| Message ID | 20210921200247.25749-1-namit@vmware.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | userfaultfd: fix a race between writeprotect and exit_mmap() | expand |
Hi, I confirmed this patch (applied on 5.14) gets rid of the below userfaultfd test failure. # ./userfaultfd anon 16 2 nr_pages: 4096, nr_pages_per_cpu: 256 bounces: 1, mode: rnd read, userfaults: 313 missing (51+34+37+26+41+28+15+20+16+12+13+7+10+2+0+1) 995 wp (121+79+96+53+90+104+48+61+56+82+56+41+49+26+11+22) bounces: 0, mode: read, userfaults: 64 missing (15+8+10+6+5+2+4+3+3+1+4+0+0+2+0+1) 2157 wp (223+274+189+141+116+132+203+153+143+126+110+114+101+66+42+24) testing uffd-wp with pagemap (pgsize=4096): done testing uffd-wp with pagemap (pgsize=2097152): done testing UFFDIO_ZEROPAGE: done. testing signal delivery: done. testing events (fork, remap, remove): ERROR: nr 3933 memory corruption 0 1 (errno=0, line=963) ERROR: faulting process failed (errno=0, line=1117) On Wed, Sep 22, 2021 at 11:34 AM Nadav Amit <nadav.amit@gmail.com> wrote: > From: Nadav Amit <namit@vmware.com> > > A race is possible when a process exits, its VMAs are removed > by exit_mmap() and at the same time userfaultfd_writeprotect() is > called. > > The race was detected by KASAN on a development kernel, but it appears > to be possible on vanilla kernels as well. > > Use mmget_not_zero() to prevent the race as done in other userfaultfd > operations. > > Cc: Peter Xu <peterx@redhat.com> > Cc: Andrea Arcangeli <aarcange@redhat.com> > Cc: stable@vger.kernel.org > Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to > userfaultfd ioctl") > Signed-off-by: Nadav Amit <namit@vmware.com> > Tested-by: Li Wang <liwang@redhat.com> > --- > fs/userfaultfd.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 003f0d31743e..22bf14ab2d16 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1827,9 +1827,15 @@ static int userfaultfd_writeprotect(struct > userfaultfd_ctx *ctx, > if (mode_wp && mode_dontwake) > return -EINVAL; > > - ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, > - uffdio_wp.range.len, mode_wp, > - &ctx->mmap_changing); > + if (mmget_not_zero(ctx->mm)) { > + ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, > + uffdio_wp.range.len, mode_wp, > + &ctx->mmap_changing); > + mmput(ctx->mm); > + } else { > + return -ESRCH; > + } > + > if (ret) > return ret; > > -- > 2.25.1 > > >
On Tue, Sep 21, 2021 at 01:02:47PM -0700, Nadav Amit wrote: > From: Nadav Amit <namit@vmware.com> > > A race is possible when a process exits, its VMAs are removed > by exit_mmap() and at the same time userfaultfd_writeprotect() is > called. > > The race was detected by KASAN on a development kernel, but it appears > to be possible on vanilla kernels as well. > > Use mmget_not_zero() to prevent the race as done in other userfaultfd > operations. > > Cc: Peter Xu <peterx@redhat.com> > Cc: Andrea Arcangeli <aarcange@redhat.com> > Cc: stable@vger.kernel.org > Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") > Signed-off-by: Nadav Amit <namit@vmware.com> Reviewed-by: Peter Xu <peterx@redhat.com> Thanks!
On Wed, Sep 22, 2021 at 05:06:53PM +0800, Li Wang wrote: > Hi, Li, > > I confirmed this patch (applied on 5.14) gets rid of the below userfaultfd > test failure. > > # ./userfaultfd anon 16 2 > nr_pages: 4096, nr_pages_per_cpu: 256 > bounces: 1, mode: rnd read, userfaults: 313 missing > (51+34+37+26+41+28+15+20+16+12+13+7+10+2+0+1) 995 wp > (121+79+96+53+90+104+48+61+56+82+56+41+49+26+11+22) > bounces: 0, mode: read, userfaults: 64 missing > (15+8+10+6+5+2+4+3+3+1+4+0+0+2+0+1) 2157 wp > (223+274+189+141+116+132+203+153+143+126+110+114+101+66+42+24) > testing uffd-wp with pagemap (pgsize=4096): done > testing uffd-wp with pagemap (pgsize=2097152): done > testing UFFDIO_ZEROPAGE: done. > testing signal delivery: done. > testing events (fork, remap, remove): ERROR: nr 3933 memory corruption 0 1 > (errno=0, line=963) > ERROR: faulting process failed (errno=0, line=1117) Just to keep a record within this thread - my understanding is above issue is a separate issue from what Nadav has fixed. The other fix could be: https://lore.kernel.org/lkml/20210923232512.210092-1-peterx@redhat.com/ When verify with Nadav's patch, please check whether you have thp enabled globally: # echo always > /sys/kernel/mm/transparent_hugepage/enabled Thanks,
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 003f0d31743e..22bf14ab2d16 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1827,9 +1827,15 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, if (mode_wp && mode_dontwake) return -EINVAL; - ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, - uffdio_wp.range.len, mode_wp, - &ctx->mmap_changing); + if (mmget_not_zero(ctx->mm)) { + ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, + uffdio_wp.range.len, mode_wp, + &ctx->mmap_changing); + mmput(ctx->mm); + } else { + return -ESRCH; + } + if (ret) return ret;