In do_page_fault() of ARC we have:
...
fault = handle_mm_fault(vma, address, flags);
/* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
if (unlikely(fatal_signal_pending(current))) {
if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
up_read(&mm->mmap_sem); <---------------- [1]
if (user_mode(regs))
return;
}
...
if (likely(!(fault & VM_FAULT_ERROR))) {
...
return;
}
if (fault & VM_FAULT_OOM)
goto out_of_memory; <----------------- [2]
else if (fault & VM_FAULT_SIGSEGV)
goto bad_area; <----------------- [3]
else if (fault & VM_FAULT_SIGBUS)
goto do_sigbus; <----------------- [4]
Logically it's possible that we might try to release the mmap_sem twice
by having a scenario like:
- task received SIGKILL,
- task handled kernel mode page fault,
- handle_mm_fault() returned with one of VM_FAULT_ERROR,
Then we'll go into path [1] to release the mmap_sem, however we won't
return immediately since user_mode(regs) check will fail (a kernel page
fault). Then we might go into either [2]-[4] and either of them will
try to release the mmap_sem again.
To fix this, we only release the mmap_sem at [1] when we're sure we'll
quit immediately (after we checked with user_mode(regs)).
CC: Vineet Gupta <[email protected]>
CC: "Eric W. Biederman" <[email protected]>
CC: Peter Xu <[email protected]>
CC: Andrew Morton <[email protected]>
CC: Souptick Joarder <[email protected]>
CC: Andrea Arcangeli <[email protected]>
CC: [email protected]
CC: [email protected]
Signed-off-by: Peter Xu <[email protected]>
---
I noticed this only by reading the code. Neither have I verified the
issue, nor have I tested the patch since I even don't know how to (I'm
totally unfamiliar with the arc architecture). However I'm posting this
out first to see whether there's any quick feedback, and in case it's a
valid issue that we've ignored.
---
arch/arc/mm/fault.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index c9da6102eb4f..2d28c3dad5c1 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -142,11 +142,10 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
fault = handle_mm_fault(vma, address, flags);
/* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
- if (unlikely(fatal_signal_pending(current))) {
- if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
+ if (unlikely(fatal_signal_pending(current) && user_mode(regs))) {
+ if (!(fault & VM_FAULT_RETRY))
up_read(&mm->mmap_sem);
- if (user_mode(regs))
- return;
+ return;
}
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
--
2.17.1
On 10/31/18 8:24 PM, Peter Xu wrote:
> In do_page_fault() of ARC we have:
>
> ...
> fault = handle_mm_fault(vma, address, flags);
>
> /* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
> if (unlikely(fatal_signal_pending(current))) {
> if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
> up_read(&mm->mmap_sem); <---------------- [1]
> if (user_mode(regs))
> return;
> }
> ...
> if (likely(!(fault & VM_FAULT_ERROR))) {
> ...
> return;
> }
>
> if (fault & VM_FAULT_OOM)
> goto out_of_memory; <----------------- [2]
> else if (fault & VM_FAULT_SIGSEGV)
> goto bad_area; <----------------- [3]
> else if (fault & VM_FAULT_SIGBUS)
> goto do_sigbus; <----------------- [4]
>
> Logically it's possible that we might try to release the mmap_sem twice
> by having a scenario like:
>
> - task received SIGKILL,
> - task handled kernel mode page fault,
> - handle_mm_fault() returned with one of VM_FAULT_ERROR,
>
> Then we'll go into path [1] to release the mmap_sem, however we won't
> return immediately since user_mode(regs) check will fail (a kernel page
> fault). Then we might go into either [2]-[4] and either of them will
> try to release the mmap_sem again.
>
> To fix this, we only release the mmap_sem at [1] when we're sure we'll
> quit immediately (after we checked with user_mode(regs)).
Hmm, do_page_fault() needs a serious makeover. There's a known problem in the area
you touched (with test case) where we fail to relinquish the mmap_sem for which
Alexey had provided a fix. But I'm going to redo this part now and CC you folks
for review. OK ?
>
> CC: Vineet Gupta <[email protected]>
> CC: "Eric W. Biederman" <[email protected]>
> CC: Peter Xu <[email protected]>
> CC: Andrew Morton <[email protected]>
> CC: Souptick Joarder <[email protected]>
> CC: Andrea Arcangeli <[email protected]>
> CC: [email protected]
> CC: [email protected]
> Signed-off-by: Peter Xu <[email protected]>
> ---
>
> I noticed this only by reading the code. Neither have I verified the
> issue, nor have I tested the patch since I even don't know how to (I'm
> totally unfamiliar with the arc architecture). However I'm posting this
> out first to see whether there's any quick feedback, and in case it's a
> valid issue that we've ignored.
> ---
> arch/arc/mm/fault.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
> index c9da6102eb4f..2d28c3dad5c1 100644
> --- a/arch/arc/mm/fault.c
> +++ b/arch/arc/mm/fault.c
> @@ -142,11 +142,10 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
> fault = handle_mm_fault(vma, address, flags);
>
> /* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
> - if (unlikely(fatal_signal_pending(current))) {
> - if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
> + if (unlikely(fatal_signal_pending(current) && user_mode(regs))) {
> + if (!(fault & VM_FAULT_RETRY))
> up_read(&mm->mmap_sem);
> - if (user_mode(regs))
> - return;
> + return;
> }
>
> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
On Tue, Nov 06, 2018 at 12:48:31AM +0000, Vineet Gupta wrote:
> On 10/31/18 8:24 PM, Peter Xu wrote:
> > In do_page_fault() of ARC we have:
> >
> > ...
> > fault = handle_mm_fault(vma, address, flags);
> >
> > /* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
> > if (unlikely(fatal_signal_pending(current))) {
> > if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
> > up_read(&mm->mmap_sem); <---------------- [1]
> > if (user_mode(regs))
> > return;
> > }
> > ...
> > if (likely(!(fault & VM_FAULT_ERROR))) {
> > ...
> > return;
> > }
> >
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory; <----------------- [2]
> > else if (fault & VM_FAULT_SIGSEGV)
> > goto bad_area; <----------------- [3]
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus; <----------------- [4]
> >
> > Logically it's possible that we might try to release the mmap_sem twice
> > by having a scenario like:
> >
> > - task received SIGKILL,
> > - task handled kernel mode page fault,
> > - handle_mm_fault() returned with one of VM_FAULT_ERROR,
> >
> > Then we'll go into path [1] to release the mmap_sem, however we won't
> > return immediately since user_mode(regs) check will fail (a kernel page
> > fault). Then we might go into either [2]-[4] and either of them will
> > try to release the mmap_sem again.
> >
> > To fix this, we only release the mmap_sem at [1] when we're sure we'll
> > quit immediately (after we checked with user_mode(regs)).
>
> Hmm, do_page_fault() needs a serious makeover. There's a known problem in the area
> you touched (with test case) where we fail to relinquish the mmap_sem for which
> Alexey had provided a fix. But I'm going to redo this part now and CC you folks
> for review. OK ?
Fine with me. Thanks,
--
Peter Xu