+ kcov-dont-lose-track-of-remote-references-during-softirqs.patch added to mm-nonmm-unstable branch

+ kcov-dont-lose-track-of-remote-references-during-softirqs.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: kcov: don't lose track of remote references during softirqs
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kcov-dont-lose-track-of-remote-references-during-softirqs.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kcov-dont-lose-track-of-remote-references-during-softirqs.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Aleksandr Nogikh <nogikh@google.com>
Subject: kcov: don't lose track of remote references during softirqs
Date: Tue, 11 Jun 2024 15:32:29 +0200

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.

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().

Link: https://lkml.kernel.org/r/20240611133229.527822-1-nogikh@google.com
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/kcov.h |    2 ++
 kernel/kcov.c        |    1 +
 2 files changed, 3 insertions(+)

--- a/include/linux/kcov.h~kcov-dont-lose-track-of-remote-references-during-softirqs
+++ a/include/linux/kcov.h
@@ -21,6 +21,8 @@ enum kcov_mode {
 	KCOV_MODE_TRACE_PC = 2,
 	/* Collecting comparison operands mode. */
 	KCOV_MODE_TRACE_CMP = 3,
+	/* The process owns a KCOV remote reference. */
+	KCOV_MODE_REMOTE = 4,
 };
 
 #define KCOV_IN_CTXSW	(1 << 30)
--- a/kernel/kcov.c~kcov-dont-lose-track-of-remote-references-during-softirqs
+++ a/kernel/kcov.c
@@ -632,6 +632,7 @@ static int kcov_ioctl_locked(struct kcov
 			return -EINVAL;
 		kcov->mode = mode;
 		t->kcov = kcov;
+		WRITE_ONCE(t->kcov_mode, KCOV_MODE_REMOTE);
 		kcov->t = t;
 		kcov->remote = true;
 		kcov->remote_size = remote_arg->area_size;
_

Patches currently in -mm which might be from nogikh@google.com are

kcov-dont-lose-track-of-remote-references-during-softirqs.patch