[PATCH v5] PCI: mediatek: Fix integer truncation and handle oversized resources

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

resource_size() returns a resource_size_t, which can be 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 bits.

Furthermore, AHB2PCIE_SIZE() uses a 5-bit mask GENMASK(4, 0). If
the size order exceeds the range representable by this field,
higher bits are discarded by the mask. This can leave the hardware
translation window smaller than the OS resource, causing bus
errors when accessing BARs in the unmapped upper region.

Fix this by using fls64(size) to calculate the size order without
truncating the resource size, and return -EINVAL if the size order
exceeds the supported range.

Changelog:

- v5: Use fls64(size) instead of fls64(size - 1) and remove the
  redundant zero-size check.
- v4: Fix struct device pointer access (pcie->dev) for dev_err().
  Verified build and passed Sashiko review checks.
  [Subject: PCI: mediatek: Fix integer truncation and handle
  oversized resources]
- v3: Replace clamping logic with strict size validation
  (size_order > 31 returns -EINVAL), add a zero-size check,
  and update size calculation to fls64(size - 1).
  [Subject: PCI: mediatek: Fix integer truncation and handle
  oversized resources]
- v2: Add size clamping for size_order > 31 to prevent overflowing
  the 5-bit AHB2PCIE_SIZE() macro mask.
  [Subject: PCI: mediatek: Fix integer truncation in fls()
  and clamp size]
- v1: Initial submission using fls64() to handle 64-bit resource
  sizes and prevent integer truncation.
  [Subject: PCI: mediatek: Fix integer truncation in fls()
  for resource size]

Signed-off-by: Sreeraj S Kurup <sreekuttan2156239@gmail.com>
---
 drivers/pci/controller/pcie-mediatek.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
index 3a3e91cd0c21..6821452a82b6 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 +756,15 @@ 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);
+	size_order = fls64(size);
+	if (size_order > 31) {
+		dev_err(pcie->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 +785,8 @@ 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 +841,15 @@ 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);
+	size_order = fls64(size);
+	if (size_order > 31) {
+		dev_err(pcie->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