On 03/07/16 at 03:16pm, Kees Cook wrote: > On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <b...@redhat.com> wrote: > > From: Yinghai Lu <ying...@kernel.org> > > > > There is boundary checking for pointer in kaslr relocation handling. > > > > Current code is using output_len, and that is VO (vmlinux after objcopy) > > file size plus vmlinux.relocs file size. > > > > That is not right, as we should use loaded address for running. > > I think this needs clarification. If I'm understanding correctly, the > max_addr check should stop at the end of VO, and not include bss, brk, > etc. which follows. In which case, this change is correct: the bounds > checking needed to be tightened.
Yes, exactly as you means. > > > > > > At that time parse_elf already move the sections according to ELF headers. > > > > The valid range should be VO [_text, __bss_start) loaded physical addresses. I think it is expressed here. Maybe we can stress it in this patch log. After all it's the main idea of this patch. How about rewriting patch log like this: ******************** There is boundary checking for pointer in kaslr relocation handling. However current code is using output_len that is VO (vmlinux after objcopy) file size plus vmlinux.relocs file size to make the valid boundary. That is not right since the max_addr check should stop at the end of VO and excludes bss, brk etc, which follows. Means the valid range should be VO [_text, __bss_start] in loaded physical address space. In this patch, add export for __bss_start to voffset.h and use it to get max_addr. ******************** > > > > In the patch, add export for __bss_start to voffset.h and use it to get > > max_addr. > > > > Signed-off-by: Yinghai Lu <ying...@kernel.org> > > --- > > v2->v3: > > Tune the patch log. > > > > arch/x86/boot/compressed/Makefile | 2 +- > > arch/x86/boot/compressed/misc.c | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/Makefile > > b/arch/x86/boot/compressed/Makefile > > index fef80fa..2e7c0ce 100644 > > --- a/arch/x86/boot/compressed/Makefile > > +++ b/arch/x86/boot/compressed/Makefile > > @@ -41,7 +41,7 @@ LDFLAGS_vmlinux := -T > > hostprogs-y := mkpiggy > > HOST_EXTRACFLAGS += -I$(srctree)/tools/include > > > > -sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] > > \(_text\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p' > > +sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] > > \(_text\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p' > > > > quiet_cmd_voffset = VOFFSET $@ > > cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@ > > diff --git a/arch/x86/boot/compressed/misc.c > > b/arch/x86/boot/compressed/misc.c > > index 069120e..dd7ed8a 100644 > > --- a/arch/x86/boot/compressed/misc.c > > +++ b/arch/x86/boot/compressed/misc.c > > @@ -259,7 +259,7 @@ static void handle_relocations(void *output, unsigned > > long output_len) > > int *reloc; > > unsigned long delta, map, ptr; > > unsigned long min_addr = (unsigned long)output; > > - unsigned long max_addr = min_addr + output_len; > > + unsigned long max_addr = min_addr + (VO___bss_start - VO__text); > > > > /* > > * Calculate the delta between where vmlinux was linked to load > > -- > > 2.5.0 > > > > > > -- > Kees Cook > Chrome OS & Brillo Security
