ACPI: fix APEI related table size checking

On Huang Ying's machine:

erst_tab->header_length == sizeof(struct acpi_table_einj)

but Yinghai reported that on his machine,

erst_tab->header_length == sizeof(struct acpi_table_einj) -
sizeof(struct acpi_table_header)

To make erst table size checking code works on all systems, both
testing are treated as PASS.

Same situation applies to einj_tab->header_length, so corresponding
table size checking is changed in similar way too.

Originally-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Huang Ying <ying.huang@intel.com>

- use switch() for better readability
- add comment explaining why a formally invalid size it also being
  accepted
- check erst_tab->header.length before even looking at
  erst_tab->header_length
- prefer sizeof(*erst_tab) over sizeof(struct acpi_table_erst)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
master commit: 915ef37d7cc8fcac5b37eb0b40c693754fcd12ab
master date: 2012-10-16 17:26:36 +0200

1 files changed, 14 insertions, 3 deletions

diff --git a/xen/drivers/acpi/apei/erst.c b/xen/drivers/acpi/apei/erst.c
index 1e420c5203..71db9fa5a4 100644
--- a/xen/drivers/acpi/apei/erst.c
+++ b/xen/drivers/acpi/apei/erst.c
@@ -764,12 +764,23 @@ int erst_clear(u64 record_id)
 
 static int __init erst_check_table(struct acpi_table_erst *erst_tab)
 {
-	if (erst_tab->header_length != sizeof(struct acpi_table_erst))
+	if (erst_tab->header.length < sizeof(*erst_tab))
 		return -EINVAL;
-	if (erst_tab->header.length < sizeof(struct acpi_table_erst))
+
+	switch (erst_tab->header_length) {
+	case sizeof(*erst_tab) - sizeof(erst_tab->header):
+	/*
+	 * While invalid per specification, there are (early?) systems
+	 * indicating the full header size here, so accept that value too.
+	 */
+	case sizeof(*erst_tab):
+		break;
+	default:
 		return -EINVAL;
+	}
+
 	if (erst_tab->entries !=
-	    (erst_tab->header.length - sizeof(struct acpi_table_erst)) /
+	    (erst_tab->header.length - sizeof(*erst_tab)) /
 	    sizeof(struct acpi_erst_entry))
 		return -EINVAL;