| Message ID | 20190918154733.24355-1-billodo@redhat.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [v2] xfs: assure zeroed memory buffers for certain kmem allocations | expand |
On Wed, Sep 18, 2019 at 10:47:33AM -0500, Bill O'Donnell wrote: > Guarantee zeroed memory buffers for cases where potential memory > leak to disk can occur. In these cases, kmem_alloc is used and > doesn't zero the buffer, opening the possibility of information > leakage to disk. > > Introduce a xfs_buf_flag, XBF_ZERO, to indicate a request for a zeroed > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > obtain the already zeroed buffer from kernel memory. > > This solution avoids the performance issue that would occur if a > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> > --- > v2: zeroed buffer not required for XBF_READ case. Correct placement > and rename the XBF_ZERO flag. > > fs/xfs/xfs_buf.c | 9 +++++++-- > fs/xfs/xfs_buf.h | 2 ++ > fs/xfs/xfs_trans_buf.c | 2 ++ > 3 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 120ef99d09e8..0d96efff451e 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -345,6 +345,10 @@ xfs_buf_allocate_memory( > unsigned short page_count, i; > xfs_off_t start, end; > int error; > + uint kmflag_mask = 0; > + > + if ((flags & XBF_ZERO) && !(flags & XBF_READ)) The sole caller of xfs_buf_allocate_memory is xfs_buf_get_map. If _get_map is called from the *read_buf* functions, they pass in XBF_READ to ensure buffer contents are read. The other _get_map callers seem to be initializing metadata blocks and do not set XBF_READ. So I wonder, do you even need XBF_ZERO? Or could this be reduced to: if (!(flags & XBF_READ)) km_flag_mask |= KM_ZERO; ? --D > + kmflag_mask |= KM_ZERO; > > /* > * for buffers that are contained within a single page, just allocate > @@ -354,7 +358,8 @@ xfs_buf_allocate_memory( > size = BBTOB(bp->b_length); > if (size < PAGE_SIZE) { > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > + bp->b_addr = kmem_alloc_io(size, align_mask, > + KM_NOFS | kmflag_mask); > if (!bp->b_addr) { > /* low memory - use alloc_page loop instead */ > goto use_alloc_page; > @@ -391,7 +396,7 @@ xfs_buf_allocate_memory( > struct page *page; > uint retries = 0; > retry: > - page = alloc_page(gfp_mask); > + page = alloc_page(gfp_mask | kmflag_mask); > if (unlikely(page == NULL)) { > if (flags & XBF_READ_AHEAD) { > bp->b_page_count = i; > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > index f6ce17d8d848..dccdd653c9dc 100644 > --- a/fs/xfs/xfs_buf.h > +++ b/fs/xfs/xfs_buf.h > @@ -33,6 +33,7 @@ > /* flags used only as arguments to access routines */ > #define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */ > #define XBF_UNMAPPED (1 << 17)/* do not map the buffer */ > +#define XBF_ZERO (1 << 18)/* zeroed buffer required */ > > /* flags used only internally */ > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > @@ -52,6 +53,7 @@ typedef unsigned int xfs_buf_flags_t; > { XBF_WRITE_FAIL, "WRITE_FAIL" }, \ > { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\ > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > + { XBF_ZERO, "KMEM_ZERO" }, \ > { _XBF_PAGES, "PAGES" }, \ > { _XBF_KMEM, "KMEM" }, \ > { _XBF_DELWRI_Q, "DELWRI_Q" } > diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c > index b5b3a78ef31c..087d413c1490 100644 > --- a/fs/xfs/xfs_trans_buf.c > +++ b/fs/xfs/xfs_trans_buf.c > @@ -123,6 +123,8 @@ xfs_trans_get_buf_map( > xfs_buf_t *bp; > struct xfs_buf_log_item *bip; > > + flags |= XBF_ZERO; > + > if (!tp) > return xfs_buf_get_map(target, map, nmaps, flags); > > -- > 2.21.0 >
On Wed, Sep 18, 2019 at 09:32:13AM -0700, Darrick J. Wong wrote: > On Wed, Sep 18, 2019 at 10:47:33AM -0500, Bill O'Donnell wrote: > > Guarantee zeroed memory buffers for cases where potential memory > > leak to disk can occur. In these cases, kmem_alloc is used and > > doesn't zero the buffer, opening the possibility of information > > leakage to disk. > > > > Introduce a xfs_buf_flag, XBF_ZERO, to indicate a request for a zeroed > > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > > obtain the already zeroed buffer from kernel memory. > > > > This solution avoids the performance issue that would occur if a > > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> > > --- > > v2: zeroed buffer not required for XBF_READ case. Correct placement > > and rename the XBF_ZERO flag. > > > > fs/xfs/xfs_buf.c | 9 +++++++-- > > fs/xfs/xfs_buf.h | 2 ++ > > fs/xfs/xfs_trans_buf.c | 2 ++ > > 3 files changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index 120ef99d09e8..0d96efff451e 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -345,6 +345,10 @@ xfs_buf_allocate_memory( > > unsigned short page_count, i; > > xfs_off_t start, end; > > int error; > > + uint kmflag_mask = 0; > > + > > + if ((flags & XBF_ZERO) && !(flags & XBF_READ)) > > The sole caller of xfs_buf_allocate_memory is xfs_buf_get_map. If > _get_map is called from the *read_buf* functions, they pass in XBF_READ > to ensure buffer contents are read. The other _get_map callers seem to > be initializing metadata blocks and do not set XBF_READ. > > So I wonder, do you even need XBF_ZERO? Or could this be reduced to: > > if (!(flags & XBF_READ)) > km_flag_mask |= KM_ZERO; > > ? > > --D Yeah, I see no cases of XBF_ZERO true AND XBF_READ true. Anytime XBF_ZERO is true, XBF_READ is false. So, yes, it could be reduced by eliminating XBF_ZERO. Thanks, Bill > > > + kmflag_mask |= KM_ZERO; > > > > /* > > * for buffers that are contained within a single page, just allocate > > @@ -354,7 +358,8 @@ xfs_buf_allocate_memory( > > size = BBTOB(bp->b_length); > > if (size < PAGE_SIZE) { > > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > > + bp->b_addr = kmem_alloc_io(size, align_mask, > > + KM_NOFS | kmflag_mask); > > if (!bp->b_addr) { > > /* low memory - use alloc_page loop instead */ > > goto use_alloc_page; > > @@ -391,7 +396,7 @@ xfs_buf_allocate_memory( > > struct page *page; > > uint retries = 0; > > retry: > > - page = alloc_page(gfp_mask); > > + page = alloc_page(gfp_mask | kmflag_mask); > > if (unlikely(page == NULL)) { > > if (flags & XBF_READ_AHEAD) { > > bp->b_page_count = i; > > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > > index f6ce17d8d848..dccdd653c9dc 100644 > > --- a/fs/xfs/xfs_buf.h > > +++ b/fs/xfs/xfs_buf.h > > @@ -33,6 +33,7 @@ > > /* flags used only as arguments to access routines */ > > #define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */ > > #define XBF_UNMAPPED (1 << 17)/* do not map the buffer */ > > +#define XBF_ZERO (1 << 18)/* zeroed buffer required */ > > > > /* flags used only internally */ > > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > > @@ -52,6 +53,7 @@ typedef unsigned int xfs_buf_flags_t; > > { XBF_WRITE_FAIL, "WRITE_FAIL" }, \ > > { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\ > > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > > + { XBF_ZERO, "KMEM_ZERO" }, \ > > { _XBF_PAGES, "PAGES" }, \ > > { _XBF_KMEM, "KMEM" }, \ > > { _XBF_DELWRI_Q, "DELWRI_Q" } > > diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c > > index b5b3a78ef31c..087d413c1490 100644 > > --- a/fs/xfs/xfs_trans_buf.c > > +++ b/fs/xfs/xfs_trans_buf.c > > @@ -123,6 +123,8 @@ xfs_trans_get_buf_map( > > xfs_buf_t *bp; > > struct xfs_buf_log_item *bip; > > > > + flags |= XBF_ZERO; > > + > > if (!tp) > > return xfs_buf_get_map(target, map, nmaps, flags); > > > > -- > > 2.21.0 > >
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 120ef99d09e8..0d96efff451e 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -345,6 +345,10 @@ xfs_buf_allocate_memory( unsigned short page_count, i; xfs_off_t start, end; int error; + uint kmflag_mask = 0; + + if ((flags & XBF_ZERO) && !(flags & XBF_READ)) + kmflag_mask |= KM_ZERO; /* * for buffers that are contained within a single page, just allocate @@ -354,7 +358,8 @@ xfs_buf_allocate_memory( size = BBTOB(bp->b_length); if (size < PAGE_SIZE) { int align_mask = xfs_buftarg_dma_alignment(bp->b_target); - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); + bp->b_addr = kmem_alloc_io(size, align_mask, + KM_NOFS | kmflag_mask); if (!bp->b_addr) { /* low memory - use alloc_page loop instead */ goto use_alloc_page; @@ -391,7 +396,7 @@ xfs_buf_allocate_memory( struct page *page; uint retries = 0; retry: - page = alloc_page(gfp_mask); + page = alloc_page(gfp_mask | kmflag_mask); if (unlikely(page == NULL)) { if (flags & XBF_READ_AHEAD) { bp->b_page_count = i; diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h index f6ce17d8d848..dccdd653c9dc 100644 --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h @@ -33,6 +33,7 @@ /* flags used only as arguments to access routines */ #define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */ #define XBF_UNMAPPED (1 << 17)/* do not map the buffer */ +#define XBF_ZERO (1 << 18)/* zeroed buffer required */ /* flags used only internally */ #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ @@ -52,6 +53,7 @@ typedef unsigned int xfs_buf_flags_t; { XBF_WRITE_FAIL, "WRITE_FAIL" }, \ { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\ { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ + { XBF_ZERO, "KMEM_ZERO" }, \ { _XBF_PAGES, "PAGES" }, \ { _XBF_KMEM, "KMEM" }, \ { _XBF_DELWRI_Q, "DELWRI_Q" } diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c index b5b3a78ef31c..087d413c1490 100644 --- a/fs/xfs/xfs_trans_buf.c +++ b/fs/xfs/xfs_trans_buf.c @@ -123,6 +123,8 @@ xfs_trans_get_buf_map( xfs_buf_t *bp; struct xfs_buf_log_item *bip; + flags |= XBF_ZERO; + if (!tp) return xfs_buf_get_map(target, map, nmaps, flags);
Guarantee zeroed memory buffers for cases where potential memory leak to disk can occur. In these cases, kmem_alloc is used and doesn't zero the buffer, opening the possibility of information leakage to disk. Introduce a xfs_buf_flag, XBF_ZERO, to indicate a request for a zeroed buffer, and use existing infrastucture (xfs_buf_allocate_memory) to obtain the already zeroed buffer from kernel memory. This solution avoids the performance issue that would occur if a wholesale change to replace kmem_alloc with kmem_zalloc was done. Signed-off-by: Bill O'Donnell <billodo@redhat.com> --- v2: zeroed buffer not required for XBF_READ case. Correct placement and rename the XBF_ZERO flag. fs/xfs/xfs_buf.c | 9 +++++++-- fs/xfs/xfs_buf.h | 2 ++ fs/xfs/xfs_trans_buf.c | 2 ++ 3 files changed, 11 insertions(+), 2 deletions(-)