[PATCH 1/2] remoteproc: mtk_scp: Fix bounds check in mt8183_scp_da_to_va()

mt8183_scp_da_to_va() translates a device address to a pointer into
SCP SRAM or DRAM. Its bounds check is wrong in two ways:

- offset is an int but is assigned from a u64. For the DRAM window,
  da = dma_addr + 0x100000010 is truncated to offset 0x10 and passes
  the check. There is also no da >= dma_addr check, so a da below
  dma_addr wraps in the u64 subtraction and can truncate to a small
  positive offset.

- (offset + len) is computed in size_t and wraps for a large len.
  With offset = 0x100 and len = (size_t)-0x80, the sum is 0x80 and
  the check passes.

da and len come from the firmware's ELF program headers
(p_paddr/p_memsz) via rproc_da_to_va(), and the returned pointer is
then written to by the ELF loader, so a malformed firmware image can
make the loader write outside the intended region.

Use a u64 offset, check da >= dma_addr before subtracting, and
compare len against the remaining window size instead of adding it
to offset.

Fixes: 63c13d61eafe ("remoteproc/mediatek: add SCP support for mt8183")
Cc: stable@vger.kernel.org
Signed-off-by: Atul Akella <redacted>
---
 drivers/remoteproc/mtk_scp.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
index 9751acc2bf83..d18ae676260a 100644
--- a/drivers/remoteproc/mtk_scp.c
+++ b/drivers/remoteproc/mtk_scp.c

@@ -754,17 +754,19 @@ static int scp_start(struct rproc *rproc)
 
 static void *mt8183_scp_da_to_va(struct mtk_scp *scp, u64 da, size_t len)
 {
-	int offset;
+	u64 offset;
 	const struct mtk_scp_sizes_data *scp_sizes;
 
 	scp_sizes = scp->data->scp_sizes;
 	if (da < scp->sram_size) {
 		offset = da;
-		if (offset >= 0 && (offset + len) <= scp->sram_size)
+		if (len <= scp->sram_size - offset)
 			return (void __force *)scp->sram_base + offset;
 	} else if (scp_sizes->max_dram_size) {
 		offset = da - scp->dma_addr;
-		if (offset >= 0 && (offset + len) <= scp_sizes->max_dram_size)
+		if (da >= scp->dma_addr &&
+		    offset <= scp_sizes->max_dram_size &&
+		    len <= scp_sizes->max_dram_size - offset)
 			return scp->cpu_addr + offset;
 	}
 

-- 
2.43.0