

umount /sys/fs/resctrl/

mount -t resctrl resctrl /sys/fs/resctrl

mkdir /sys/fs/resctrl/p{1..8}

An error occurs when creating resource group named p8:

unchecked MSR access error: WRMSR to 0xca0 (tried to write 0x00000000000007ff) at rIP: 0xffffffff82249142 (cat_wrmsr+0x32/0x60)

Call Trace:

<IRQ>

__flush_smp_call_function_queue+0x11d/0x170

__sysvec_call_function+0x24/0xd0

sysvec_call_function+0x89/0xc0

</IRQ>

<TASK>

asm_sysvec_call_function+0x16/0x20

When creating a new resource control group, hardware will be configured

by the following process:

rdtgroup_mkdir()

rdtgroup_mkdir_ctrl_mon()

rdtgroup_init_alloc()

resctrl_arch_update_domains()

resctrl_arch_update_domains() iterates and updates all resctrl_conf_type

whose have_new_ctrl is true. Since staged_config[] holds the same values as

when CDP was enabled, it will continue to update the CDP_CODE and CDP_DATA

configurations. When group p8 is created, get_config_index() called in

resctrl_arch_update_domains() will return 16 and 17 as the CLOSIDs for

CDP_CODE and CDP_DATA, which will be translated to an invalid register -

0xca0 in this scenario.

Fix it by clearing staged_config[] before and after it is used.

[reinette: re-order commit tags]