[patch 068/262] mm/mmap.c: fix a data race of mm->total_vm

Andrew Morton
2021-11-05T20:38:15Z

From: Peng Liu <liupeng256@huawei.com>
Subject: mm/mmap.c: fix a data race of mm->total_vm

Variable mm->total_vm could be accessed concurrently during mmaping and
system accounting as noticed by KCSAN,

BUG: KCSAN: data-race in __acct_update_integrals / mmap_region

read-write to 0xffffa40267bd14c8 of 8 bytes by task 15609 on cpu 3:
mmap_region+0x6dc/0x1400
do_mmap+0x794/0xca0
vm_mmap_pgoff+0xdf/0x150
ksys_mmap_pgoff+0xe1/0x380
do_syscall_64+0x37/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffa40267bd14c8 of 8 bytes by interrupt on cpu 2:
__acct_update_integrals+0x187/0x1d0
acct_account_cputime+0x3c/0x40
update_process_times+0x5c/0x150
tick_sched_timer+0x184/0x210
__run_hrtimer+0x119/0x3b0
hrtimer_interrupt+0x350/0xaa0
__sysvec_apic_timer_interrupt+0x7b/0x220
asm_call_irq_on_stack+0x12/0x20
sysvec_apic_timer_interrupt+0x4d/0x80
asm_sysvec_apic_timer_interrupt+0x12/0x20
smp_call_function_single+0x192/0x2b0
perf_install_in_context+0x29b/0x4a0
__se_sys_perf_event_open+0x1a98/0x2550
__x64_sys_perf_event_open+0x63/0x70
do_syscall_64+0x37/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 2 PID: 15610 Comm: syz-executor.3 Not tainted 5.10.0+ #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
Ubuntu-1.8.2-1ubuntu1 04/01/2014

In vm_stat_account which called by mmap_region, increase total_vm, and
__acct_update_integrals may read total_vm at the same time. This will
cause a data race which lead to undefined behaviour. To avoid potential
bad read/write, volatile property and barrier are both used to avoid
undefined behaviour.

Link: https://lkml.kernel.org/r/20210913105550.1569419-1-liupeng256@huawei.com
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

kernel/tsacct.c | 2 +-
mm/mmap.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/tsacct.c~mm-mmapc-fix-a-data-race-of-mm-total_vm
+++ a/kernel/tsacct.c
@@ -137,7 +137,7 @@ static void __acct_update_integrals(stru
* the rest of the math is done in xacct_add_tsk.
*/
tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm) >> 10;
- tsk->acct_vm_mem1 += delta * tsk->mm->total_vm >> 10;
+ tsk->acct_vm_mem1 += delta * READ_ONCE(tsk->mm->total_vm) >> 10;
}

/**
--- a/mm/mmap.c~mm-mmapc-fix-a-data-race-of-mm-total_vm
+++ a/mm/mmap.c
@@ -3332,7 +3332,7 @@ bool may_expand_vm(struct mm_struct *mm,

void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
{
- mm->total_vm += npages;
+ WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm)+npages);

if (is_exec_mapping(flags))
mm->exec_vm += npages;
_