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Tue, 29 Sep 2026 17:51:58 -0700 (PDT) Date: Tue, 29 Sep 2026 17:51:56 -0700 From: Joe Damato To: Alexandra Winter Cc: Aswin Karuvally , Gerd Bayer , David Miller , Jakub Kicinski , Paolo Abeni , Eric Dumazet , Andrew Lunn , Julian Ruess , netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Simon Horman Subject: Re: [PATCH net] s390/ism: Zerorize dmb at allocation Message-ID: Mail-Followup-To: Joe Damato , Alexandra Winter , Aswin Karuvally , Gerd Bayer , David Miller , Jakub Kicinski , Paolo Abeni , Eric Dumazet , Andrew Lunn , Julian Ruess , netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Simon Horman References: <20260928114741.4135978-1-wintera@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260928114741.4135978-1-wintera@linux.ibm.com> On Mon, Sep 28, 2026 at 01:47:41PM +0200, Alexandra Winter wrote: > Sashiko reported [1] that 'Missing __GFP_ZERO in folio_alloc() causes > uninitialized kernel memory to be exposed in the receive message buffer'. > An ism dmb is receive-only, so the data is not leaked to a remote peer. In > general the smc kernel module (dibs client) will only push newly received > data to userspace. We still should not have uninitialized data in a receive > buffer. > > Since > commit 750afb08ca71 ("cross-tree: phase out dma_zalloc_coherent()") > dma_alloc_coherent no longer required the __GFP_ZERO flag, but when > commit 83781384a96b ("s390/ism: Properly fix receive message buffer allocation") > switched to folio_alloc(), it should have added back the __GFP_ZERO flag. > > Add __GFP_ZERO flag and state in dibs.h that register_dbm() provides > a zerorized buffer (dibs_lo already does). > > Link: https://lore.kernel.org/linux-s390/20260903143746.A5CC41F00A3A@smtp.kernel.org/ [1] > Fixes: 83781384a96b ("s390/ism: Properly fix receive message buffer allocation") > Signed-off-by: Alexandra Winter > Reviewed-by: Julian Ruess > --- > drivers/s390/net/ism_drv.c | 3 ++- > include/linux/dibs.h | 6 +++--- > 2 files changed, 5 insertions(+), 4 deletions(-) Reviewed-by: Joe Damato