Messages in this thread | | | Subject | Re: [PATCH] dma-debug: Check for drivers mapping vmalloc addresses | From | Robin Murphy <> | Date | Wed, 26 Sep 2018 14:24:42 +0100 |
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On 21/09/18 18:39, Stephen Boyd wrote: > Quoting Robin Murphy (2018-09-21 04:09:50) >> Hi Stephen, >> >> On 20/09/18 23:35, Stephen Boyd wrote: >>> I recently debugged a DMA mapping oops where a driver was trying to map >>> a buffer returned from request_firmware() with dma_map_single(). Memory >>> returned from request_firmware() is mapped into the vmalloc region and >>> this isn't a valid region to map with dma_map_single() per the DMA >>> documentation's "What memory is DMA'able?" section. >>> >>> Unfortunately, we don't really check that in the DMA debugging code, so >>> enabling DMA debugging doesn't help catch this problem. Let's add a new >>> DMA debug function to check for a vmalloc address and print a warning if >>> this happens. This makes it a little easier to debug these sorts of >>> problems, instead of seeing odd behavior or crashes when drivers attempt >>> to map the vmalloc space for DMA. >> >> Good idea! >> >>> Cc: Marek Szyprowski <m.szyprowski@samsung.com> >>> Cc: Robin Murphy <robin.murphy@arm.com> >>> Signed-off-by: Stephen Boyd <swboyd@chromium.org> >>> --- >>> include/linux/dma-debug.h | 8 ++++++++ >>> include/linux/dma-mapping.h | 1 + >>> kernel/dma/debug.c | 12 ++++++++++++ >>> 3 files changed, 21 insertions(+) >> >> However I can't help thinking this looks a little heavyweight for a >> single specific check. It seems like it would be enough to simply pass >> the VA as an extra argument to debug_dma_map_page(), since we already >> have the map_single argument which would indicate when it's valid. What >> do you reckon? > > I thought about augmenting debug_dma_map_page() but that has another > problem where those checks are done after the page has been mapped. The > kernel can oops when it's operating on the incorrect page so we need to > check things before calling the dma ops.
Oh, right, as usual I've managed to overlook a subtlety :)
In fact, with memory now jogged, I think the virt_to_page() itself is allowed to blow up if !virt_addr_valid(), so we probably do need something like your original idea to be properly robust. I guess it probably makes sense to implement that as debug_dma_map_single() then, since the purpose is really to cover any VA checks specific to that case which debug_dma_map_page() can't be expected to do after the fact.
Thanks, Robin.
> So I split that check up into pre_map and post_map parts but then that > seemed like overkill just to check for this vmalloc problem. Here's the > patch if you're interested. I can make it a little nicer if you think > it's also worthwhile. > > ---8<---- > include/linux/dma-debug.h | 8 ++++++++ > include/linux/dma-mapping.h | 3 +++ > kernel/dma/debug.c | 24 ++++++++++++++++-------- > 3 files changed, 27 insertions(+), 8 deletions(-) > > diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h > index 5aec2ca8a426..3287240a474c 100644 > --- a/include/linux/dma-debug.h > +++ b/include/linux/dma-debug.h > @@ -35,6 +35,9 @@ extern int dma_debug_resize_entries(u32 num_entries); > extern void debug_dma_check_vmalloc(struct device *dev, const void *addr, > unsigned long len); > > +extern void debug_dma_pre_map_page(struct device *dev, struct page *page, > + size_t offset, size_t size); > + > 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, > @@ -111,6 +114,11 @@ static inline void debug_dma_check_vmalloc(struct device *dev, const void *addr, > { > } > > +static inline void debug_dma_pre_map_page(struct device *dev, struct page *page, > + size_t offset, size_t size) > +{ > +} > + > 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 a0e67fd5433c..4839bbb4fdc7 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -233,6 +233,8 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr, > > BUG_ON(!valid_dma_direction(dir)); > debug_dma_check_vmalloc(dev, ptr, size); > + debug_dma_pre_map_page(dev, virt_to_page(ptr), > + offset_in_page(ptr), size); > addr = ops->map_page(dev, virt_to_page(ptr), > offset_in_page(ptr), size, > dir, attrs); > @@ -296,6 +298,7 @@ static inline dma_addr_t dma_map_page_attrs(struct device *dev, > dma_addr_t addr; > > BUG_ON(!valid_dma_direction(dir)); > + debug_dma_pre_map_page(dev, page, offset, size); > addr = ops->map_page(dev, page, offset, size, dir, attrs); > debug_dma_map_page(dev, page, offset, size, dir, addr, false); > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 7ee7978868d4..dd1ff9f7d783 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -1324,6 +1324,22 @@ void debug_dma_check_vmalloc(struct device *dev, const void *addr, > } > EXPORT_SYMBOL(debug_dma_check_vmalloc); > > +void debug_dma_pre_map_page(struct device *dev, struct page *page, size_t offset, > + size_t size) > +{ > + if (unlikely(dma_debug_disabled())) > + return; > + > + check_for_stack(dev, page, offset); > + > + if (!PageHighMem(page)) { > + void *addr = page_address(page) + offset; > + > + check_for_illegal_area(dev, addr, size); > + } > +} > +EXPORT_SYMBOL(debug_dma_pre_map_page); > + > void debug_dma_map_page(struct device *dev, struct page *page, size_t offset, > size_t size, int direction, dma_addr_t dma_addr, > bool map_single) > @@ -1352,14 +1368,6 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset, > if (map_single) > entry->type = dma_debug_single; > > - check_for_stack(dev, page, offset); > - > - if (!PageHighMem(page)) { > - void *addr = page_address(page) + offset; > - > - check_for_illegal_area(dev, addr, size); > - } > - > add_dma_entry(entry); > } > EXPORT_SYMBOL(debug_dma_map_page); >
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