Hi Matthew, On 2018-06-13 14:24, Matthew Wilcox wrote: > 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 ...
It is not only the matter of the spinlocks. GFP_ATOMIC is not supported by the memory compaction code, which is used in alloc_contig_range(). Right, this should be also noted in the documentation. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
