[PATCH v12 04/19] PCI: Reject unreadable ACS controls in isolation checks

[Leon Romanovsky]

From: Leon Romanovsky <leonro@xxxxxxxxxx>

pci_acs_flags_enabled() and the Intel SPT PCH quirk use ACS registers
without checking config-space read errors. A failed read may leave control
state indeterminate yet allow the device to satisfy requested isolation
controls. So can a read that returns all ones with a successful status,
which is what a device that does not answer usually produces.

Return false when either ACS capability or control state cannot be read
or reads as all ones, which neither register can legitimately hold. An
unknown state cannot prove isolation.

Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Tested-by: Tushar Dave <tdave@xxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
 drivers/pci/pci.c    | 4 +++-
 drivers/pci/quirks.c | 8 ++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7c6f2aba8144..6d677695c0f5 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3627,7 +3627,9 @@ static bool pci_acs_flags_enabled(struct pci_dev *pdev, u16 acs_flags)
 	 */
 	acs_flags &= (pdev->acs_capabilities | PCI_ACS_EC);
 
-	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
+	if (pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl) ||
+	    PCI_POSSIBLE_ERROR(ctrl))
+		return false;
 	return (ctrl & acs_flags) == acs_flags;
 }
 
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 7f1f47ea2ee4..05605c3afe08 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5145,10 +5145,14 @@ static int pci_quirk_intel_spt_pch_acs(struct pci_dev *dev, u16 acs_flags)
 		return -ENOTTY;
 
 	/* see pci_acs_flags_enabled() */
-	pci_read_config_dword(dev, pos + PCI_ACS_CAP, &cap);
+	if (pci_read_config_dword(dev, pos + PCI_ACS_CAP, &cap) ||
+	    PCI_POSSIBLE_ERROR(cap))
+		return 0;
 	acs_flags &= (cap | PCI_ACS_EC);
 
-	pci_read_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, &ctrl);
+	if (pci_read_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, &ctrl) ||
+	    PCI_POSSIBLE_ERROR(ctrl))
+		return 0;
 
 	return pci_acs_ctrl_enabled(acs_flags, ctrl);
 }

-- 
2.56.0