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Subject[PATCH 4/4] dma-debug: Allow poisoning nonzero allocations
Date
Since some dma_alloc_coherent implementations return a zeroed buffer
regardless of whether __GFP_ZERO is passed, there exist drivers which
are implicitly dependent on this and pass otherwise uninitialised
buffers to hardware. This can lead to subtle and awkward-to-debug issues
using those drivers on different platforms, where nonzero uninitialised
junk may for instance occasionally look like a valid command which
causes the hardware to start misbehaving. To help with debugging such
issues, add the option to make uninitialised buffers much more obvious.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
include/asm-generic/dma-mapping-common.h | 2 +-
include/linux/dma-debug.h | 6 ++++--
include/linux/poison.h | 3 +++
lib/Kconfig.debug | 10 ++++++++++
lib/dma-debug.c | 6 +++++-
5 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/dma-mapping-common.h b/include/asm-generic/dma-mapping-common.h
index b1bc954..0f3e16b 100644
--- a/include/asm-generic/dma-mapping-common.h
+++ b/include/asm-generic/dma-mapping-common.h
@@ -260,7 +260,7 @@ static inline void *dma_alloc_attrs(struct device *dev, size_t size,
return NULL;

cpu_addr = ops->alloc(dev, size, dma_handle, flag, attrs);
- debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr);
+ debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr, flag);
return cpu_addr;
}

diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h
index fe8cb61..e5f539d 100644
--- a/include/linux/dma-debug.h
+++ b/include/linux/dma-debug.h
@@ -51,7 +51,8 @@ extern void debug_dma_unmap_sg(struct device *dev, struct scatterlist *sglist,
int nelems, int dir);

extern void debug_dma_alloc_coherent(struct device *dev, size_t size,
- dma_addr_t dma_addr, void *virt);
+ dma_addr_t dma_addr, void *virt,
+ gfp_t flags);

extern void debug_dma_free_coherent(struct device *dev, size_t size,
void *virt, dma_addr_t addr);
@@ -132,7 +133,8 @@ static inline void debug_dma_unmap_sg(struct device *dev,
}

static inline void debug_dma_alloc_coherent(struct device *dev, size_t size,
- dma_addr_t dma_addr, void *virt)
+ dma_addr_t dma_addr, void *virt,
+ gfp_t flags)
{
}

diff --git a/include/linux/poison.h b/include/linux/poison.h
index 317e16d..174104e 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -73,6 +73,9 @@
#define MUTEX_DEBUG_INIT 0x11
#define MUTEX_DEBUG_FREE 0x22

+/********** lib/dma_debug.c **********/
+#define DMA_ALLOC_POISON 0xee
+
/********** lib/flex_array.c **********/
#define FLEX_ARRAY_FREE 0x6c /* for use-after-free poisoning */

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ab76b99..f2da7a1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1752,6 +1752,16 @@ config DMA_API_DEBUG

If unsure, say N.

+config DMA_API_DEBUG_POISON
+ bool "Poison coherent DMA buffers"
+ depends on DMA_API_DEBUG && EXPERT
+ help
+ Poison DMA buffers returned by dma_alloc_coherent unless __GFP_ZERO
+ is explicitly specified, to catch drivers depending on zeroed buffers
+ without passing the correct flags.
+
+ Only say Y if you're prepared for almost everything to break.
+
config TEST_LKM
tristate "Test module loading with 'hello world' module"
default n
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 908fb35..40514ed 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -30,6 +30,7 @@
#include <linux/sched.h>
#include <linux/ctype.h>
#include <linux/list.h>
+#include <linux/poison.h>
#include <linux/slab.h>

#include <asm/sections.h>
@@ -1447,7 +1448,7 @@ void debug_dma_unmap_sg(struct device *dev, struct scatterlist *sglist,
EXPORT_SYMBOL(debug_dma_unmap_sg);

void debug_dma_alloc_coherent(struct device *dev, size_t size,
- dma_addr_t dma_addr, void *virt)
+ dma_addr_t dma_addr, void *virt, gfp_t flags)
{
struct dma_debug_entry *entry;

@@ -1457,6 +1458,9 @@ void debug_dma_alloc_coherent(struct device *dev, size_t size,
if (unlikely(virt == NULL))
return;

+ if (IS_ENABLED(CONFIG_DMA_API_DEBUG_POISON) && !(flags & __GFP_ZERO))
+ memset(virt, DMA_ALLOC_POISON, size);
+
entry = dma_entry_alloc();
if (!entry)
return;
--
1.9.1


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