Re: [Qemu-devel] [PATCH QEMU v1 1/4] multiboot: bss_end_addr can be zero

[P J P]

+-- On Thu, 21 Dec 2017, Jack Schwartz wrote --+
| The multiboot spec (https://www.gnu.org/software/grub/manual/multiboot/),
| section 3.1.3, allows for bss_end_addr to be zero.
| 
| A zero bss_end_addr signifies there is no .bss section.
| 
| Suggested-by: Daniel Kiper <address@hidden>
| Signed-off-by: Jack Schwartz <address@hidden>
| Reviewed-by: Daniel Kiper <address@hidden>
| ---
|  hw/i386/multiboot.c | 18 ++++++++++--------
|  1 file changed, 10 insertions(+), 8 deletions(-)
| 
| diff --git a/hw/i386/multiboot.c b/hw/i386/multiboot.c
| index c7b70c9..ff2733d 100644
| --- a/hw/i386/multiboot.c
| +++ b/hw/i386/multiboot.c
| @@ -233,12 +233,6 @@ int load_multiboot(FWCfgState *fw_cfg,
|          mh_entry_addr = ldl_p(header+i+28);
|  
|          if (mh_load_end_addr) {
| -            if (mh_bss_end_addr < mh_load_addr) {
| -                fprintf(stderr, "invalid mh_bss_end_addr address\n");
| -                exit(1);
| -            }
| -            mb_kernel_size = mh_bss_end_addr - mh_load_addr;
| -
|              if (mh_load_end_addr < mh_load_addr) {
|                  fprintf(stderr, "invalid mh_load_end_addr address\n");
|                  exit(1);
| @@ -249,8 +243,16 @@ int load_multiboot(FWCfgState *fw_cfg,
|                  fprintf(stderr, "invalid kernel_file_size\n");
|                  exit(1);
|              }
| -            mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
| -            mb_load_size = mb_kernel_size;
| +            mb_load_size = kernel_file_size - mb_kernel_text_offset;
| +        }
| +        if (mh_bss_end_addr) {
| +            if (mh_bss_end_addr < (mh_load_addr + mb_load_size)) {
| +                fprintf(stderr, "invalid mh_bss_end_addr address\n");
| +                exit(1);
| +            }
| +            mb_kernel_size = mh_bss_end_addr - mh_load_addr;
| +        } else {
| +            mb_kernel_size = mb_load_size;
|          }
|  
|          /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.

Looks good.
Reviewed-by: Prasad J Pandit <address@hidden>

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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