Messages in this thread | | | Subject | Re: [PATCH] dma-mapping: Lift address space checks out of debug code | From | Robin Murphy <> | Date | Wed, 2 Oct 2019 22:15:43 +0100 |
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Hi Kees,
On 2019-10-02 9:46 pm, Kees Cook wrote: > As we've seen from USB and other areas, we need to always do runtime > checks for DMA operating on memory regions that might be remapped. This > consolidates the (existing!) checks and makes them on by default. A > warning will be triggered for any drivers still using DMA on the stack > (as has been seen in a few recent reports). > > Suggested-by: Laura Abbott <labbott@redhat.com> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > include/linux/dma-debug.h | 8 -------- > include/linux/dma-mapping.h | 8 +++++++- > kernel/dma/debug.c | 16 ---------------- > 3 files changed, 7 insertions(+), 25 deletions(-) > > diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h > index 4208f94d93f7..2af9765d9af7 100644 > --- a/include/linux/dma-debug.h > +++ b/include/linux/dma-debug.h > @@ -18,9 +18,6 @@ struct bus_type; > > extern void dma_debug_add_bus(struct bus_type *bus); > > -extern void debug_dma_map_single(struct device *dev, const void *addr, > - unsigned long len); > - > extern void debug_dma_map_page(struct device *dev, struct page *page, > size_t offset, size_t size, > int direction, dma_addr_t dma_addr); > @@ -75,11 +72,6 @@ static inline void dma_debug_add_bus(struct bus_type *bus) > { > } > > -static inline void debug_dma_map_single(struct device *dev, const void *addr, > - unsigned long len) > -{ > -} > - > static inline void debug_dma_map_page(struct device *dev, struct page *page, > size_t offset, size_t size, > int direction, dma_addr_t dma_addr) > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 4a1c4fca475a..2d6b8382eab1 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -583,7 +583,13 @@ static inline unsigned long dma_get_merge_boundary(struct device *dev) > static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr, > size_t size, enum dma_data_direction dir, unsigned long attrs) > { > - debug_dma_map_single(dev, ptr, size); > + /* DMA must never operate on stack or other remappable places. */ > + WARN_ONCE(is_vmalloc_addr(ptr) || !virt_addr_valid(ptr),
This stands to absolutely cripple I/O performance on arm64, because every valid call will end up going off and scanning the memblock list, which is not something we want on a fastpath in non-debug configurations. We'd need a much better solution to the "pfn_valid() vs. EFI no-map" problem before this might be viable.
Robin.
> + "%s %s: driver maps %lu bytes from %s area\n", > + dev ? dev_driver_string(dev) : "unknown driver", > + dev ? dev_name(dev) : "unknown device", size, > + is_vmalloc_addr(ptr) ? "vmalloc" : "invalid"); > + > return dma_map_page_attrs(dev, virt_to_page(ptr), offset_in_page(ptr), > size, dir, attrs); > } > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 099002d84f46..aa1e6a1990b2 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -1232,22 +1232,6 @@ static void check_sg_segment(struct device *dev, struct scatterlist *sg) > #endif > } > > -void debug_dma_map_single(struct device *dev, const void *addr, > - unsigned long len) > -{ > - if (unlikely(dma_debug_disabled())) > - return; > - > - if (!virt_addr_valid(addr)) > - err_printk(dev, NULL, "device driver maps memory from invalid area [addr=%p] [len=%lu]\n", > - addr, len); > - > - if (is_vmalloc_addr(addr)) > - err_printk(dev, NULL, "device driver maps memory from vmalloc area [addr=%p] [len=%lu]\n", > - addr, len); > -} > -EXPORT_SYMBOL(debug_dma_map_single); > - > void debug_dma_map_page(struct device *dev, struct page *page, size_t offset, > size_t size, int direction, dma_addr_t dma_addr) > { >
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