[PATCH net] pds_core: fix cmd_regs access racing BAR unmap on reset

["Nikhil P. Rao" <nikhil.rao@amd.com>]

pdsc_reset_prepare() and pdsc_reset_done()'s pdsc_map_bars() error path
clear/iounmap cmd_regs without devcmd_lock, and pdsc_firmware_update()'s
download loop derefs cmd_regs after dropping and retaking the lock
without re-checking. An FLR concurrent with a devlink flash can unmap
cmd_regs under an in-flight devcmd, causing a NULL deref or a write to
unmapped MMIO.

Take devcmd_lock across the BAR unmap/remap. Only the PF maps cmd_regs
and runs devcmd, so guard the locking to the PF.

pdsc_unmap_bars() also clears info_regs, which has its own readers under
config_lock (and a lockless debugfs reader); that teardown race is
pre-existing and handled separately.

Fixes: e96094c1d11c ("pds_core: Clear BARs on reset")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260708212222.296202-1-nikhil.rao%40amd.com?part=3
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Nikhil P. Rao <nikhil.rao@amd.com>
---
 drivers/net/ethernet/amd/pds_core/fw.c   |  6 ++++++
 drivers/net/ethernet/amd/pds_core/main.c | 10 +++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/amd/pds_core/fw.c b/drivers/net/ethernet/amd/pds_core/fw.c
index fa626719e68d..cd7616ed9ef3 100644
--- a/drivers/net/ethernet/amd/pds_core/fw.c
+++ b/drivers/net/ethernet/amd/pds_core/fw.c
@@ -134,6 +134,12 @@ int pdsc_firmware_update(struct pdsc *pdsc, const struct firmware *fw,
 
 		copy_sz = min_t(unsigned int, buf_sz, fw->size - offset);
 		mutex_lock(&pdsc->devcmd_lock);
+		if (!pdsc->cmd_regs) {
+			mutex_unlock(&pdsc->devcmd_lock);
+			err = -ENXIO;
+			NL_SET_ERR_MSG_MOD(extack, "Device reset during flash");
+			goto err_out;
+		}
 		memcpy_toio(&pdsc->cmd_regs->data, fw->data + offset, copy_sz);
 		err = pdsc_devcmd_fw_download_locked(pdsc, data_addr,
 						     offset, copy_sz);
diff --git a/drivers/net/ethernet/amd/pds_core/main.c b/drivers/net/ethernet/amd/pds_core/main.c
index 8d94a4d70395..08af92b47d7d 100644
--- a/drivers/net/ethernet/amd/pds_core/main.c
+++ b/drivers/net/ethernet/amd/pds_core/main.c
@@ -501,7 +501,13 @@ static void pdsc_reset_prepare(struct pci_dev *pdev)
 		pdsc_auxbus_dev_del(pdsc, pdsc, &pdsc->padev);
 	}
 
-	pdsc_unmap_bars(pdsc);
+	if (!pdev->is_virtfn) {
+		mutex_lock(&pdsc->devcmd_lock);
+		pdsc_unmap_bars(pdsc);
+		mutex_unlock(&pdsc->devcmd_lock);
+	} else {
+		pdsc_unmap_bars(pdsc);
+	}
 	pci_release_regions(pdev);
 	if (pci_is_enabled(pdev))
 		pci_disable_device(pdev);
@@ -530,7 +536,9 @@ static void pdsc_reset_done(struct pci_dev *pdev)
 			return;
 		}
 
+		mutex_lock(&pdsc->devcmd_lock);
 		err = pdsc_map_bars(pdsc);
+		mutex_unlock(&pdsc->devcmd_lock);
 		if (err)
 			return;
 	}
-- 
2.43.0