| Message ID | CAKv+Gu_L-9bnaDs-HAONgHARFpeEk41y0KUAFobBcdh1i9Ughg@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 7 December 2015 at 23:14, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 7 December 2015 at 22:56, Kees Cook <keescook@chromium.org> wrote: >> On Mon, Dec 7, 2015 at 1:52 PM, Ard Biesheuvel >> <ard.biesheuvel@linaro.org> wrote: >>> On 7 December 2015 at 21:54, Kees Cook <keescook@chromium.org> wrote: >>>> When rodata is large enough that it crosses a section boundary after the >>>> kernel text, mark the rest NX. This is as close to full NX of rodata as >>>> we can get without splitting page tables or doing section alignment via >>>> CONFIG_DEBUG_ALIGN_RODATA. >>>> >>>> Signed-off-by: Kees Cook <keescook@chromium.org> >>>> --- >>>> I am baffled why I can't put the ALIGN in the ".start = " initializer. >>>> GCC seems to think it's non-static, but only because of the "&" operator. >>>> Does anyone see a way to do this that doesn't require the runtime ALIGN? >>> >>> Yes, but you need to move the ALIGN() expression to the linker script >>> as the value of a new symbol >> >> I didn't see a way to do this without actually bumping the alignment >> (CONFIG_DEBUG_ALIGN_RODATA already does that, I want the other case). >> Do you have an example anywhere I could look at? >> > > Something like this (untested) > > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S > index 8b60fde5ce48..9fb98c5dd35b 100644 > --- a/arch/arm/kernel/vmlinux.lds.S > +++ b/arch/arm/kernel/vmlinux.lds.S > @@ -336,6 +336,8 @@ SECTIONS > STABS_DEBUG > } > > +__start_rodata_section_aligned = ALIGN(__start_rodata, 1 << SECTION_SHIFT); > + > /* > * These must never be empty > * If you have to comment these two assert statements out, your > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c > index 8a63b4cdc0f2..ddacd3bd8f8b 100644 > --- a/arch/arm/mm/init.c > +++ b/arch/arm/mm/init.c > @@ -592,15 +592,13 @@ static struct section_perm nx_perms[] = { > .mask = ~PMD_SECT_XN, > .prot = PMD_SECT_XN, > }, > -#ifdef CONFIG_DEBUG_RODATA > /* Make rodata NX (set RO in ro_perms below). */ > { > - .start = (unsigned long)__start_rodata, > + .start = (unsigned long)__start_rodata_section_aligned, > .end = (unsigned long)__init_begin, > .mask = ~PMD_SECT_XN, > .prot = PMD_SECT_XN, > }, > -#endif > }; > > #ifdef CONFIG_DEBUG_RODATA ... and you also need a extern char __start_rodata_section_aligned[]; somewhere; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S index 8b60fde5ce48..9fb98c5dd35b 100644 --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -336,6 +336,8 @@ SECTIONS STABS_DEBUG } +__start_rodata_section_aligned = ALIGN(__start_rodata, 1 << SECTION_SHIFT); + /* * These must never be empty * If you have to comment these two assert statements out, your diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index 8a63b4cdc0f2..ddacd3bd8f8b 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -592,15 +592,13 @@ static struct section_perm nx_perms[] = { .mask = ~PMD_SECT_XN, .prot = PMD_SECT_XN, }, -#ifdef CONFIG_DEBUG_RODATA /* Make rodata NX (set RO in ro_perms below). */ { - .start = (unsigned long)__start_rodata, + .start = (unsigned long)__start_rodata_section_aligned, .end = (unsigned long)__init_begin, .mask = ~PMD_SECT_XN, .prot = PMD_SECT_XN, }, -#endif }; #ifdef CONFIG_DEBUG_RODATA