Messages in this thread | | | Date | Wed, 9 Mar 2016 21:46:12 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v3 07/19] x86, kaslr: Get correct max_addr for relocs pointer |
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On 03/08/16 at 10:16am, Kees Cook wrote: > On Mon, Mar 7, 2016 at 9:13 PM, Baoquan He <bhe@redhat.com> wrote: > > On 03/07/16 at 03:16pm, Kees Cook wrote: > >> On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@redhat.com> wrote: > >> > From: Yinghai Lu <yinghai@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. > > ******************** > > I would say: > > Relocation handling performs bounds checking on the relocated > addresses. The existing code uses output_len (VO size plus relocs > size) as the max address. This is not right since the max_addr check > should stop at the end of VO and exclude bss, brk, etc, which follows. > The valid range should be VO [_text, __bss_start] in the loaded > physical address space. > > In this patch, add export for __bss_start to voffset.h and use it to > get the correct max_addr.
Yeah, it's much better. Will use this as patch log.
Thanks!
> > > Thanks! > > -Kees > > > > >> > > >> > In the patch, add export for __bss_start to voffset.h and use it to get > >> > max_addr. > >> > > >> > Signed-off-by: Yinghai Lu <yinghai@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 > > > > -- > Kees Cook > Chrome OS & Brillo Security
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