4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> commit 04a848106193b134741672f7e4e444b50c70b631 upstream. As reported by Zijun, the fdt_check_header() call in __fixmap_remap_fdt() is not safe since it is not guaranteed that the FDT header is mapped completely. Due to the minimum alignment of 8 bytes, the only fields we can assume to be mapped are 'magic' and 'totalsize'. Since the OF layer is in charge of validating the FDT image, and we are only interested in making reasonably sure that the size field contains a meaningful value, replace the fdt_check_header() call with an explicit comparison of the magic field's value against the expected value. Reported-by: Zijun Hu <zijun_hu@xxxxxxx> Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Signed-off-by: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/mm/mmu.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -652,9 +652,9 @@ void *__init fixmap_remap_fdt(phys_addr_ /* * Check whether the physical FDT address is set and meets the minimum * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be - * at least 8 bytes so that we can always access the size field of the - * FDT header after mapping the first chunk, double check here if that - * is indeed the case. + * at least 8 bytes so that we can always access the magic and size + * fields of the FDT header after mapping the first chunk, double check + * here if that is indeed the case. */ BUILD_BUG_ON(MIN_FDT_ALIGN < 8); if (!dt_phys || dt_phys % MIN_FDT_ALIGN) @@ -682,7 +682,7 @@ void *__init fixmap_remap_fdt(phys_addr_ create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base, SWAPPER_BLOCK_SIZE, prot); - if (fdt_check_header(dt_virt) != 0) + if (fdt_magic(dt_virt) != FDT_MAGIC) return NULL; size = fdt_totalsize(dt_virt); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html