[Qemu-devel] [PATCH v2] bios-tables-test: handle false-positive smbios signature matches

[Qemu-devel] [PATCH v2] bios-tables-test: handle false-positive smbios signature matches

[Gabriel L. Somlo]

It has been reported that sometimes the .rodata section of SeaBIOS,
containing the constant string against which the SMBIOS signature
ends up being compared, also falls withing the guest f-segment. In
that case, the test obviously fails, unless we continue searching
for the *real* smbios entry point.

Rather than stopping at the first match for the SMBIOS signature
("_SM_") in the f-segment (0xF0000-0xFFFFF), continue scanning
until either a valid entry point table is found, or the f-segment
has been exhausted.

Reported-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Tested-by: Bruce Rogers <brogers@suse.com>
---
 tests/bios-tables-test.c | 76 ++++++++++++++++++++++++++++--------------------
 1 file changed, 44 insertions(+), 32 deletions(-)

diff --git a/tests/bios-tables-test.c b/tests/bios-tables-test.c
index 735ac61..f79d89a 100644
--- a/tests/bios-tables-test.c
+++ b/tests/bios-tables-test.c
@@ -599,35 +599,15 @@ static void test_acpi_asl(test_data *data)
     free_test_data(&exp_data);
 }
 
-static void test_smbios_ep_address(test_data *data)
-{
-    uint32_t off;
-
-    /* find smbios entry point structure */
-    for (off = 0xf0000; off < 0x100000; off += 0x10) {
-        uint8_t sig[] = "_SM_";
-        int i;
-
-        for (i = 0; i < sizeof sig - 1; ++i) {
-            sig[i] = readb(off + i);
-        }
-
-        if (!memcmp(sig, "_SM_", sizeof sig)) {
-            break;
-        }
-    }
-
-    g_assert_cmphex(off, <, 0x100000);
-    data->smbios_ep_addr = off;
-}
-
-static void test_smbios_ep_table(test_data *data)
+static bool smbios_ep_table_ok(test_data *data)
 {
     struct smbios_entry_point *ep_table = &data->smbios_ep_table;
     uint32_t addr = data->smbios_ep_addr;
 
     ACPI_READ_ARRAY(ep_table->anchor_string, addr);
-    g_assert(!memcmp(ep_table->anchor_string, "_SM_", 4));
+    if (memcmp(ep_table->anchor_string, "_SM_", 4)) {
+        return false;
+    }
     ACPI_READ_FIELD(ep_table->checksum, addr);
     ACPI_READ_FIELD(ep_table->length, addr);
     ACPI_READ_FIELD(ep_table->smbios_major_version, addr);
@@ -636,17 +616,50 @@ static void test_smbios_ep_table(test_data *data)
     ACPI_READ_FIELD(ep_table->entry_point_revision, addr);
     ACPI_READ_ARRAY(ep_table->formatted_area, addr);
     ACPI_READ_ARRAY(ep_table->intermediate_anchor_string, addr);
-    g_assert(!memcmp(ep_table->intermediate_anchor_string, "_DMI_", 5));
+    if (memcmp(ep_table->intermediate_anchor_string, "_DMI_", 5)) {
+        return false;
+    }
     ACPI_READ_FIELD(ep_table->intermediate_checksum, addr);
     ACPI_READ_FIELD(ep_table->structure_table_length, addr);
-    g_assert_cmpuint(ep_table->structure_table_length, >, 0);
+    if (ep_table->structure_table_length == 0) {
+        return false;
+    }
     ACPI_READ_FIELD(ep_table->structure_table_address, addr);
     ACPI_READ_FIELD(ep_table->number_of_structures, addr);
-    g_assert_cmpuint(ep_table->number_of_structures, >, 0);
+    if (ep_table->number_of_structures == 0) {
+        return false;
+    }
     ACPI_READ_FIELD(ep_table->smbios_bcd_revision, addr);
-    g_assert(!acpi_checksum((uint8_t *)ep_table, sizeof *ep_table));
-    g_assert(!acpi_checksum((uint8_t *)ep_table + 0x10,
-                            sizeof *ep_table - 0x10));
+    if (acpi_checksum((uint8_t *)ep_table, sizeof *ep_table) ||
+        acpi_checksum((uint8_t *)ep_table + 0x10, sizeof *ep_table - 0x10)) {
+        return false;
+    }
+    return true;
+}
+
+static void test_smbios_entry_point(test_data *data)
+{
+    uint32_t off;
+
+    /* find smbios entry point structure */
+    for (off = 0xf0000; off < 0x100000; off += 0x10) {
+        uint8_t sig[] = "_SM_";
+        int i;
+
+        for (i = 0; i < sizeof sig - 1; ++i) {
+            sig[i] = readb(off + i);
+        }
+
+        if (!memcmp(sig, "_SM_", sizeof sig)) {
+            /* signature match, but is this a valid entry point? */
+            data->smbios_ep_addr = off;
+            if (smbios_ep_table_ok(data)) {
+                break;
+            }
+        }
+    }
+
+    g_assert_cmphex(off, <, 0x100000);
 }
 
 static inline bool smbios_single_instance(uint8_t type)
@@ -767,8 +780,7 @@ static void test_acpi_one(const char *params, test_data *data)
         }
     }
 
-    test_smbios_ep_address(data);
-    test_smbios_ep_table(data);
+    test_smbios_entry_point(data);
     test_smbios_structs(data);
 
     qtest_quit(global_qtest);
-- 
2.1.0

Re: [Qemu-devel] [PATCH v2] bios-tables-test: handle false-positive smbios signature matches

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1024 bytes --]

On 04/28/2015 01:55 PM, Gabriel L. Somlo wrote:
> It has been reported that sometimes the .rodata section of SeaBIOS,
> containing the constant string against which the SMBIOS signature
> ends up being compared, also falls withing the guest f-segment. In

s/withing/within/

> that case, the test obviously fails, unless we continue searching
> for the *real* smbios entry point.
> 
> Rather than stopping at the first match for the SMBIOS signature
> ("_SM_") in the f-segment (0xF0000-0xFFFFF), continue scanning
> until either a valid entry point table is found, or the f-segment
> has been exhausted.
> 
> Reported-by: Bruce Rogers <brogers@suse.com>
> Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
> Tested-by: Bruce Rogers <brogers@suse.com>
> ---
>  tests/bios-tables-test.c | 76 ++++++++++++++++++++++++++++--------------------
>  1 file changed, 44 insertions(+), 32 deletions(-)
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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