[PATCH net-next v2] net: mana: Use at least SZ_4K in doorbell ID range check

[Erni Sri Satya Vennela <ernis@linux.microsoft.com>]

mana_gd_ring_doorbell() accesses offsets up to DOORBELL_OFFSET_EQ
(0xFF8) + 8 bytes = 4KB within each doorbell page. A db_page_size
smaller than SZ_4K is fundamentally incompatible with the driver:
doorbell pages would overlap and the device cannot function correctly.

Validate db_page_size at the source and fail the
probe early if the value is below SZ_4K. This ensures the doorbell ID
range check in mana_gd_register_device() can rely on db_page_size
being valid.

Fixes: 89fe91c65992 ("net: mana: hardening: Validate doorbell ID from GDMA_REGISTER_DEVICE response")
Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
---
Changes in v2:
* Remove "db_page_sz = max_t(u64, SZ_4K, gc->db_page_size)" in
  mana_gd_register_device and validate db_page_sz at the source
  mana_gf_init_pf_regs and mana_gd_init_vf_regs.
* Update commit message.
---
 .../net/ethernet/microsoft/mana/gdma_main.c   | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c b/drivers/net/ethernet/microsoft/mana/gdma_main.c
index 2ba1fa3336f9..43741cd35af8 100644
--- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
+++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
@@ -4,6 +4,7 @@
 #include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/sizes.h>
 #include <linux/utsname.h>
 #include <linux/version.h>
 #include <linux/msi.h>
@@ -46,6 +47,18 @@ static int mana_gd_init_pf_regs(struct pci_dev *pdev)
 	u64 sriov_base_off;
 
 	gc->db_page_size = mana_gd_r32(gc, GDMA_PF_REG_DB_PAGE_SIZE) & 0xFFFF;
+
+	/* mana_gd_ring_doorbell() accesses offsets up to DOORBELL_OFFSET_EQ
+	 * (0xFF8) + 8 bytes = 4KB within each doorbell page, so the page
+	 * size must be at least SZ_4K.
+	 */
+	if (gc->db_page_size < SZ_4K) {
+		dev_err(gc->dev,
+			"Doorbell page size %llu too small (min %u)\n",
+			gc->db_page_size, SZ_4K);
+		return -EPROTO;
+	}
+
 	gc->db_page_off = mana_gd_r64(gc, GDMA_PF_REG_DB_PAGE_OFF);
 
 	/* Validate doorbell offset is within BAR0 */
@@ -73,6 +86,18 @@ static int mana_gd_init_vf_regs(struct pci_dev *pdev)
 	struct gdma_context *gc = pci_get_drvdata(pdev);
 
 	gc->db_page_size = mana_gd_r32(gc, GDMA_REG_DB_PAGE_SIZE) & 0xFFFF;
+
+	/* mana_gd_ring_doorbell() accesses offsets up to DOORBELL_OFFSET_EQ
+	 * (0xFF8) + 8 bytes = 4KB within each doorbell page, so the page
+	 * size must be at least SZ_4K.
+	 */
+	if (gc->db_page_size < SZ_4K) {
+		dev_err(gc->dev,
+			"Doorbell page size %llu too small (min %u)\n",
+			gc->db_page_size, SZ_4K);
+		return -EPROTO;
+	}
+
 	gc->db_page_off = mana_gd_r64(gc, GDMA_REG_DB_PAGE_OFFSET);
 
 	/* Validate doorbell offset is within BAR0 */
-- 
2.34.1