>>> On 3/30/2015 at 10:02 PM, Kevin O'Connor <ke...@koconnor.net> wrote: > On Mon, Mar 30, 2015 at 05:06:30PM -0600, Bruce Rogers wrote: >> The SMBIOS anchor string _SM_ is stored within SeaBIOS to validate >> an SMBIOS entry point structure. There is the possibility (observed) >> that this comparison string ends up paragraph aligned and mistakenly >> found during a search for the real SMBIOS entry point. Ensure it will >> never end up on a paragraph boundary by storing it at odd alignment. > > Thanks. > > What OS was this on? It's really an OS bug as the OS needs to check > both the signature and the checksum. > > My preferred approach to addressing this would be to turn > p->anchor_string into a u32 and do an integer compare instead of a > string compare. Although technically this can lead to the same > potential issue, in practice it should not happen because SeaBIOS' > init code is relocated out of the f-segment during startup (while > static strings are generally not). > > -Kevin
This was actually flagged by the QEMU make check test in tests/bios-tables-test.c, where the code has asserts based on the first find of the _SM_ string found on a paragraph boundary in the f segment. It assumes that the string found is sufficient to identify the smbios entry point structure. I read in http://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.0.0.pdf where there are number of steps needed to verify the entry-point, beyond finding the anchor string. So I assume that the make check test needs to be fixed. But I wonder if bios creators are also supposed to ensure that there is no such string findable on a paragraph boundary so as to avoid any potential confusion? I don't have expereince writing bios's so I am only guessing at that. Bruce