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Mateusz Jończyk 0bf083a803 mips/math-emu: fix emulation of the prefx instruction 
commit 42a39e4aa5 upstream.

Currently, installation of Debian 12.8 for mipsel fails on machines
without an FPU [1]. This is caused by the fact that zstd (which is used
for initramfs compression) executes the prefx instruction, which is not
emulated properly by the kernel.

The prefx (Prefetch Indexed) instruction fetches data from memory into
the cache without any side effects. Though functionally unrelated, it
requires an FPU [2].

Bytecode format of this instruction ends on "001111" binary:

	(prefx instruction format) & 0x0000003f = 0x0000000f

The code in fpux_emu() runs like so:

	#define MIPSInst(x) x
	#define MIPSInst_FMA_FFMT(x) (MIPSInst(x) & 0x00000007)
	#define MIPSInst_FUNC(x) (MIPSInst(x) & 0x0000003f)
	enum cop1x_func { ..., pfetch_op = 0x0f, ... };

	...

	switch (MIPSInst_FMA_FFMT(ir)) {
	...

	case 0x3:
		if (MIPSInst_FUNC(ir) != pfetch_op)
			return SIGILL;

		/* ignore prefx operation */
		break;

	default:
		return SIGILL;
	}

That snippet above contains a logic error and the
	if (MIPSInst_FUNC(ir) != pfetch_op)
comparison always fires.

When MIPSInst_FUNC(ir) is equal to pfetch_op, ir must end on 001111
binary. In this case, MIPSInst_FMA_FFMT(ir) must be equal to 0x7, which
does not match that case label.

This causes emulation failure for the prefx instruction. Fix it.

This has been broken by
commit 919af8b96c ("MIPS: Make definitions of MIPSInst_FMA_{FUNC,FMTM} consistent with MIPS64 manual")
which modified the MIPSInst_FMA_FFMT macro without updating the users.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: stable@vger.kernel.org # after 3 weeks
Cc: Dengcheng Zhu <dzhu@wavecomp.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Ming Wang <wangming01@loongson.cn>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Fixes: 919af8b96c ("MIPS: Make definitions of MIPSInst_FMA_{FUNC,FMTM} consistent with MIPS64 manual")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1091858
[2] MIPS Architecture For Programmers Volume II-A: The MIPS32 Instruction Set

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
History 2025-02-17 10:05:19 +01:00
arch mips/math-emu: fix emulation of the prefx instruction 2025-02-17 10:05:19 +01:00
block blk-cgroup: Fix class @block_class's subsystem refcount leakage 2025-02-17 10:05:12 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: api - Fix boot-up self-test race 2025-02-08 09:57:28 +01:00
Documentation arm64: Filter out SVE hwcaps when FEAT_SVE isn't implemented 2025-02-17 10:05:04 +01:00
drivers dm-crypt: track tag_offset in convert_context 2025-02-17 10:05:19 +01:00
fs ksmbd: fix integer overflows on 32 bit systems 2025-02-17 10:05:06 +01:00
include scsi: ufs: core: Fix the HIGH/LOW_TEMP Bit Definitions 2025-02-17 10:05:12 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-05 14:02:45 +01:00
io_uring io_uring/uring_cmd: use cached cmd_op in io_uring_cmd_sock() 2025-02-08 09:58:10 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel ring-buffer: Do not allow events in NMI with generic atomic64 cmpxchg() 2025-02-17 10:05:14 +01:00
lib atomic64: Use arch_spin_locks instead of raw_spin_locks 2025-02-17 10:05:14 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm memcg: fix soft lockup in the OOM process 2025-02-08 09:58:19 +01:00
net Bluetooth: L2CAP: accept zero as a special value for MTU auto-selection 2025-02-17 10:05:09 +01:00
rust rust: kbuild: set bindgen's Rust target version 2024-12-19 18:13:22 +01:00
samples samples/landlock: Fix possible NULL dereference in parse_path() 2025-02-08 09:57:11 +01:00
scripts kbuild: switch from lz4c to lz4 for compression 2025-02-08 09:58:12 +01:00
security KEYS: trusted: dcp: fix improper sg use with CONFIG_VMAP_STACK=y 2025-02-17 10:05:09 +01:00
sound ASoC: acp: Support microphone from Lenovo Go S 2025-02-17 10:05:18 +01:00
tools perf bench: Fix undefined behavior in cmpworker() 2025-02-17 10:05:12 +01:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: update location of media main tree 2024-12-05 14:02:42 +01:00
Makefile Linux 6.12.13 2025-02-08 09:58:20 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.