[PATCH v3] PCI: mediatek: Fix integer truncation and handle oversized resources

[Sreeraj S Kurup <sreekuttan2156239@gmail.com>]

resource_size() returns a resource_size_t, which is 64-bit on 64-bit
architectures or 32-bit systems with LPAE/PAE enabled. Passing this
directly to fls(), which accepts an unsigned int, implicitly
truncates the upper 32 bits.

Furthermore, AHB2PCIE_SIZE() uses a 5-bit mask GENMASK(4, 0). If a
resource size exceeds 2 GiB (order > 31), the log2 size order
overflows the 5-bit mask. Clamping the value silently truncates the
hardware window while leaving the OS resource intact, causing bus
errors when accessing BARs in the unmapped upper region.

Fix this by using fls64(size - 1) to accurately calculate log2 size
orders without off-by-one errors and returning -EINVAL if the resource
size exceeds the maximum supported 31-bit window order.

Signed-off-by: Sreeraj S Kurup <sreekuttan2156239@gmail.com>
---
 drivers/pci/controller/pcie-mediatek.c | 29 ++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
index a60d1ae076f8..97d13c9d3369 100644
--- a/drivers/pci/controller/pcie-mediatek.c
+++ b/drivers/pci/controller/pcie-mediatek.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/bitops.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/errno.h>
@@ -686,6 +687,8 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
 	const struct mtk_pcie_soc *soc = port->pcie->soc;
 	u32 val;
 	int err;
+	resource_size_t size;
+	int size_order;
 
 	entry = resource_list_first_type(&host->windows, IORESOURCE_MEM);
 	if (entry)
@@ -753,8 +756,18 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
 		mtk_pcie_enable_msi(port);
 
 	/* Set AHB to PCIe translation windows */
+	size = resource_size(mem);
+	if (!size)
+		return -EINVAL;
+
+	size_order = fls64(size - 1);
+	if (size_order > 31) {
+		dev_err(port->dev, "Memory resource size too large: %pa\n", &size);
+		return -EINVAL;
+	}
+
 	val = lower_32_bits(mem->start) |
-	      AHB2PCIE_SIZE(fls(resource_size(mem)));
+	      AHB2PCIE_SIZE(size_order);
 	writel(val, port->base + PCIE_AHB_TRANS_BASE0_L);
 
 	val = upper_32_bits(mem->start);
@@ -775,6 +788,8 @@ static int mtk_pcie_startup_port_en7528(struct mtk_pcie_port *port)
 	struct resource_entry *entry;
 	u32 val, link_mask;
 	int err;
+	resource_size_t size;
+	int size_order;
 
 	entry = resource_list_first_type(&host->windows, IORESOURCE_MEM);
 	if (entry)
@@ -829,8 +844,18 @@ static int mtk_pcie_startup_port_en7528(struct mtk_pcie_port *port)
 		mtk_pcie_enable_msi(port);
 
 	/* Set AHB to PCIe translation windows */
+	size = resource_size(mem);
+	if (!size)
+		return -EINVAL;
+
+	size_order = fls64(size - 1);
+	if (size_order > 31) {
+		dev_err(port->dev, "Memory resource size too large: %pa\n", &size);
+		return -EINVAL;
+	}
+
 	val = lower_32_bits(mem->start) |
-	      AHB2PCIE_SIZE(fls(resource_size(mem)));
+	      AHB2PCIE_SIZE(size_order);
 	writel(val, port->base + PCIE_AHB_TRANS_BASE0_L);
 
 	val = upper_32_bits(mem->start);
-- 
2.55.0