[PATCH] cxl/acpi: Restore HBIW check before dereferencing platform_data

[Alison Schofield <alison.schofield@intel.com>]

Commit 4fe516d2ad1a ("cxl/acpi: Make the XOR calculations available
for testing") split xormap handling code to create a reusable helper
function but inadvertently dropped the check of HBIW values before
dereferencing cxlrd->platform_data. When HBIW is 1 or 3, no xormaps
are needed and platform_data may be NULL, leading to a potential NULL
pointer dereference.

Affects platform configs using XOR Arithmetic with HBIWs of 1 or 3,
when performing DPA->HPA address translation for CXL events. Those
events would be any of poison ops, general media, or dram.

Restore the early return check for HBIW values of 1 and 3 before
dereferencing platform_data.

Fixes: 4fe516d2ad1a ("cxl/acpi: Make the XOR calculations available for testing")
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
---

This bug was introduced in 6.19-rc1 and found while rebasing this
work: cxl/region: Translate DPA->HPA in unaligned MOD3 regions.
Adding coverage for this to cxl-test suite is on my todo list.

 drivers/cxl/acpi.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 77ac940e3013..49bba2b9a3c4 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -75,9 +75,16 @@ EXPORT_SYMBOL_FOR_MODULES(cxl_do_xormap_calc, "cxl_translate");
 
 static u64 cxl_apply_xor_maps(struct cxl_root_decoder *cxlrd, u64 addr)
 {
-	struct cxl_cxims_data *cximsd = cxlrd->platform_data;
+	int hbiw = cxlrd->cxlsd.nr_targets;
+	struct cxl_cxims_data *cximsd;
 
-	return cxl_do_xormap_calc(cximsd, addr, cxlrd->cxlsd.nr_targets);
+	/* No xormaps for host bridge interleave ways of 1 or 3 */
+	if (hbiw == 1 || hbiw == 3)
+		return addr;
+
+	cximsd = cxlrd->platform_data;
+
+	return cxl_do_xormap_calc(cximsd, addr, hbiw);
 }
 
 struct cxl_cxims_context {

base-commit: 9ace4753a5202b02191d54e9fdf7f9e3d02b85eb
-- 
2.37.3