Per CXL Spec r3.1 Table 9-21, both CXL1.1 and CXL2.0 have defined their
own length, verify it to avoid an invalid CHBS

This patch also wraps some sanity checks into a function.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
 drivers/cxl/acpi.c | 45 +++++++++++++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index cb14829bb9be..4a82d2d8b547 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -11,8 +11,6 @@
 #include "cxlpci.h"
 #include "cxl.h"
 
-#define CXL_RCRB_SIZE	SZ_8K
-
 struct cxl_cxims_data {
 	int nr_maps;
 	u64 xormaps[] __counted_by(nr_maps);
@@ -468,8 +466,35 @@ struct cxl_chbs_context {
 	u32 cxl_version;
 	int nr_versions;
 	u32 saved_version;
+	u32 length;
 };
 
+static bool cxl_chbs_verify(struct device *dev, struct cxl_chbs_context ctx)
+{
+	if (ctx.cxl_version == UINT_MAX) {
+		dev_warn(dev, "No CHBS found for Host Bridge (UID %lld)\n",
+			 ctx.uid);
+		return false;
+	}
+
+	if (ctx.base == CXL_RESOURCE_NONE) {
+		dev_warn(dev, "CHBS invalid for Host Bridge (UID %lld)\n",
+			 ctx.uid);
+		return false;
+	}
+
+	if ((ctx.cxl_version == ACPI_CEDT_CHBS_VERSION_CXL11 &&
+	     ctx.length != ACPI_CEDT_CHBS_LENGTH_CXL11) ||
+	    (ctx.cxl_version == ACPI_CEDT_CHBS_VERSION_CXL20 &&
+	     ctx.length != ACPI_CEDT_CHBS_LENGTH_CXL20)) {
+		dev_warn(dev, "Invalid length for Host Bridge (UID %lld)\n",
+			 ctx.uid);
+		return false;
+	}
+
+	return true;
+}
+
 static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
 			     const unsigned long end)
 {
@@ -478,10 +503,6 @@ static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
 
 	chbs = (struct acpi_cedt_chbs *) header;
 
-	if (chbs->cxl_version == ACPI_CEDT_CHBS_VERSION_CXL11 &&
-	    chbs->length != CXL_RCRB_SIZE)
-		return 0;
-
 	if (!chbs->base)
 		return 0;
 
@@ -502,6 +523,7 @@ static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
 
 	ctx->cxl_version = chbs->cxl_version;
 	ctx->base = chbs->base;
+	ctx->length = chbs->length;
 
 	return 0;
 }
@@ -570,17 +592,8 @@ static int add_host_bridge_dport(struct device *match, void *arg)
 	if (rc)
 		return rc;
 
-	if (ctx.cxl_version == UINT_MAX) {
-		dev_warn(match, "No CHBS found for Host Bridge (UID %lld)\n",
-			 ctx.uid);
-		return 0;
-	}
-
-	if (ctx.base == CXL_RESOURCE_NONE) {
-		dev_warn(match, "CHBS invalid for Host Bridge (UID %lld)\n",
-			 ctx.uid);
+	if (!cxl_chbs_verify(match, ctx))
 		return 0;
-	}
 
 	pci_root = acpi_pci_find_root(hb->handle);
 	bridge = pci_root->bus->bridge;
-- 
2.47.0

Li Zhijian wrote:
> Per CXL Spec r3.1 Table 9-21, both CXL1.1 and CXL2.0 have defined their
> own length, verify it to avoid an invalid CHBS


I think this looks fine.  But did a platform have issues with this?  Does
this need to be backported?

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

[snip]

On 27/03/2025 11:44, Ira Weiny wrote:
> Li Zhijian wrote:
>> Per CXL Spec r3.1 Table 9-21, both CXL1.1 and CXL2.0 have defined their
>> own length, verify it to avoid an invalid CHBS
> 
> 
> I think this looks fine.  But did a platform have issues with this?  

Not really, actually, I discovered it while reviewing the code and
CXL specification.

Currently, this issue arises only when I inject an incorrect length
via QEMU environment. Our hardware does not experience this problem.


> Does this need to be backported?
I remain neutral :)

Thanks



> 
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> 
> [snip]

Zhijian Li (Fujitsu) wrote:
> 
> 
> On 27/03/2025 11:44, Ira Weiny wrote:
> > Li Zhijian wrote:
> >> Per CXL Spec r3.1 Table 9-21, both CXL1.1 and CXL2.0 have defined their
> >> own length, verify it to avoid an invalid CHBS
> > 
> > 
> > I think this looks fine.  But did a platform have issues with this?  
> 
> Not really, actually, I discovered it while reviewing the code and
> CXL specification.
> 
> Currently, this issue arises only when I inject an incorrect length
> via QEMU environment. Our hardware does not experience this problem.
> 
> 
> > Does this need to be backported?
> I remain neutral :)

What does the kernel do with this invalid CHBS from QEMU? I would be
happy to let whatever bad effect from injecting a corrupted CHBS just
happen because there are plenty of ways for QEMU to confuse the kernel
even if the table lengths are correct.

Unless it has real impact I would rather not touch the kernel for every
possible way that QEMU can make a mistake.

I.e. if it was a widespread problem that affected multiple QEMU users by
default then maybe. Just your local test gone awry? Maybe not.