Subject: CVE-2022-48845: MIPS: smp: fill in sibling and core maps earlier

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

MIPS: smp: fill in sibling and core maps earlier

After enabling CONFIG_SCHED_CORE (landed during 5.14 cycle),
2-core 2-thread-per-core interAptiv (CPS-driven) started emitting
the following:

[    0.025698] CPU1 revision is: 0001a120 (MIPS interAptiv (multi))
[    0.048183] ------------[ cut here ]------------
[    0.048187] WARNING: CPU: 1 PID: 0 at kernel/sched/core.c:6025 sched_core_cpu_starting+0x198/0x240
[    0.048220] Modules linked in:
[    0.048233] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc3+ #35 b7b319f24073fd9a3c2aa7ad15fb7993eec0b26f
[    0.048247] Stack : 817f0000 00000004 327804c8 810eb050 00000000 00000004 00000000 c314fdd1
[    0.048278]         830cbd64 819c0000 81800000 817f0000 83070bf4 00000001 830cbd08 00000000
[    0.048307]         00000000 00000000 815fcbc4 00000000 00000000 00000000 00000000 00000000
[    0.048334]         00000000 00000000 00000000 00000000 817f0000 00000000 00000000 817f6f34
[    0.048361]         817f0000 818a3c00 817f0000 00000004 00000000 00000000 4dc33260 0018c933
[    0.048389]         ...
[    0.048396] Call Trace:
[    0.048399] [<8105a7bc>] show_stack+0x3c/0x140
[    0.048424] [<8131c2a0>] dump_stack_lvl+0x60/0x80
[    0.048440] [<8108b5c0>] __warn+0xc0/0xf4
[    0.048454] [<8108b658>] warn_slowpath_fmt+0x64/0x10c
[    0.048467] [<810bd418>] sched_core_cpu_starting+0x198/0x240
[    0.048483] [<810c6514>] sched_cpu_starting+0x14/0x80
[    0.048497] [<8108c0f8>] cpuhp_invoke_callback_range+0x78/0x140
[    0.048510] [<8108d914>] notify_cpu_starting+0x94/0x140
[    0.048523] [<8106593c>] start_secondary+0xbc/0x280
[    0.048539]
[    0.048543] ---[ end trace 0000000000000000 ]---
[    0.048636] Synchronize counters for CPU 1: done.

...for each but CPU 0/boot.
Basic debug printks right before the mentioned line say:

[    0.048170] CPU: 1, smt_mask:

So smt_mask, which is sibling mask obviously, is empty when entering
the function.
This is critical, as sched_core_cpu_starting() calculates
core-scheduling parameters only once per CPU start, and it's crucial
to have all the parameters filled in at that moment (at least it
uses cpu_smt_mask() which in fact is `&cpu_sibling_map[cpu]` on
MIPS).

A bit of debugging led me to that set_cpu_sibling_map() performing
the actual map calculation, was being invocated after
notify_cpu_start(), and exactly the latter function starts CPU HP
callback round (sched_core_cpu_starting() is basically a CPU HP
callback).
While the flow is same on ARM64 (maps after the notifier, although
before calling set_cpu_online()), x86 started calculating sibling
maps earlier than starting the CPU HP callbacks in Linux 4.14 (see
[0] for the reference). Neither me nor my brief tests couldn't find
any potential caveats in calculating the maps right after performing
delay calibration, but the WARN splat is now gone.
The very same debug prints now yield exactly what I expected from
them:

[    0.048433] CPU: 1, smt_mask: 0-1

[0] https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=76ce7cfe35ef

The Linux kernel CVE team has assigned CVE-2022-48845 to this issue.

Affected and fixed versions
===========================

	Fixed in 4.9.308 with commit 7315f8538db0
	Fixed in 4.14.273 with commit 32813321f18d
	Fixed in 4.19.236 with commit 56eaacb8137b
	Fixed in 5.4.186 with commit c2420bc33331
	Fixed in 5.10.107 with commit e8ad9ecc4069
	Fixed in 5.15.30 with commit be538b764a46
	Fixed in 5.16.16 with commit 94647aec80d0
	Fixed in 5.17 with commit f2703def339c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48845
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	arch/mips/kernel/smp.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/7315f8538db009605ffba00370678142ef00ac98
	https://git.kernel.org/stable/c/32813321f18d5432cec1b1a6ecc964f9ea26d565
	https://git.kernel.org/stable/c/56eaacb8137ba2071ce48d4e3d91979270e139a7
	https://git.kernel.org/stable/c/c2420bc3333111184cdcb112282d13afe1338dd7
	https://git.kernel.org/stable/c/e8ad9ecc406974deb5e7c070f51cc1d09d21dc4b
	https://git.kernel.org/stable/c/be538b764a46be1d0700fd3b6e82fb76bd17f13a
	https://git.kernel.org/stable/c/94647aec80d03d6914aa664b7b8e103cd9d63239
	https://git.kernel.org/stable/c/f2703def339c793674010cc9f01bfe4980231808