[PATCH 2/4] PCI: endpoint: pci-epf-test: Sanity-check doorbell offset within BAR

pci-epf-test advertises the doorbell target to the RC as a BAR number
and an offset. The RC rings the doorbell with a single DWORD MMIO write
to BAR + offset.

For MSI/MSI-X-based doorbells, the message address is required to be
DWORD-aligned, so the computed offset should not straddle a BAR boundary
in normal operation.

However, with support for doorbells based on mechanisms other than
MSI/MSI-X (via pci_epf_alloc_doorbell()), the returned message address
may not necessarily be DWORD-aligned. In such a case, offset plus the
32-bit write width could cross the end of the BAR aperture. The offset
returned by pci_epf_align_inbound_addr() is guaranteed to be within the
BAR size, but this alone does not ensure that a 32-bit write starting at
that offset stays within the BAR.

Add a bounds check to ensure that the 32-bit doorbell write always stays
within the BAR aperture. While this should not trigger for
spec-compliant MSI/MSI-X addresses, it provides a defensive guard
against unexpected offsets from future doorbell implementations.

Suggested-by: Niklas Cassel <[email protected]>
Signed-off-by: Koichiro Den <[email protected]>
---
 drivers/pci/endpoint/functions/pci-epf-test.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index 0cb7af0919dc..148a34e51f6b 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -761,6 +761,9 @@ static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
 	if (ret)
 		goto err_doorbell_cleanup;
 
+	if (size_add(offset, sizeof(u32)) > epf->bar[bar].size)
+		goto err_doorbell_cleanup;
+
 	reg->doorbell_offset = cpu_to_le32(offset);
 
 	epf_test->db_bar.barno = bar;
-- 
2.51.0