On Wed, Jun 13, 2018 at 10:58:37AM +0200, Marek Szyprowski wrote: > cma_alloc() function has gfp mask parameter, so users expect that it > honors typical memory allocation related flags. The most imporant from > the security point of view is handling of __GFP_ZERO flag, because memory > allocated by this function usually can be directly remapped to userspace > by device drivers as a part of multimedia processing and ignoring this > flag might lead to leaking some kernel structures to userspace. > Some callers of this function (for example arm64 dma-iommu glue code) > already assumed that the allocated buffers are cleared when this flag > is set. To avoid such issues, add simple code for clearing newly > allocated buffer when __GFP_ZERO flag is set. Callers will be then > updated to skip implicit clearing or adjust passed gfp flags. I think the documentation for this function needs improving. For example, GFP_ATOMIC does not work (it takes a mutex lock, so it can sleep). At the very least, the kernel-doc needs: * Context: Process context (may sleep even if GFP flags indicate otherwise). Unless someone wants to rework this allocator to use spinlocks instead of mutexes ...
