[v3,2/2] hw/i386: Replace magic number with field length calculation

Commit Message

Dov Murik Feb. 22, 2022, 7:19 a.m. UTC

Replce the literal magic number 48 with length calculation (32 bytes at
the end of the firmware after the table footer + 16 bytes of the OVMF
table footer GUID).

No functional change intended.

Signed-off-by: Dov Murik <[e-mail]>
---
 hw/i386/pc_sysfw_ovmf.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Comments

Daniel P. Berrangé Feb. 22, 2022, 9:25 a.m. UTC | #1

On Tue, Feb 22, 2022 at 07:19:06AM +0000, Dov Murik wrote:
> Replce the literal magic number 48 with length calculation (32 bytes at
> the end of the firmware after the table footer + 16 bytes of the OVMF
> table footer GUID).
> 
> No functional change intended.
> 
> Signed-off-by: Dov Murik <[e-mail]>
> ---
>  hw/i386/pc_sysfw_ovmf.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Reviewed-by: Daniel P. Berrangé <[e-mail]>


Regards,
Daniel

Patch

diff --git a/hw/i386/pc_sysfw_ovmf.c b/hw/i386/pc_sysfw_ovmf.c
index df15c9737b..07a4c267fa 100644
--- a/hw/i386/pc_sysfw_ovmf.c
+++ b/hw/i386/pc_sysfw_ovmf.c
@@ -30,6 +30,8 @@ 
 
 #define OVMF_TABLE_FOOTER_GUID "96b582de-1fb2-45f7-baea-a366c55a082d"
 
+static const int bytes_after_table_footer = 32;
+
 static bool ovmf_flash_parsed;
 static uint8_t *ovmf_table;
 static int ovmf_table_len;
@@ -53,12 +55,13 @@  void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t flash_size)
 
     /*
      * if this is OVMF there will be a table footer
-     * guid 48 bytes before the end of the flash file.  If it's
-     * not found, silently abort the flash parsing.
+     * guid 48 bytes before the end of the flash file
+     * (= 32 bytes after the table + 16 bytes the GUID itself).
+     * If it's not found, silently abort the flash parsing.
      */
     qemu_uuid_parse(OVMF_TABLE_FOOTER_GUID, &guid);
     guid = qemu_uuid_bswap(guid); /* guids are LE */
-    ptr = flash_ptr + flash_size - 48;
+    ptr = flash_ptr + flash_size - (bytes_after_table_footer + sizeof(guid));
     if (!qemu_uuid_is_equal((QemuUUID *)ptr, &guid)) {
         return;
     }