iPXE boot to Windows writing back to boot device

[mcb30]

(2014-03-11 05:55)mdevey Wrote:  wimboot/src/int.c

Code:

//other int 13h codes that looked vaguely write'ish
                case 0x0b:
                case 0x03:
                case 0x05:
                case 0x06:
                case 0x07:
                case 0x45:
                case INT13_EXTENDED_WRITE:
                        int13_extended_write ( params );
                        break;

Verified I used a modified wimboot by altering read to fail, and window gives a nice error message.

ipxe/win7 combo may just expose a bug in our system. Would welcome any suggested parts of ipxe I could alter to help track it down?

If you're happy hacking around in the wimboot code, then I would suggest trying to intercept (and ignore) writes to INT 13 drives other than the vdisk emulated drive: see the "Pass through command to underlying INT 13" section in emulate_int13(). Note that you can't just refuse to pass through all INT 13 calls, since some are not drive-number-specific.

It should be relatively straightforward to establish whether or not the write is coming via the INT 13 interface, and to block it if so.

If you do find a hack that works, please let me know so that we can work it up into a full solution and publish a new version of wimboot.

Michael