* Dov Murik ([email protected]) wrote:
> When pc_system_parse_ovmf_flash() parses the optional GUIDed table in
> the end of the OVMF flash memory area, the table length field is checked
> for sizes that are too small, but doesn't error on sizes that are too
> big (bigger than the flash content itself).
>
> Add a check for maximal size of the OVMF table, and add an error report
> in case the size is invalid. In such a case, an error like this will be
> displayed during launch:
>
> qemu-system-x86_64: OVMF table has invalid size 4047
>
> and the table parsing is skipped.
>
> Signed-off-by: Dov Murik <[email protected]>
>
> ---
>
> v2:
> - add error message example to commit description
> - replace magic numbers 48 and 50 with size calculations (thanks Phil MD)
> ---
> hw/i386/pc_sysfw_ovmf.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/hw/i386/pc_sysfw_ovmf.c b/hw/i386/pc_sysfw_ovmf.c
> index f4dd92c588..1c9a16e9e6 100644
> --- a/hw/i386/pc_sysfw_ovmf.c
> +++ b/hw/i386/pc_sysfw_ovmf.c
> @@ -24,11 +24,14 @@
> */
>
> #include "qemu/osdep.h"
> +#include "qemu/error-report.h"
> #include "hw/i386/pc.h"
> #include "cpu.h"
>
> #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;
> @@ -38,6 +41,8 @@ void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t
> flash_size)
> uint8_t *ptr;
> QemuUUID guid;
> int tot_len;
> + int max_tot_len = flash_size - (bytes_after_table_footer +
> + sizeof(guid) + sizeof(uint16_t));
>
> /* should only be called once */
> if (ovmf_flash_parsed) {
> @@ -52,12 +57,13 @@ 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;
> }
> @@ -66,7 +72,13 @@ void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t
> flash_size)
> ptr -= sizeof(uint16_t);
> tot_len = le16_to_cpu(*(uint16_t *)ptr) - sizeof(guid) -
> sizeof(uint16_t);
Instead of the max_tot_len calculation above, is it actually:
max_tot_len = ptr - flash_ptr;
I think that works out the same and avoids doing the calculation in two
places; it's also logically what you have - you can't read over the
structure you just read.
Dave
> - if (tot_len <= 0) {
> + if (tot_len < 0 || tot_len > max_tot_len) {
> + error_report("OVMF table has invalid size %d", tot_len);
> + return;
> + }
> +
> + if (tot_len == 0) {
> + /* no entries in the OVMF table */
> return;
> }
>
>
> base-commit: 48033ad678ae2def43bf0d543a2c4c3d2a93feaf
> --
> 2.25.1
>
--
Dr. David Alan Gilbert / [email protected] / Manchester, UK
