Tables: Do not validate signature for dynamic table load

Windows seems to allow arbitrary table signatures for Load/LoadTable
opcodes:
  ACPI BIOS Error (bug): Table has invalid signature [PRAD] (0x44415250)
So this patch removes dynamic load signature checks. However we need to
find a way to avoid table loading against tables like MADT. This is not
covered by this commit.

This Windows behavior has been validated on link #1. An end user bug
report can also be found on link #2.

This patch also includes simple cleanup for static load signature check
code. Reported by Ye Xiaolong, Fixed by Lv Zheng.

Link: #121 [#1]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=118601 [#2]
Reported-by: Ye Xiaolong <xiaolong.ye@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>

source/components/tables/tbinstal.c

@@ -351,32 +351,6 @@ AcpiTbInstallStandardTable (
 
     if (Reload)
     {
-        /*
-         * Validate the incoming table signature.
-         *
-         * 1) Originally, we checked the table signature for "SSDT" or "PSDT".
-         * 2) We added support for OEMx tables, signature "OEM".
-         * 3) Valid tables were encountered with a null signature, so we just
-         *    gave up on validating the signature, (05/2008).
-         * 4) We encountered non-AML tables such as the MADT, which caused
-         *    interpreter errors and kernel faults. So now, we once again allow
-         *    only "SSDT", "OEMx", and now, also a null signature. (05/2011).
-         */
-        if ((NewTableDesc.Signature.Ascii[0] != 0x00) &&
-           (!ACPI_COMPARE_NAME (&NewTableDesc.Signature, ACPI_SIG_SSDT)) &&
-           (strncmp (NewTableDesc.Signature.Ascii, "OEM", 3)))
-        {
-            ACPI_BIOS_ERROR ((AE_INFO,
-                "Table has invalid signature [%4.4s] (0x%8.8X), "
-                "must be SSDT or OEMx",
-                AcpiUtValidNameseg (NewTableDesc.Signature.Ascii) ?
-                    NewTableDesc.Signature.Ascii : "????",
-                NewTableDesc.Signature.Integer));
-
-            Status = AE_BAD_SIGNATURE;
-            goto UnlockAndExit;
-        }
-
         /* Check if table is already registered */
 
         for (i = 0; i < AcpiGbl_RootTableList.CurrentTableCount; ++i)

source/components/tables/tbxfload.c

@@ -336,11 +336,11 @@ AcpiTbLoadNamespace (
     {
         Table = &AcpiGbl_RootTableList.Tables[i];
 
-        if (!AcpiGbl_RootTableList.Tables[i].Address ||
+        if (!Table->Address ||
             (!ACPI_COMPARE_NAME (Table->Signature.Ascii, ACPI_SIG_SSDT) &&
              !ACPI_COMPARE_NAME (Table->Signature.Ascii, ACPI_SIG_PSDT) &&
              !ACPI_COMPARE_NAME (Table->Signature.Ascii, ACPI_SIG_OSDT)) ||
-             ACPI_FAILURE (AcpiTbValidateTable (Table)))
+            ACPI_FAILURE (AcpiTbValidateTable (Table)))
         {
             continue;
         }