cxl/pci: Rightsize CDAT response allocation

Jonathan notes that cxl_cdat_get_length() and cxl_cdat_read_table()
allocate 32 dwords for the DOE response even though it may be smaller.

In the case of cxl_cdat_get_length(), only the second dword of the
response is of interest (it contains the length).  So reduce the
allocation to 2 dwords and let DOE discard the remainder.

In the case of cxl_cdat_read_table(), a correctly sized allocation for
the full CDAT already exists.  Let DOE write each table entry directly
into that allocation.  There's a snag in that the table entry is
preceded by a Table Access Response Header (1 dword, CXL 3.0 table 8-14).
Save the last dword of the previous table entry, let DOE overwrite it
with the header of the next entry and restore it afterwards.

The resulting CDAT is preceded by 4 unavoidable useless bytes.  Increase
the allocation size accordingly.

The buffer overflow check in cxl_cdat_read_table() becomes unnecessary
because the remaining bytes in the allocation are tracked in "length",
which is passed to DOE and limits how many bytes it writes to the
allocation.  Additionally, cxl_cdat_read_table() bails out if the DOE
response is truncated due to insufficient space.

Tested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/7a4e1f86958a79a70f29b96a92199522f08f8322.1678543498.git.lukas@wunner.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index 0609bd629073eb02462cae28b1971e57c93ff444..25b7e8125d5de67971e2552024fc8e3030303fa9 100644 (file)
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -453,7 +453,7 @@ static int cxl_cdat_get_length(struct device *dev,
                               size_t *length)
 {
        __le32 request = CDAT_DOE_REQ(0);
-       __le32 response[32];
+       __le32 response[2];
        int rc;
 
        rc = pci_doe(cdat_doe, PCI_DVSEC_VENDOR_ID_CXL,
@@ -464,7 +464,7 @@ static int cxl_cdat_get_length(struct device *dev,
                dev_err(dev, "DOE failed: %d", rc);
                return rc;
        }
-       if (rc < 2 * sizeof(__le32))
+       if (rc < sizeof(response))
                return -EIO;
 
        *length = le32_to_cpu(response[1]);
@@ -477,28 +477,28 @@ static int cxl_cdat_read_table(struct device *dev,
                               struct pci_doe_mb *cdat_doe,
                               void *cdat_table, size_t *cdat_length)
 {
-       size_t length = *cdat_length;
+       size_t length = *cdat_length + sizeof(__le32);
        __le32 *data = cdat_table;
        int entry_handle = 0;
+       __le32 saved_dw = 0;
 
        do {
                __le32 request = CDAT_DOE_REQ(entry_handle);
                struct cdat_entry_header *entry;
-               __le32 response[32];
                size_t entry_dw;
                int rc;
 
                rc = pci_doe(cdat_doe, PCI_DVSEC_VENDOR_ID_CXL,
                             CXL_DOE_PROTOCOL_TABLE_ACCESS,
                             &request, sizeof(request),
-                            &response, sizeof(response));
+                            data, length);
                if (rc < 0) {
                        dev_err(dev, "DOE failed: %d", rc);
                        return rc;
                }
 
                /* 1 DW Table Access Response Header + CDAT entry */
-               entry = (struct cdat_entry_header *)(response + 1);
+               entry = (struct cdat_entry_header *)(data + 1);
                if ((entry_handle == 0 &&
                     rc != sizeof(__le32) + sizeof(struct cdat_header)) ||
                    (entry_handle > 0 &&
@@ -508,21 +508,22 @@ static int cxl_cdat_read_table(struct device *dev,
 
                /* Get the CXL table access header entry handle */
                entry_handle = FIELD_GET(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE,
-                                        le32_to_cpu(response[0]));
+                                        le32_to_cpu(data[0]));
                entry_dw = rc / sizeof(__le32);
                /* Skip Header */
                entry_dw -= 1;
-               entry_dw = min(length / sizeof(__le32), entry_dw);
-               /* Prevent length < 1 DW from causing a buffer overflow */
-               if (entry_dw) {
-                       memcpy(data, entry, entry_dw * sizeof(__le32));
-                       length -= entry_dw * sizeof(__le32);
-                       data += entry_dw;
-               }
+               /*
+                * Table Access Response Header overwrote the last DW of
+                * previous entry, so restore that DW
+                */
+               *data = saved_dw;
+               length -= entry_dw * sizeof(__le32);
+               data += entry_dw;
+               saved_dw = *data;
        } while (entry_handle != CXL_DOE_TABLE_ACCESS_LAST_ENTRY);
 
        /* Length in CDAT header may exceed concatenation of CDAT entries */
-       *cdat_length -= length;
+       *cdat_length -= length - sizeof(__le32);
 
        return 0;
 }
@@ -559,7 +560,8 @@ void read_cdat_data(struct cxl_port *port)
                return;
        }
 
-       cdat_table = devm_kzalloc(dev, cdat_length, GFP_KERNEL);
+       cdat_table = devm_kzalloc(dev, cdat_length + sizeof(__le32),
+                                 GFP_KERNEL);
        if (!cdat_table)
                return;
 
@@ -570,7 +572,7 @@ void read_cdat_data(struct cxl_port *port)
                dev_err(dev, "CDAT data read error\n");
        }
 
-       port->cdat.table = cdat_table;
+       port->cdat.table = cdat_table + sizeof(__le32);
        port->cdat.length = cdat_length;
 }
 EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);