From f1bc96210c6a6b853b4b2eec808141956e8fbc5d Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Wed, 15 Jan 2020 17:25:12 +0100 Subject: [PATCH] kcsan: Make KCSAN compatible with lockdep We must avoid any recursion into lockdep if KCSAN is enabled on utilities used by lockdep. One manifestation of this is corruption of lockdep's IRQ trace state (if TRACE_IRQFLAGS), resulting in spurious warnings (see below). This commit fixes this by: 1. Using raw_local_irq{save,restore} in kcsan_setup_watchpoint(). 2. Disabling lockdep in kcsan_report(). Tested with: CONFIG_LOCKDEP=y CONFIG_DEBUG_LOCKDEP=y CONFIG_TRACE_IRQFLAGS=y This fix eliminates spurious warnings such as the following one: WARNING: CPU: 0 PID: 2 at kernel/locking/lockdep.c:4406 check_flags.part.0+0x101/0x220 Modules linked in: CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.5.0-rc1+ #11 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:check_flags.part.0+0x101/0x220 Call Trace: lock_is_held_type+0x69/0x150 freezer_fork+0x20b/0x370 cgroup_post_fork+0x2c9/0x5c0 copy_process+0x2675/0x3b40 _do_fork+0xbe/0xa30 ? _raw_spin_unlock_irqrestore+0x40/0x50 ? match_held_lock+0x56/0x250 ? kthread_park+0xf0/0xf0 kernel_thread+0xa6/0xd0 ? kthread_park+0xf0/0xf0 kthreadd+0x321/0x3d0 ? kthread_create_on_cpu+0x130/0x130 ret_from_fork+0x3a/0x50 irq event stamp: 64 hardirqs last enabled at (63): [] _raw_spin_unlock_irqrestore+0x40/0x50 hardirqs last disabled at (64): [] kcsan_setup_watchpoint+0x92/0x460 softirqs last enabled at (32): [] fpu__copy+0xe8/0x470 softirqs last disabled at (30): [] fpu__copy+0x69/0x470 Reported-by: Qian Cai Signed-off-by: Marco Elver Acked-by: Alexander Potapenko Tested-by: Qian Cai Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar --- kernel/kcsan/core.c | 6 ++++-- kernel/kcsan/report.c | 11 +++++++++++ kernel/locking/Makefile | 3 +++ 3 files changed, 18 insertions(+), 2 deletions(-) diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 87bf857c8893..64b30f7716a1 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -336,8 +336,10 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) * CPU-local data accesses), it makes more sense (from a data race * detection point of view) to simply disable preemptions to ensure * as many tasks as possible run on other CPUs. + * + * Use raw versions, to avoid lockdep recursion via IRQ flags tracing. */ - local_irq_save(irq_flags); + raw_local_irq_save(irq_flags); watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); if (watchpoint == NULL) { @@ -429,7 +431,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS); out_unlock: - local_irq_restore(irq_flags); + raw_local_irq_restore(irq_flags); out: user_access_restore(ua_flags); } diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c index b5b4feea49de..33bdf8b229b5 100644 --- a/kernel/kcsan/report.c +++ b/kernel/kcsan/report.c @@ -2,6 +2,7 @@ #include #include +#include #include #include #include @@ -410,6 +411,14 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, { unsigned long flags = 0; + /* + * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if + * we do not turn off lockdep here; this could happen due to recursion + * into lockdep via KCSAN if we detect a data race in utilities used by + * lockdep. + */ + lockdep_off(); + kcsan_disable_current(); if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) { if (print_report(ptr, size, access_type, value_change, cpu_id, type) && panic_on_warn) @@ -418,4 +427,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, release_report(&flags, type); } kcsan_enable_current(); + + lockdep_on(); } diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index 45452facff3b..6d11cfb9b41f 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -5,6 +5,9 @@ KCOV_INSTRUMENT := n obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o +# Avoid recursion lockdep -> KCSAN -> ... -> lockdep. +KCSAN_SANITIZE_lockdep.o := n + ifdef CONFIG_FUNCTION_TRACER CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_lockdep_proc.o = $(CC_FLAGS_FTRACE)