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Mark Rutland 4261a2e8b4 arm64: stackleak: fix current_top_of_stack() 
[ Upstream commit e85094c31d ]

Due to some historical confusion, arm64's current_top_of_stack() isn't
what the stackleak code expects. This could in theory result in a number
of problems, and practically results in an unnecessary performance hit.
We can avoid this by aligning the arm64 implementation with the x86
implementation.

The arm64 implementation of current_top_of_stack() was added
specifically for stackleak in commit:

  0b3e336601 ("arm64: Add support for STACKLEAK gcc plugin")

This was intended to be equivalent to the x86 implementation, but the
implementation, semantics, and performance characteristics differ
wildly:

* On x86, current_top_of_stack() returns the top of the current task's
  task stack, regardless of which stack is in active use.

  The implementation accesses a percpu variable which the x86 entry code
  maintains, and returns the location immediately above the pt_regs on
  the task stack (above which x86 has some padding).

* On arm64 current_top_of_stack() returns the top of the stack in active
  use (i.e. the one which is currently being used).

  The implementation checks the SP against a number of
  potentially-accessible stacks, and will BUG() if no stack is found.

The core stackleak_erase() code determines the upper bound of stack to
erase with:

| if (on_thread_stack())
|         boundary = current_stack_pointer;
| else
|         boundary = current_top_of_stack();

On arm64 stackleak_erase() is always called on a task stack, and
on_thread_stack() should always be true. On x86, stackleak_erase() is
mostly called on a trampoline stack, and is sometimes called on a task
stack.

Currently, this results in a lot of unnecessary code being generated for
arm64 for the impossible !on_thread_stack() case. Some of this is
inlined, bloating stackleak_erase(), while portions of this are left
out-of-line and permitted to be instrumented (which would be a
functional problem if that code were reachable).

As a first step towards improving this, this patch aligns arm64's
implementation of current_top_of_stack() with x86's, always returning
the top of the current task's stack. With GCC 11.1.0 this results in the
bulk of the unnecessary code being removed, including all of the
out-of-line instrumentable code.

While I don't believe there's a functional problem in practice I've
marked this as a fix since the semantic was clearly wrong, the fix
itself is simple, and other code might rely upon this in future.

Fixes: 0b3e336601 ("arm64: Add support for STACKLEAK gcc plugin")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Will Deacon <will@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-2-mark.rutland@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2022-06-09 10:25:48 +02:00
Documentation sched/psi: report zeroes for CPU full at the system level 2022-06-09 10:25:41 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
arch arm64: stackleak: fix current_top_of_stack() 2022-06-09 10:25:48 +02:00
block blk-throttle: Set BIO_THROTTLED when bio has been throttled 2022-06-09 10:25:29 +02:00
certs certs: Fix build error when CONFIG_MODULE_SIG_KEY is empty 2022-01-23 00:08:44 +09:00
crypto crypto: ecrdsa - Fix incorrect use of vli_cmp 2022-06-06 08:47:53 +02:00
drivers media: uvcvideo: Fix missing check to determine if element is found in list 2022-06-09 10:25:48 +02:00
fs fsnotify: fix wrong lockdep annotations 2022-06-09 10:25:43 +02:00
include x86/speculation: Add missing prototype for unpriv_ebpf_notify() 2022-06-09 10:25:44 +02:00
init kthread: Don't allocate kthread_struct for init and umh 2022-06-09 10:25:16 +02:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-04 09:25:05 -08:00
kernel printk: wake waiters for safe and NMI contexts 2022-06-09 10:25:42 +02:00
lib kunit: fix debugfs code to use enum kunit_status, not bool 2022-06-09 10:25:46 +02:00
mm zsmalloc: fix races between asynchronous zspage free and page migration 2022-06-06 08:47:53 +02:00
net nl80211: don't hold RTNL in color change request 2022-06-09 10:25:46 +02:00
samples samples/bpf, xdpsock: Fix race when running for fix duration of time 2022-04-08 13:58:18 +02:00
scripts kconfig: add fflush() before ferror() check 2022-05-25 09:58:59 +02:00
security lockdown: also lock down previous kgdb use 2022-05-25 09:59:10 +02:00
sound ASoC: rk3328: fix disabling mclk on pclk probe failure 2022-06-09 10:25:45 +02:00
tools perf tools: Use Python devtools for version autodetection rather than runtime 2022-06-09 10:25:46 +02:00
usr kbuild: remove include/linux/cyclades.h from header file check 2022-01-27 08:51:08 +01:00
virt KVM: Free new dirty bitmap if creating a new memslot fails 2022-05-25 09:59:03 +02:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap MAINTAINERS: Update Jisheng's email address 2022-03-08 17:30:32 +01:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS net: dsa: realtek-smi: move to subdirectory 2022-04-08 13:58:12 +02:00
Makefile Linux 5.17.13 2022-06-06 08:47:57 +02:00
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.