Re: [Qemu-devel] [PATCH v3] bios-tables-test: handle false-positive smbios signature matches

[Gabriel L. Somlo]

ping ?

On Mon, May 18, 2015 at 08:47:24AM -0400, 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 within 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 <address@hidden>
> Signed-off-by: Gabriel Somlo <address@hidden>
> Tested-by: Bruce Rogers <address@hidden>
> ---
> 
>  - Added motivation for patch in commit log, as requested by mst
>    (whom I forgot to cc on v2 -- D'OH!!! ) :)
> 
>  - Fixed s/withing/within/ as pointed out by eblake
> 
> Thanks,
>   Gabriel
> 
>  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 7e85dc4..0de1742 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
>