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Steven Rostedt (Google) bc17bc9643 ring-buffer: Fix a race in rb_time_cmpxchg() for 32 bit archs 
commit fff88fa0fb upstream.

Mathieu Desnoyers pointed out an issue in the rb_time_cmpxchg() for 32 bit
architectures. That is:

 static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
 {
	unsigned long cnt, top, bottom, msb;
	unsigned long cnt2, top2, bottom2, msb2;
	u64 val;

	/* The cmpxchg always fails if it interrupted an update */
	 if (!__rb_time_read(t, &val, &cnt2))
		 return false;

	 if (val != expect)
		 return false;

<<<< interrupted here!

	 cnt = local_read(&t->cnt);

The problem is that the synchronization counter in the rb_time_t is read
*after* the value of the timestamp is read. That means if an interrupt
were to come in between the value being read and the counter being read,
it can change the value and the counter and the interrupted process would
be clueless about it!

The counter needs to be read first and then the value. That way it is easy
to tell if the value is stale or not. If the counter hasn't been updated,
then the value is still good.

Link: https://lore.kernel.org/linux-trace-kernel/20231211201324.652870-1-mathieu.desnoyers@efficios.com/
Link: https://lore.kernel.org/linux-trace-kernel/20231212115301.7a9c9a64@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Fixes: 10464b4aa6 ("ring-buffer: Add rb_time_t 64 bit operations for speeding up 32 bit")
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-12-20 17:02:06 +01:00
arch kexec: drop dependency on ARCH_SUPPORTS_KEXEC from CRASH_DUMP 2023-12-20 17:02:03 +01:00
block blk-cgroup: bypass blkcg_deactivate_policy after destroying 2023-12-20 17:01:55 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: pcrypt - Fix hungtask for PADATA_RESET 2023-11-28 17:19:42 +00:00
Documentation tee: optee: Fix supplicant based device enumeration 2023-12-13 18:45:11 +01:00
drivers drm/i915: Fix remapped stride with CCS on ADL+ 2023-12-20 17:02:04 +01:00
fs smb: client: fix OOB in smb2_query_reparse_point() 2023-12-20 17:02:05 +01:00
include mm/mglru: reclaim offlined memcgs harder 2023-12-20 17:02:03 +01:00
init proc: sysctl: prevent aliased sysctls from getting passed to init 2023-11-28 17:19:57 +00:00
io_uring io_uring/cmd: fix breakage in SOCKET_URING_OP_SIOC* implementation 2023-12-20 17:01:52 +01:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel ring-buffer: Fix a race in rb_time_cmpxchg() for 32 bit archs 2023-12-20 17:02:06 +01:00
lib cred: get rid of CONFIG_DEBUG_CREDENTIALS 2023-12-20 17:01:51 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/shmem: fix race in shmem_undo_range w/THP 2023-12-20 17:02:03 +01:00
net rxrpc: Fix some minor issues with bundle tracing 2023-12-20 17:01:55 +01:00
rust rust: docs: fix logo replacement 2023-10-19 16:40:00 +02:00
samples samples/bpf: syscall_tp_user: Fix array out-of-bound access 2023-11-28 17:19:48 +00:00
scripts scripts/checkstack.pl: match all stack sizes for s390 2023-12-20 17:01:59 +01:00
security cred: get rid of CONFIG_DEBUG_CREDENTIALS 2023-12-20 17:01:51 +01:00
sound ALSA: hda/tas2781: reset the amp before component_add 2023-12-20 17:01:53 +01:00
tools Revert "selftests: error out if kernel header files are not yet built" 2023-12-20 17:02:01 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.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 USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
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 Char/Misc driver fixes for 6.6-final 2023-10-28 07:51:27 -10:00
Makefile Linux 6.6.7 2023-12-13 18:45:36 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.