Re: [PATCH net] s390/ism: Zerorize dmb at allocation

[sashiko-bot@kernel.org]

> 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 <wintera@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260928114741.4135978-1-wintera@linux.ibm.com?part=1