dmaengine: stm32-dma: Annotate struct stm32_dma_desc with __counted_by

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>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230817235859.49846-12-keescook@chromium.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 5c36811aa1342c8df4f340dbbaeadbd77c8ef3bf..a732b3807b111e9211f470fd7ba57a42fdc1ffd0 100644 (file)
--- 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);