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
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------------------------------------------------------
From: Aleksandr Nogikh <nogikh@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Aleksandr Nogikh <nogikh@xxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
kcov-dont-lose-track-of-remote-references-during-softirqs.patch
