[patch 59/86] lib/ubsan: don't serialize UBSAN report

Andrew Morton
2019-12-05T00:52:57Z

From: Julien Grall <julien.grall@arm.com>
Subject: lib/ubsan: don't serialize UBSAN report

At the moment, UBSAN report will be serialized using a spin_lock(). On
RT-systems, spinlocks are turned to rt_spin_lock and may sleep. This will
result to the following splat if the undefined behavior is in a context
that can sleep:

[ 6951.484876] BUG: sleeping function called from invalid context at /src/linux/kernel/locking/rtmutex.c:968
[ 6951.484882] in_atomic(): 1, irqs_disabled(): 128, pid: 3447, name: make
[ 6951.484884] 1 lock held by make/3447:
[ 6951.484885] #0: 000000009a966332 (&mm->mmap_sem){++++}, at: do_page_fault+0x140/0x4f8
[ 6951.484895] irq event stamp: 6284
[ 6951.484896] hardirqs last enabled at (6283): [<ffff000011326520>] _raw_spin_unlock_irqrestore+0x90/0xa0
[ 6951.484901] hardirqs last disabled at (6284): [<ffff0000113262b0>] _raw_spin_lock_irqsave+0x30/0x78
[ 6951.484902] softirqs last enabled at (2430): [<ffff000010088ef8>] fpsimd_restore_current_state+0x60/0xe8
[ 6951.484905] softirqs last disabled at (2427): [<ffff000010088ec0>] fpsimd_restore_current_state+0x28/0xe8
[ 6951.484907] Preemption disabled at:
[ 6951.484907] [<ffff000011324a4c>] rt_mutex_futex_unlock+0x4c/0xb0
[ 6951.484911] CPU: 3 PID: 3447 Comm: make Tainted: G W 5.2.14-rt7-01890-ge6e057589653 #911
[ 6951.484913] Call trace:
[ 6951.484913] dump_backtrace+0x0/0x148
[ 6951.484915] show_stack+0x14/0x20
[ 6951.484917] dump_stack+0xbc/0x104
[ 6951.484919] ___might_sleep+0x154/0x210
[ 6951.484921] rt_spin_lock+0x68/0xa0
[ 6951.484922] ubsan_prologue+0x30/0x68
[ 6951.484924] handle_overflow+0x64/0xe0
[ 6951.484926] __ubsan_handle_add_overflow+0x10/0x18
[ 6951.484927] __lock_acquire+0x1c28/0x2a28
[ 6951.484929] lock_acquire+0xf0/0x370
[ 6951.484931] _raw_spin_lock_irqsave+0x58/0x78
[ 6951.484932] rt_mutex_futex_unlock+0x4c/0xb0
[ 6951.484933] rt_spin_unlock+0x28/0x70
[ 6951.484934] get_page_from_freelist+0x428/0x2b60
[ 6951.484936] __alloc_pages_nodemask+0x174/0x1708
[ 6951.484938] alloc_pages_vma+0x1ac/0x238
[ 6951.484940] __handle_mm_fault+0x4ac/0x10b0
[ 6951.484941] handle_mm_fault+0x1d8/0x3b0
[ 6951.484942] do_page_fault+0x1c8/0x4f8
[ 6951.484943] do_translation_fault+0xb8/0xe0
[ 6951.484945] do_mem_abort+0x3c/0x98
[ 6951.484946] el0_da+0x20/0x24

The spin_lock() will protect against multiple CPUs to output a report
together, I guess to prevent them from being interleaved. However, they
can still interleave with other messages (and even splat from
__might_sleep).

So the lock usefulness seems pretty limited. Rather than trying to
accomodate RT-system by switching to a raw_spin_lock(), the lock is now
completely dropped.

Link: http://lkml.kernel.org/r/20190920100835.14999-1-julien.grall@arm.com
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reported-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

lib/ubsan.c | 64 +++++++++++++++++---------------------------------
1 file changed, 23 insertions(+), 41 deletions(-)

--- a/lib/ubsan.c~lib-ubsan-dont-seralize-ubsan-report
+++ a/lib/ubsan.c
@@ -140,25 +140,21 @@ static void val_to_string(char *str, siz
}
}

-static DEFINE_SPINLOCK(report_lock);
-
-static void ubsan_prologue(struct source_location *location,
- unsigned long *flags)
+static void ubsan_prologue(struct source_location *location)
{
current->in_ubsan++;
- spin_lock_irqsave(&report_lock, *flags);

pr_err("========================================"
"========================================\n");
print_source_location("UBSAN: Undefined behaviour in", location);
}

-static void ubsan_epilogue(unsigned long *flags)
+static void ubsan_epilogue(void)
{
dump_stack();
pr_err("========================================"
"========================================\n");
- spin_unlock_irqrestore(&report_lock, *flags);
+
current->in_ubsan--;
}

@@ -167,14 +163,13 @@ static void handle_overflow(struct overf
{

struct type_descriptor *type = data->type;
- unsigned long flags;
char lhs_val_str[VALUE_LENGTH];
char rhs_val_str[VALUE_LENGTH];

if (suppress_report(&data->location))
return;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(lhs_val_str, sizeof(lhs_val_str), type, lhs);
val_to_string(rhs_val_str, sizeof(rhs_val_str), type, rhs);
@@ -186,7 +181,7 @@ static void handle_overflow(struct overf
rhs_val_str,
type->type_name);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}

void __ubsan_handle_add_overflow(struct overflow_data *data,
@@ -214,20 +209,19 @@ EXPORT_SYMBOL(__ubsan_handle_mul_overflo
void __ubsan_handle_negate_overflow(struct overflow_data *data,
void *old_val)
{
- unsigned long flags;
char old_val_str[VALUE_LENGTH];

if (suppress_report(&data->location))
return;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(old_val_str, sizeof(old_val_str), data->type, old_val);

pr_err("negation of %s cannot be represented in type %s:\n",
old_val_str, data->type->type_name);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}
EXPORT_SYMBOL(__ubsan_handle_negate_overflow);

@@ -235,13 +229,12 @@ EXPORT_SYMBOL(__ubsan_handle_negate_over
void __ubsan_handle_divrem_overflow(struct overflow_data *data,
void *lhs, void *rhs)
{
- unsigned long flags;
char rhs_val_str[VALUE_LENGTH];

if (suppress_report(&data->location))
return;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(rhs_val_str, sizeof(rhs_val_str), data->type, rhs);

@@ -251,58 +244,52 @@ void __ubsan_handle_divrem_overflow(stru
else
pr_err("division by zero\n");

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}
EXPORT_SYMBOL(__ubsan_handle_divrem_overflow);

static void handle_null_ptr_deref(struct type_mismatch_data_common *data)
{
- unsigned long flags;
-
if (suppress_report(data->location))
return;

- ubsan_prologue(data->location, &flags);
+ ubsan_prologue(data->location);

pr_err("%s null pointer of type %s\n",
type_check_kinds[data->type_check_kind],
data->type->type_name);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}

static void handle_misaligned_access(struct type_mismatch_data_common *data,
unsigned long ptr)
{
- unsigned long flags;
-
if (suppress_report(data->location))
return;

- ubsan_prologue(data->location, &flags);
+ ubsan_prologue(data->location);

pr_err("%s misaligned address %p for type %s\n",
type_check_kinds[data->type_check_kind],
(void *)ptr, data->type->type_name);
pr_err("which requires %ld byte alignment\n", data->alignment);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}

static void handle_object_size_mismatch(struct type_mismatch_data_common *data,
unsigned long ptr)
{
- unsigned long flags;
-
if (suppress_report(data->location))
return;

- ubsan_prologue(data->location, &flags);
+ ubsan_prologue(data->location);
pr_err("%s address %p with insufficient space\n",
type_check_kinds[data->type_check_kind],
(void *) ptr);
pr_err("for an object of type %s\n", data->type->type_name);
- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}

static void ubsan_type_mismatch_common(struct type_mismatch_data_common *data,
@@ -351,25 +338,23 @@ EXPORT_SYMBOL(__ubsan_handle_type_mismat

void __ubsan_handle_out_of_bounds(struct out_of_bounds_data *data, void *index)
{
- unsigned long flags;
char index_str[VALUE_LENGTH];

if (suppress_report(&data->location))
return;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(index_str, sizeof(index_str), data->index_type, index);
pr_err("index %s is out of range for type %s\n", index_str,
data->array_type->type_name);
- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}
EXPORT_SYMBOL(__ubsan_handle_out_of_bounds);

void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
void *lhs, void *rhs)
{
- unsigned long flags;
struct type_descriptor *rhs_type = data->rhs_type;
struct type_descriptor *lhs_type = data->lhs_type;
char rhs_str[VALUE_LENGTH];
@@ -379,7 +364,7 @@ void __ubsan_handle_shift_out_of_bounds(
if (suppress_report(&data->location))
goto out;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs);
val_to_string(lhs_str, sizeof(lhs_str), lhs_type, lhs);
@@ -402,7 +387,7 @@ void __ubsan_handle_shift_out_of_bounds(
lhs_str, rhs_str,
lhs_type->type_name);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
out:
user_access_restore(ua_flags);
}
@@ -411,11 +396,9 @@ EXPORT_SYMBOL(__ubsan_handle_shift_out_o

void __ubsan_handle_builtin_unreachable(struct unreachable_data *data)
{
- unsigned long flags;
-
- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);
pr_err("calling __builtin_unreachable()\n");
- ubsan_epilogue(&flags);
+ ubsan_epilogue();
panic("can't return from __builtin_unreachable()");
}
EXPORT_SYMBOL(__ubsan_handle_builtin_unreachable);
@@ -423,19 +406,18 @@ EXPORT_SYMBOL(__ubsan_handle_builtin_unr
void __ubsan_handle_load_invalid_value(struct invalid_value_data *data,
void *val)
{
- unsigned long flags;
char val_str[VALUE_LENGTH];

if (suppress_report(&data->location))
return;

- ubsan_prologue(&data->location, &flags);
+ ubsan_prologue(&data->location);

val_to_string(val_str, sizeof(val_str), data->type, val);

pr_err("load of value %s is not a valid value for type %s\n",
val_str, data->type->type_name);

- ubsan_epilogue(&flags);
+ ubsan_epilogue();
}
EXPORT_SYMBOL(__ubsan_handle_load_invalid_value);
_