Messages in this thread | | | Date | Tue, 9 Sep 2014 08:53:29 -0700 | Subject | Re: [PATCH 1/4] kaslr: check user's config too when handle relocations | From | Kees Cook <> |
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On Mon, Sep 8, 2014 at 11:24 PM, Baoquan He <bhe@redhat.com> wrote: > On 09/05/14 at 10:11am, Kees Cook wrote: >> I don't think this is correct. If you look at a02150610776 ("x86, >> relocs: Move ELF relocation handling to C"), we always did relocations >> on 32-bit when CONFIG_RELOCATABLE was set, so I think this will fail >> badly on 32-bit. 64-bit only needs relocation when >> CONFIG_RANDOMIZE_BASE is set, so this is probably what needs to be >> tested here instead. I think a better option would be, in >> decompress_kernel(), to compare output before and after >> choose_kernel_location(). If it's the same on 64-bit, >> handle_relocations() can be skipped. (Perhaps pass the before/after to >> handle_relocations() and it can perform the logic.) >> >> -Kees > > Hi Kees, > > Checking handle_relocations() again, I just didn't notice it's mandatory > to do the relocations handling in i386. So in this function delta is > checked to see if it's a kaslr relocation handling. This might be a > little confusing. But I am fine with it. > > Per your comment, you prefer to compare the output before and after > choose_kernel_location(). That's also good, Lu Yinghai posted a draft > patch in this way before, however the checking and the delta calculation > are not correct. I changed that and test all cases, it works well. So > do you like this it? If yes I will repost it. > > From 13471bd838c52a0e143c2aee81e3863cfff585bd Mon Sep 17 00:00:00 2001 > From: Baoquan He <bhe@redhat.com> > Date: Mon, 25 Aug 2014 14:57:43 +0800 > Subject: [PATCH] kaslr: check if kernel location is changed > > Signed-off-by: Baoquan He <bhe@redhat.com> > --- > arch/x86/boot/compressed/misc.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c > index 57ab74d..887f404 100644 > --- a/arch/x86/boot/compressed/misc.c > +++ b/arch/x86/boot/compressed/misc.c > @@ -230,8 +230,9 @@ static void error(char *x) > asm("hlt"); > } > > -#if CONFIG_X86_NEED_RELOCS > -static void handle_relocations(void *output, unsigned long output_len) > +#ifdef CONFIG_X86_NEED_RELOCS > +static void handle_relocations(void *output_orig, void *output, > + unsigned long output_len) > { > int *reloc; > unsigned long delta, map, ptr; > @@ -242,6 +243,9 @@ static void handle_relocations(void *output, unsigned long output_len) > * Calculate the delta between where vmlinux was linked to load > * and where it was actually loaded. > */ > + if (output_orig == output) > + return; > +
I still think this needs a test for the 32-bit case, since IUIC, it requires relocations unconditionally.
-Kees
> delta = min_addr - LOAD_PHYSICAL_ADDR; > if (!delta) { > debug_putstr("No relocation needed... "); > @@ -299,7 +303,8 @@ static void handle_relocations(void *output, unsigned long output_len) > #endif > } > #else > -static inline void handle_relocations(void *output, unsigned long output_len) > +static inline void handle_relocations(void *output_orig, void *output, > + unsigned long output_len) > { } > #endif > > @@ -360,6 +365,8 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap, > unsigned char *output, > unsigned long output_len) > { > + unsigned char *output_orig = output; > + > real_mode = rmode; > > sanitize_boot_params(real_mode); > @@ -402,7 +409,7 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap, > debug_putstr("\nDecompressing Linux... "); > decompress(input_data, input_len, NULL, NULL, output, NULL, error); > parse_elf(output); > - handle_relocations(output, output_len); > + handle_relocations(output_orig, output, output_len); > debug_putstr("done.\nBooting the kernel.\n"); > return output; > } > -- > 1.8.5.3 >
-- Kees Cook Chrome OS Security
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