hw/elf_ops: defend against weird elf headers

According to the ELF spec: PT_LOAD The array element specifies a loadable segment, described by p_filesz and p_memsz. The bytes from the file are mapped to the beginning of the memory segment. If the segment's memory size (p_memsz) is larger than the file size (p_filesz), the ``extra'' bytes are defined to hold the value 0 and to follow the segment's initialized area. The file size may not be larger than the memory size. Loadable segment entries in the program header table appear in ascending order, sorted on the p_vaddr member. which implies while both p_filesz and p_memsz can be zero we should never see a case where p_filesz is greater than the in memory size. Indeed it has been reported such a hand crafted ELF can blow up, for example during rom_reset(): address_space_set(rom->as, rom->addr + rom->datasize, 0, rom->romsize - rom->datasize, MEMTXATTRS_UNSPECIFIED); which could trigger and underflow leaving QEMU slowly filling a very large buffer. Cc: qemu-stable@nongnu.org Fixes: https://gitlab.com/qemu-project/qemu/-/work_items/4056 Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com> Message-ID: <20260812081405.3811787-1-alex.bennee@linaro.org> Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>