| Message ID | 20220408030137.3693195-1-npache@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v7] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head | expand |
On Thu, 7 Apr 2022 23:01:37 -0400 Nico Pache <npache@redhat.com> wrote: > The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which can > be targeted by the oom reaper. This mapping is used to store the futex > robust list head; the kernel does not keep a copy of the robust list and > instead references a userspace address to maintain the robustness during > a process death. A race can occur between exit_mm and the oom reaper that > allows the oom reaper to free the memory of the futex robust list before > the exit path has handled the futex death: > > CPU1 CPU2 > ------------------------------------------------------------------------ > page_fault > do_exit "signal" > wake_oom_reaper > oom_reaper > oom_reap_task_mm (invalidates mm) > exit_mm > exit_mm_release > futex_exit_release > futex_cleanup > exit_robust_list > get_user (EFAULT- can't access memory) > > If the get_user EFAULT's, the kernel will be unable to recover the > waiters on the robust_list, leaving userspace mutexes hung indefinitely. > > Use the robust_list address stored in the kernel to skip the VMA that holds > it, allowing a successful futex_cleanup. > > Theoretically a failure can still occur if there are locks mapped as > PRIVATE|ANON; however, the robust futexes are a best-effort approach. > This patch only strengthens that best-effort. > > The following case can still fail: > robust head (skipped) -> private lock (reaped) -> shared lock (skipped) > > Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer > > [1] https://elixir.bootlin.com/glibc/latest/source/nptl/allocatestack.c#L370 > > ... > > --- a/include/linux/oom.h > +++ b/include/linux/oom.h > @@ -106,7 +106,7 @@ static inline vm_fault_t check_stable_address_space(struct mm_struct *mm) > return 0; > } > > -bool __oom_reap_task_mm(struct mm_struct *mm); > +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list); > > long oom_badness(struct task_struct *p, > unsigned long totalpages); > diff --git a/mm/mmap.c b/mm/mmap.c > index 3aa839f81e63..d5af1b83cbb2 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3109,6 +3109,11 @@ void exit_mmap(struct mm_struct *mm) > struct mmu_gather tlb; > struct vm_area_struct *vma; > unsigned long nr_accounted = 0; > + void *robust_list; > + > +#ifdef CONFIG_FUTEX > + robust_list = current->robust_list; > +#endif > > /* mm's last user has gone, and its about to be pulled down */ > mmu_notifier_release(mm); > @@ -3126,7 +3131,8 @@ void exit_mmap(struct mm_struct *mm) > * to mmu_notifier_release(mm) ensures mmu notifier callbacks in > * __oom_reap_task_mm() will not block. > */ > - (void)__oom_reap_task_mm(mm); > + (void)__oom_reap_task_mm(mm, robust_list); uninitialized var warning when CONFIG_FUTEX=n? > + > set_bit(MMF_OOM_SKIP, &mm->flags); > } > > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -509,9 +509,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait); > static struct task_struct *oom_reaper_list; > static DEFINE_SPINLOCK(oom_reaper_lock); > > -bool __oom_reap_task_mm(struct mm_struct *mm) > +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list) Well, this is no longer necessarily a robust_list*. It's just an address to skip and the name should reflect that? > { > struct vm_area_struct *vma; > + unsigned long skip_vma = (unsigned long) robust_list; > bool ret = true; > > /* > @@ -526,6 +527,20 @@ bool __oom_reap_task_mm(struct mm_struct *mm) > if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP)) > continue; > > +#ifdef CONFIG_FUTEX > + /* > + * The OOM reaper runs concurrently with do_exit. > + * The robust_list_head is stored in userspace and is required > + * by the exit path to recover the robust futex waiters. > + * Skip the VMA that contains the robust_list to allow for > + * proper cleanup. > + */ > + if (vma->vm_start <= skip_vma && vma->vm_end > skip_vma) { > + pr_info("oom_reaper: skipping vma, contains robust_list"); > + continue; > + } > +#endif > + > /* > * Only anonymous pages have a good chance to be dropped > * without additional steps which we cannot afford as we > @@ -567,6 +582,7 @@ bool __oom_reap_task_mm(struct mm_struct *mm) > static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) > { > bool ret = true; > + void *robust_list; > > if (!mmap_read_trylock(mm)) { > trace_skip_task_reaping(tsk->pid); > @@ -586,8 +602,11 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) > > trace_start_task_reaping(tsk->pid); > > +#ifdef CONFIG_FUTEX > + robust_list = tsk->robust_list; > +#endif > /* failed to reap part of the address space. Try again later */ > - ret = __oom_reap_task_mm(mm); > + ret = __oom_reap_task_mm(mm, robust_list); unintialized var when CONFIG_FUTEX=n? > if (!ret) > goto out_finish; > > @@ -1149,6 +1168,7 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) > unsigned int f_flags; > bool reap = false; > long ret = 0; > + void *robust_list; > > if (flags) > return -EINVAL; > @@ -1186,11 +1206,16 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) > ret = -EINTR; > goto drop_mm; > } > + > +#ifdef CONFIG_FUTEX > + robust_list = p->robust_list; > +#endif > /* > * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure > * possible change in exit_mmap is seen > */ > - if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm)) > + if (!test_bit(MMF_OOM_SKIP, &mm->flags) && > + !__oom_reap_task_mm(mm, robust_list)) again > ret = -EAGAIN; > mmap_read_unlock(mm);
On 4/7/22 23:12, Andrew Morton wrote: > On Thu, 7 Apr 2022 23:01:37 -0400 Nico Pache <npache@redhat.com> wrote: > >> The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which can >> be targeted by the oom reaper. This mapping is used to store the futex >> robust list head; the kernel does not keep a copy of the robust list and >> instead references a userspace address to maintain the robustness during >> a process death. A race can occur between exit_mm and the oom reaper that >> allows the oom reaper to free the memory of the futex robust list before >> the exit path has handled the futex death: >> >> CPU1 CPU2 >> ------------------------------------------------------------------------ >> page_fault >> do_exit "signal" >> wake_oom_reaper >> oom_reaper >> oom_reap_task_mm (invalidates mm) >> exit_mm >> exit_mm_release >> futex_exit_release >> futex_cleanup >> exit_robust_list >> get_user (EFAULT- can't access memory) >> >> If the get_user EFAULT's, the kernel will be unable to recover the >> waiters on the robust_list, leaving userspace mutexes hung indefinitely. >> >> Use the robust_list address stored in the kernel to skip the VMA that holds >> it, allowing a successful futex_cleanup. >> >> Theoretically a failure can still occur if there are locks mapped as >> PRIVATE|ANON; however, the robust futexes are a best-effort approach. >> This patch only strengthens that best-effort. >> >> The following case can still fail: >> robust head (skipped) -> private lock (reaped) -> shared lock (skipped) >> >> Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer >> >> [1] https://elixir.bootlin.com/glibc/latest/source/nptl/allocatestack.c#L370 >> >> ... >> >> --- a/include/linux/oom.h >> +++ b/include/linux/oom.h >> @@ -106,7 +106,7 @@ static inline vm_fault_t check_stable_address_space(struct mm_struct *mm) >> return 0; >> } >> >> -bool __oom_reap_task_mm(struct mm_struct *mm); >> +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list); >> >> long oom_badness(struct task_struct *p, >> unsigned long totalpages); >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 3aa839f81e63..d5af1b83cbb2 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -3109,6 +3109,11 @@ void exit_mmap(struct mm_struct *mm) >> struct mmu_gather tlb; >> struct vm_area_struct *vma; >> unsigned long nr_accounted = 0; >> + void *robust_list; >> + >> +#ifdef CONFIG_FUTEX >> + robust_list = current->robust_list; >> +#endif >> >> /* mm's last user has gone, and its about to be pulled down */ >> mmu_notifier_release(mm); >> @@ -3126,7 +3131,8 @@ void exit_mmap(struct mm_struct *mm) >> * to mmu_notifier_release(mm) ensures mmu notifier callbacks in >> * __oom_reap_task_mm() will not block. >> */ >> - (void)__oom_reap_task_mm(mm); >> + (void)__oom_reap_task_mm(mm, robust_list); > > uninitialized var warning when CONFIG_FUTEX=n? > >> + >> set_bit(MMF_OOM_SKIP, &mm->flags); >> } >> >> --- a/mm/oom_kill.c >> +++ b/mm/oom_kill.c >> @@ -509,9 +509,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait); >> static struct task_struct *oom_reaper_list; >> static DEFINE_SPINLOCK(oom_reaper_lock); >> >> -bool __oom_reap_task_mm(struct mm_struct *mm) >> +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list) > > Well, this is no longer necessarily a robust_list*. It's just an > address to skip and the name should reflect that? ok fair point. I left it as robust list to be more clean what is being skipped and renamed the head variable to skip_vma so its more verbose. But I dont have that strong of an opinion on it so I'll change it real quick. > >> { >> struct vm_area_struct *vma; >> + unsigned long skip_vma = (unsigned long) robust_list; >> bool ret = true; >> >> /* >> @@ -526,6 +527,20 @@ bool __oom_reap_task_mm(struct mm_struct *mm) >> if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP)) >> continue; >> >> +#ifdef CONFIG_FUTEX >> + /* >> + * The OOM reaper runs concurrently with do_exit. >> + * The robust_list_head is stored in userspace and is required >> + * by the exit path to recover the robust futex waiters. >> + * Skip the VMA that contains the robust_list to allow for >> + * proper cleanup. >> + */ >> + if (vma->vm_start <= skip_vma && vma->vm_end > skip_vma) { >> + pr_info("oom_reaper: skipping vma, contains robust_list"); >> + continue; >> + } >> +#endif >> + >> /* >> * Only anonymous pages have a good chance to be dropped >> * without additional steps which we cannot afford as we >> @@ -567,6 +582,7 @@ bool __oom_reap_task_mm(struct mm_struct *mm) >> static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) >> { >> bool ret = true; >> + void *robust_list; >> >> if (!mmap_read_trylock(mm)) { >> trace_skip_task_reaping(tsk->pid); >> @@ -586,8 +602,11 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) >> >> trace_start_task_reaping(tsk->pid); >> >> +#ifdef CONFIG_FUTEX >> + robust_list = tsk->robust_list; >> +#endif >> /* failed to reap part of the address space. Try again later */ >> - ret = __oom_reap_task_mm(mm); >> + ret = __oom_reap_task_mm(mm, robust_list); > > unintialized var when CONFIG_FUTEX=n? > >> if (!ret) >> goto out_finish; >> >> @@ -1149,6 +1168,7 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) >> unsigned int f_flags; >> bool reap = false; >> long ret = 0; >> + void *robust_list; >> >> if (flags) >> return -EINVAL; >> @@ -1186,11 +1206,16 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) >> ret = -EINTR; >> goto drop_mm; >> } >> + >> +#ifdef CONFIG_FUTEX >> + robust_list = p->robust_list; >> +#endif >> /* >> * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure >> * possible change in exit_mmap is seen >> */ >> - if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm)) >> + if (!test_bit(MMF_OOM_SKIP, &mm->flags) && >> + !__oom_reap_task_mm(mm, robust_list)) > > again Good catch. Ill fix those real quick. > >> ret = -EAGAIN; >> mmap_read_unlock(mm); >
diff --git a/include/linux/oom.h b/include/linux/oom.h index 2db9a1432511..5253fcee049e 100644 --- a/include/linux/oom.h +++ b/include/linux/oom.h @@ -106,7 +106,7 @@ static inline vm_fault_t check_stable_address_space(struct mm_struct *mm) return 0; } -bool __oom_reap_task_mm(struct mm_struct *mm); +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list); long oom_badness(struct task_struct *p, unsigned long totalpages); diff --git a/mm/mmap.c b/mm/mmap.c index 3aa839f81e63..d5af1b83cbb2 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3109,6 +3109,11 @@ void exit_mmap(struct mm_struct *mm) struct mmu_gather tlb; struct vm_area_struct *vma; unsigned long nr_accounted = 0; + void *robust_list; + +#ifdef CONFIG_FUTEX + robust_list = current->robust_list; +#endif /* mm's last user has gone, and its about to be pulled down */ mmu_notifier_release(mm); @@ -3126,7 +3131,8 @@ void exit_mmap(struct mm_struct *mm) * to mmu_notifier_release(mm) ensures mmu notifier callbacks in * __oom_reap_task_mm() will not block. */ - (void)__oom_reap_task_mm(mm); + (void)__oom_reap_task_mm(mm, robust_list); + set_bit(MMF_OOM_SKIP, &mm->flags); } diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 7ec38194f8e1..f856d8dd53e1 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -509,9 +509,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait); static struct task_struct *oom_reaper_list; static DEFINE_SPINLOCK(oom_reaper_lock); -bool __oom_reap_task_mm(struct mm_struct *mm) +bool __oom_reap_task_mm(struct mm_struct *mm, void *robust_list) { struct vm_area_struct *vma; + unsigned long skip_vma = (unsigned long) robust_list; bool ret = true; /* @@ -526,6 +527,20 @@ bool __oom_reap_task_mm(struct mm_struct *mm) if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP)) continue; +#ifdef CONFIG_FUTEX + /* + * The OOM reaper runs concurrently with do_exit. + * The robust_list_head is stored in userspace and is required + * by the exit path to recover the robust futex waiters. + * Skip the VMA that contains the robust_list to allow for + * proper cleanup. + */ + if (vma->vm_start <= skip_vma && vma->vm_end > skip_vma) { + pr_info("oom_reaper: skipping vma, contains robust_list"); + continue; + } +#endif + /* * Only anonymous pages have a good chance to be dropped * without additional steps which we cannot afford as we @@ -567,6 +582,7 @@ bool __oom_reap_task_mm(struct mm_struct *mm) static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) { bool ret = true; + void *robust_list; if (!mmap_read_trylock(mm)) { trace_skip_task_reaping(tsk->pid); @@ -586,8 +602,11 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) trace_start_task_reaping(tsk->pid); +#ifdef CONFIG_FUTEX + robust_list = tsk->robust_list; +#endif /* failed to reap part of the address space. Try again later */ - ret = __oom_reap_task_mm(mm); + ret = __oom_reap_task_mm(mm, robust_list); if (!ret) goto out_finish; @@ -1149,6 +1168,7 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) unsigned int f_flags; bool reap = false; long ret = 0; + void *robust_list; if (flags) return -EINVAL; @@ -1186,11 +1206,16 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) ret = -EINTR; goto drop_mm; } + +#ifdef CONFIG_FUTEX + robust_list = p->robust_list; +#endif /* * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure * possible change in exit_mmap is seen */ - if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm)) + if (!test_bit(MMF_OOM_SKIP, &mm->flags) && + !__oom_reap_task_mm(mm, robust_list)) ret = -EAGAIN; mmap_read_unlock(mm);
The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which can be targeted by the oom reaper. This mapping is used to store the futex robust list head; the kernel does not keep a copy of the robust list and instead references a userspace address to maintain the robustness during a process death. A race can occur between exit_mm and the oom reaper that allows the oom reaper to free the memory of the futex robust list before the exit path has handled the futex death: CPU1 CPU2 ------------------------------------------------------------------------ page_fault do_exit "signal" wake_oom_reaper oom_reaper oom_reap_task_mm (invalidates mm) exit_mm exit_mm_release futex_exit_release futex_cleanup exit_robust_list get_user (EFAULT- can't access memory) If the get_user EFAULT's, the kernel will be unable to recover the waiters on the robust_list, leaving userspace mutexes hung indefinitely. Use the robust_list address stored in the kernel to skip the VMA that holds it, allowing a successful futex_cleanup. Theoretically a failure can still occur if there are locks mapped as PRIVATE|ANON; however, the robust futexes are a best-effort approach. This patch only strengthens that best-effort. The following case can still fail: robust head (skipped) -> private lock (reaped) -> shared lock (skipped) Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer [1] https://elixir.bootlin.com/glibc/latest/source/nptl/allocatestack.c#L370 Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently") Cc: Rafael Aquini <aquini@redhat.com> Cc: Waiman Long <longman@redhat.com> Cc: Baoquan He <bhe@redhat.com> Cc: Christoph von Recklinghausen <crecklin@redhat.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Herton R. Krzesinski <herton@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Joel Savitz <jsavitz@redhat.com> Cc: Darren Hart <dvhart@infradead.org> Cc: stable@kernel.org Co-developed-by: Joel Savitz <jsavitz@redhat.com> Signed-off-by: Joel Savitz <jsavitz@redhat.com> Signed-off-by: Nico Pache <npache@redhat.com> --- include/linux/oom.h | 2 +- mm/mmap.c | 8 +++++++- mm/oom_kill.c | 31 ++++++++++++++++++++++++++++--- 3 files changed, 36 insertions(+), 5 deletions(-)