[PATCH 6.12.y 6/6] PCI: Skip Resizable BAR restore on read error

[Sasha Levin <sashal@kernel.org>]

From: Marco Nenciarini <mnencia@kcore.it>

[ Upstream commit ee7471fe968d210939be9046089a924cd23c8c3b ]

pci_restore_rebar_state() uses the Resizable BAR Control register to decide
how many BARs to restore (nbars) and which BAR each iteration addresses
(bar_idx).

When a device does not respond, config reads typically return
PCI_ERROR_RESPONSE (~0).  Both fields are 3 bits wide, so nbars and bar_idx
both evaluate to 7, past the spec's valid ranges for both fields.
pci_resource_n() then returns an unrelated resource slot, whose size is
used to derive a nonsensical value written back to the Resizable BAR
Control register.

Bail out if any Resizable BAR Control read returns PCI_ERROR_RESPONSE. No
further BARs are touched, which is safe because a config read that returns
PCI_ERROR_RESPONSE indicates the device is unreachable and restoration is
pointless.

Fixes: d3252ace0bc6 ("PCI: Restore resized BAR state on resume")
Signed-off-by: Marco Nenciarini <mnencia@kcore.it>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/666cac19b5daa0ab0e0ab64454e76b4d24465dbd.1776429882.git.mnencia@kcore.it
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/pci/rebar.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/rebar.c b/drivers/pci/rebar.c
index 0d6efefdc56ade..548894a3fad5cf 100644
--- a/drivers/pci/rebar.c
+++ b/drivers/pci/rebar.c
@@ -130,6 +130,9 @@ void pci_restore_rebar_state(struct pci_dev *pdev)
 		return;
 
 	pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+	if (PCI_POSSIBLE_ERROR(ctrl))
+		return;
+
 	nbars = FIELD_GET(PCI_REBAR_CTRL_NBAR_MASK, ctrl);
 
 	for (i = 0; i < nbars; i++, pos += 8) {
@@ -137,6 +140,9 @@ void pci_restore_rebar_state(struct pci_dev *pdev)
 		int bar_idx, size;
 
 		pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+		if (PCI_POSSIBLE_ERROR(ctrl))
+			return;
+
 		bar_idx = ctrl & PCI_REBAR_CTRL_BAR_IDX;
 		res = pci_resource_n(pdev, bar_idx);
 		size = pci_rebar_bytes_to_size(resource_size(res));
-- 
2.53.0