[PATCH v19 01/14] cxl/ras: Fix cxl_rch_get_aer_info() out-of-bounds AER register read

[Terry Bowman <terry.bowman@amd.com>]

cxl_rch_get_aer_info() copies the RCH Downstream Port AER capability from
the RCRB MMIO block using a readl() loop bounded by sizeof(struct
aer_capability_regs). This struct is a software layout and its embedded
struct pcie_tlp_log is larger than the on-wire AER capability. As a
result the loop reads past the mapped AER register block.

The over-read also populates the software-only tail fields including
header_log.header_len. An out-of-range header_len passed to
pcie_print_tlp_log() can then loop past the header log buffer and cause
a second out-of-bounds read.

The read was correct when introduced, but struct pcie_tlp_log has since
grown (Header Log and TLP Prefix Log sizes, header_len and flit fields),
so sizeof(struct aer_capability_regs) no longer matches the physical AER
capability.

Bound the read to the physical AER registers, header through the 16 byte
Header Log. Zero the destination first so the software-only fields are
deterministic.

Fixes: 6ac07883dbb5 ("cxl/pci: Add RCH downstream port error logging")
Reported-by: Sashiko <sashiko@linuxfoundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Terry Bowman <terry.bowman@amd.com>

---

Changes in v18 -> v19:
- New patch, split from "cxl/ras: Fix cxl_rch_get_aer_severity() wrong
  severity register". Addresses out-of-bounds RCRB MMIO read that
  Sashiko flagged against the combined v18 patch.
---
 drivers/cxl/core/ras_rch.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/ras_rch.c b/drivers/cxl/core/ras_rch.c
index 0a8b3b9b63884..8a3965edaa12c 100644
--- a/drivers/cxl/core/ras_rch.c
+++ b/drivers/cxl/core/ras_rch.c
@@ -58,13 +58,28 @@ void cxl_disable_rch_root_ints(struct cxl_dport *dport)
 static bool cxl_rch_get_aer_info(void __iomem *aer_base,
 				 struct aer_capability_regs *aer_regs)
 {
-	int read_cnt = sizeof(struct aer_capability_regs) / sizeof(u32);
+	/*
+	 * Bound the copy to the physically-defined AER registers (header
+	 * through the 16-byte Header Log). struct aer_capability_regs is a
+	 * software layout whose embedded struct pcie_tlp_log is larger than
+	 * the on-wire AER capability; copying sizeof(*aer_regs) would
+	 * over-read the RCRB-mapped MMIO block.
+	 */
+	int read_cnt = (PCI_ERR_HEADER_LOG + 16) / sizeof(u32);
 	u32 *aer_regs_buf = (u32 *)aer_regs;
 	int n;
 
 	if (!aer_base)
 		return false;
 
+	/*
+	 * Zero the destination so the software-only tail fields
+	 * (e.g. header_log.header_len) are deterministic rather than
+	 * left as uninitialized stack, which could drive a bogus loop
+	 * length in pcie_print_tlp_log().
+	 */
+	memset(aer_regs, 0, sizeof(*aer_regs));
+
 	/* Use readl() to guarantee 32-bit accesses */
 	for (n = 0; n < read_cnt; n++)
 		aer_regs_buf[n] = readl(aer_base + n * sizeof(u32));
-- 
2.34.1