[PATCH 12/21] dmaengine: stm32-dma: Annotate struct stm32_dma_desc with __counted_by

Kees Cook
2023-08-18T00:00:10Z

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct stm32_dma_desc.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Vinod Koul <vkoul@kernel.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: dmaengine@vger.kernel.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/dma/stm32-dma.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 5c36811aa134..a732b3807b11 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -191,7 +191,7 @@ struct stm32_dma_desc {
struct virt_dma_desc vdesc;
bool cyclic;
u32 num_sgs;
- struct stm32_dma_sg_req sg_req[];
+ struct stm32_dma_sg_req sg_req[] __counted_by(num_sgs);
};

/**
@@ -1105,6 +1105,7 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_slave_sg(
desc = kzalloc(struct_size(desc, sg_req, sg_len), GFP_NOWAIT);
if (!desc)
return NULL;
+ desc->num_sgs = sg_len;

/* Set peripheral flow controller */
if (chan->dma_sconfig.device_fc)
@@ -1141,8 +1142,6 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_slave_sg(
desc->sg_req[i].chan_reg.dma_sm1ar += sg_dma_len(sg);
desc->sg_req[i].chan_reg.dma_sndtr = nb_data_items;
}
-
- desc->num_sgs = sg_len;
desc->cyclic = false;

return vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);
@@ -1216,6 +1215,7 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_cyclic(
desc = kzalloc(struct_size(desc, sg_req, num_periods), GFP_NOWAIT);
if (!desc)
return NULL;
+ desc->num_sgs = num_periods;

for (i = 0; i < num_periods; i++) {
desc->sg_req[i].len = period_len;
@@ -1232,8 +1232,6 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_cyclic(
if (!chan->trig_mdma)
buf_addr += period_len;
}
-
- desc->num_sgs = num_periods;
desc->cyclic = true;

return vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);
@@ -1254,6 +1252,7 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_memcpy(
desc = kzalloc(struct_size(desc, sg_req, num_sgs), GFP_NOWAIT);
if (!desc)
return NULL;
+ desc->num_sgs = num_sgs;

threshold = chan->threshold;

@@ -1283,8 +1282,6 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_memcpy(
desc->sg_req[i].chan_reg.dma_sndtr = xfer_count;
desc->sg_req[i].len = xfer_count;
}
-
- desc->num_sgs = num_sgs;
desc->cyclic = false;

return vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);
--
2.34.1