linux.git/kernel/kcov.c, branch v6.12.81

kcov: mark in_softirq_really() as __always_inline

2025-01-09T12:33:49+00:00

commit cb0ca08b326aa03f87fe94bb91872ce8d2ef1ed8 upstream.

If gcc decides not to inline in_softirq_really(), objtool warns about a
function call with UACCESS enabled:

kernel/kcov.o: warning: objtool: __sanitizer_cov_trace_pc+0x1e: call to in_softirq_really() with UACCESS enabled
kernel/kcov.o: warning: objtool: check_kcov_mode+0x11: call to in_softirq_really() with UACCESS enabled

Mark this as __always_inline to avoid the problem.

Link: https://lkml.kernel.org/r/20241217071814.2261620-1-arnd@kernel.org
Fixes: 7d4df2dad312 ("kcov: properly check for softirq context")
Signed-off-by: Arnd Bergmann 
Reviewed-by: Marco Elver 
Cc: Aleksandr Nogikh 
Cc: Andrey Konovalov 
Cc: Dmitry Vyukov 
Cc: Josh Poimboeuf 
Cc: Peter Zijlstra 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Greg Kroah-Hartman

Merge tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2024-09-17T10:40:34+00:00

Pull x86 build updates from Thomas Gleixner:
 "Updates for KCOV instrumentation on x86:

   - Prevent spurious KCOV coverage in common_interrupt()

   - Fixup the KCOV Makefile directive which got stale due to a source
     file rename

   - Exclude stack unwinding from KCOV as it creates large amounts of
     uninteresting coverage

   - Provide a self test to validate that KCOV coverage of the interrupt
     handling code starts not before preempt count got updated"

* tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86: Ignore stack unwinding in KCOV
  module: Fix KCOV-ignored file name
  kcov: Add interrupt handling self test
  x86/entry: Remove unwanted instrumentation in common_interrupt()

kcov: Add interrupt handling self test

2024-08-08T15:36:35+00:00

Add a boot self test that can catch sprious coverage from interrupts.
The coverage callback filters out interrupt code, but only after the
handler updates preempt count. Some code periodically leaks out
of that section and leads to spurious coverage.
Add a best-effort (but simple) test that is likely to catch such bugs.
If the test is enabled on CI systems that use KCOV, they should catch
any issues fast.

Signed-off-by: Dmitry Vyukov 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexander Potapenko 
Reviewed-by: Marco Elver 
Reviewed-by: Andrey Konovalov 
Link: https://lore.kernel.org/all/7662127c97e29da1a748ad1c1539dd7b65b737b2.1718092070.git.dvyukov@google.com

kcov: properly check for softirq context

2024-08-08T01:33:56+00:00

When collecting coverage from softirqs, KCOV uses in_serving_softirq() to
check whether the code is running in the softirq context.  Unfortunately,
in_serving_softirq() is > 0 even when the code is running in the hardirq
or NMI context for hardirqs and NMIs that happened during a softirq.

As a result, if a softirq handler contains a remote coverage collection
section and a hardirq with another remote coverage collection section
happens during handling the softirq, KCOV incorrectly detects a nested
softirq coverate collection section and prints a WARNING, as reported by
syzbot.

This issue was exposed by commit a7f3813e589f ("usb: gadget: dummy_hcd:
Switch to hrtimer transfer scheduler"), which switched dummy_hcd to using
hrtimer and made the timer's callback be executed in the hardirq context.

Change the related checks in KCOV to account for this behavior of
in_serving_softirq() and make KCOV ignore remote coverage collection
sections in the hardirq and NMI contexts.

This prevents the WARNING printed by syzbot but does not fix the inability
of KCOV to collect coverage from the __usb_hcd_giveback_urb when dummy_hcd
is in use (caused by a7f3813e589f); a separate patch is required for that.

Link: https://lkml.kernel.org/r/20240729022158.92059-1-andrey.konovalov@linux.dev
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Andrey Konovalov 
Reported-by: syzbot+2388cdaeb6b10f0c13ac@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2388cdaeb6b10f0c13ac
Acked-by: Marco Elver 
Cc: Alan Stern 
Cc: Aleksandr Nogikh 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Greg Kroah-Hartman 
Cc: Marcello Sylvester Bauer 
Cc: 
Signed-off-by: Andrew Morton

kcov: don't lose track of remote references during softirqs

2024-06-15T17:43:08+00:00

In kcov_remote_start()/kcov_remote_stop(), we swap the previous KCOV
metadata of the current task into a per-CPU variable.  However, the
kcov_mode_enabled(mode) check is not sufficient in the case of remote KCOV
coverage: current->kcov_mode always remains KCOV_MODE_DISABLED for remote
KCOV objects.

If the original task that has invoked the KCOV_REMOTE_ENABLE ioctl happens
to get interrupted and kcov_remote_start() is called, it ultimately leads
to kcov_remote_stop() NOT restoring the original KCOV reference.  So when
the task exits, all registered remote KCOV handles remain active forever.

The most uncomfortable effect (at least for syzkaller) is that the bug
prevents the reuse of the same /sys/kernel/debug/kcov descriptor.  If
we obtain it in the parent process and then e.g.  drop some
capabilities and continuously fork to execute individual programs, at
some point current->kcov of the forked process is lost,
kcov_task_exit() takes no action, and all KCOV_REMOTE_ENABLE ioctls
calls from subsequent forks fail.

And, yes, the efficiency is also affected if we keep on losing remote
kcov objects.
a) kcov_remote_map keeps on growing forever.
b) (If I'm not mistaken), we're also not freeing the memory referenced
by kcov->area.

Fix it by introducing a special kcov_mode that is assigned to the task
that owns a KCOV remote object.  It makes kcov_mode_enabled() return true
and yet does not trigger coverage collection in __sanitizer_cov_trace_pc()
and write_comp_data().

[nogikh@google.com: replace WRITE_ONCE() with an ordinary assignment]
  Link: https://lkml.kernel.org/r/20240614171221.2837584-1-nogikh@google.com
Link: https://lkml.kernel.org/r/20240611133229.527822-1-nogikh@google.com
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Aleksandr Nogikh 
Reviewed-by: Dmitry Vyukov 
Reviewed-by: Andrey Konovalov 
Tested-by: Andrey Konovalov 
Cc: Alexander Potapenko 
Cc: Arnd Bergmann 
Cc: Marco Elver 
Cc: 
Signed-off-by: Andrew Morton

kcov: avoid clang out-of-range warning

2024-04-26T04:07:04+00:00

The area_size is never larger than the maximum on 64-bit architectutes:

kernel/kcov.c:634:29: error: result of comparison of constant 1152921504606846975 with expression of type '__u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
                if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
                    ~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The compiler can correctly optimize the check away and the code appears
correct to me, so just add a cast to avoid the warning.

Link: https://lkml.kernel.org/r/20240328143051.1069575-5-arnd@kernel.org
Signed-off-by: Arnd Bergmann 
Reviewed-by: Justin Stitt 
Cc: Andrey Konovalov 
Cc: Bill Wendling 
Cc: Dmitry Vyukov 
Cc: Nathan Chancellor 
Cc: Nick Desaulniers 
Signed-off-by: Andrew Morton

kcov: add prototypes for helper functions

2023-06-10T00:44:17+00:00

A number of internal functions in kcov are only called from generated code
and don't technically need a declaration, but 'make W=1' warns about
global symbols without a prototype:

kernel/kcov.c:199:14: error: no previous prototype for '__sanitizer_cov_trace_pc' [-Werror=missing-prototypes]
kernel/kcov.c:264:14: error: no previous prototype for '__sanitizer_cov_trace_cmp1' [-Werror=missing-prototypes]
kernel/kcov.c:270:14: error: no previous prototype for '__sanitizer_cov_trace_cmp2' [-Werror=missing-prototypes]
kernel/kcov.c:276:14: error: no previous prototype for '__sanitizer_cov_trace_cmp4' [-Werror=missing-prototypes]
kernel/kcov.c:282:14: error: no previous prototype for '__sanitizer_cov_trace_cmp8' [-Werror=missing-prototypes]
kernel/kcov.c:288:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp1' [-Werror=missing-prototypes]
kernel/kcov.c:295:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp2' [-Werror=missing-prototypes]
kernel/kcov.c:302:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp4' [-Werror=missing-prototypes]
kernel/kcov.c:309:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp8' [-Werror=missing-prototypes]
kernel/kcov.c:316:14: error: no previous prototype for '__sanitizer_cov_trace_switch' [-Werror=missing-prototypes]

Adding prototypes for these in a header solves that problem, but now there
is a mismatch between the built-in type and the prototype on 64-bit
architectures because they expect some functions to take a 64-bit
'unsigned long' argument rather than an 'unsigned long long' u64 type:

include/linux/kcov.h:84:6: error: conflicting types for built-in function '__sanitizer_cov_trace_switch'; expected 'void(long long unsigned int,  void *)' [-Werror=builtin-declaration-mismatch]
   84 | void __sanitizer_cov_trace_switch(u64 val, u64 *cases);
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Avoid this as well with a custom type definition.

Link: https://lkml.kernel.org/r/20230517124944.929997-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann 
Cc: Andrey Konovalov 
Cc: Dmitry Vyukov 
Cc: Rong Tao 
Signed-off-by: Andrew Morton

mm: replace vma->vm_flags direct modifications with modifier calls

2023-02-10T00:51:39+00:00

Replace direct modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness.

[akpm@linux-foundation.org: fix drivers/misc/open-dice.c, per Hyeonggon Yoo]
Link: https://lkml.kernel.org/r/20230126193752.297968-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Michal Hocko 
Acked-by: Mel Gorman 
Acked-by: Mike Rapoport (IBM) 
Acked-by: Sebastian Reichel 
Reviewed-by: Liam R. Howlett 
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Andy Lutomirski 
Cc: Arjun Roy 
Cc: Axel Rasmussen 
Cc: David Hildenbrand 
Cc: David Howells 
Cc: Davidlohr Bueso 
Cc: David Rientjes 
Cc: Eric Dumazet 
Cc: Greg Thelen 
Cc: Hugh Dickins 
Cc: Ingo Molnar 
Cc: Jann Horn 
Cc: Joel Fernandes 
Cc: Johannes Weiner 
Cc: Kent Overstreet 
Cc: Laurent Dufour 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox 
Cc: Minchan Kim 
Cc: Paul E. McKenney 
Cc: Peter Oskolkov 
Cc: Peter Xu 
Cc: Peter Zijlstra 
Cc: Punit Agrawal 
Cc: Sebastian Andrzej Siewior 
Cc: Shakeel Butt 
Cc: Soheil Hassas Yeganeh 
Cc: Song Liu 
Cc: Vlastimil Babka 
Cc: Will Deacon 
Signed-off-by: Andrew Morton

kcov: kmsan: unpoison area->list in kcov_remote_area_put()

2022-10-03T21:03:23+00:00

KMSAN does not instrument kernel/kcov.c for performance reasons (with
CONFIG_KCOV=y virtually every place in the kernel invokes kcov
instrumentation).  Therefore the tool may miss writes from kcov.c that
initialize memory.

When CONFIG_DEBUG_LIST is enabled, list pointers from kernel/kcov.c are
passed to instrumented helpers in lib/list_debug.c, resulting in false
positives.

To work around these reports, we unpoison the contents of area->list after
initializing it.

Link: https://lkml.kernel.org/r/20220915150417.722975-30-glider@google.com
Signed-off-by: Alexander Potapenko 
Cc: Alexander Viro 
Cc: Alexei Starovoitov 
Cc: Andrey Konovalov 
Cc: Andrey Konovalov 
Cc: Andy Lutomirski 
Cc: Arnd Bergmann 
Cc: Borislav Petkov 
Cc: Christoph Hellwig 
Cc: Christoph Lameter 
Cc: David Rientjes 
Cc: Dmitry Vyukov 
Cc: Eric Biggers 
Cc: Eric Biggers 
Cc: Eric Dumazet 
Cc: Greg Kroah-Hartman 
Cc: Herbert Xu 
Cc: Ilya Leoshkevich 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Joonsoo Kim 
Cc: Kees Cook 
Cc: Marco Elver 
Cc: Mark Rutland 
Cc: Matthew Wilcox 
Cc: Michael S. Tsirkin 
Cc: Pekka Enberg 
Cc: Peter Zijlstra 
Cc: Petr Mladek 
Cc: Stephen Rothwell 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Vasily Gorbik 
Cc: Vegard Nossum 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

kcov: update pos before writing pc in trace function

2022-05-25T20:05:42+00:00

In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
However, some early interrupt code could bypass check_kcov_mode() check
and invoke __sanitizer_cov_trace_pc().  If such interrupt is raised
between writing pc and updating pos, the pc could be overitten by the
recursive __sanitizer_cov_trace_pc().

As suggested by Dmitry, we cold update pos before writing pc to avoid such
interleaving.

Apply the same change to write_comp_data().

Link: https://lkml.kernel.org/r/20220523053531.1572793-1-liu3101@purdue.edu
Signed-off-by: Congyu Liu 
Reviewed-by: Dmitry Vyukov 
Cc: Andrey Konovalov 
Signed-off-by: Andrew Morton