Messages in this thread | | | Date | Fri, 05 Dec 2014 11:06:44 -0800 | From | David Daney <> | Subject | Re: [PATCH v3 3/3] MIPS: set stack/data protection as non-executable |
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On 12/05/2014 10:51 AM, Kees Cook wrote: > On Fri, Dec 5, 2014 at 9:28 AM, David Daney <ddaney.cavm@gmail.com> wrote: >> On 12/02/2014 05:58 PM, Leonid Yegoshin wrote: >>> >>> This is a last step of 3 patches which shift FPU emulation out of >>> stack into protected area. So, it disables a default executable stack. >>> >>> Additionally, it sets a default data area non-executable protection. >>> >>> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> >> >> >> NAK! >> >> Some programs require an executable stack, this patch will break them. > > Have you tested this?
Do you require empirical evidence that the patch is incorrect, or is it enough to just to trust me when I say that it is incorrect? Typically the burden of proof is with those proposing the patches.
> >> You can only select a non-executable stack in response to PT_GNU_STACK >> program headers in the ELF file of the executable program. > > This is already handled by fs/binfmt_elf.c. It does the parsing of the > PT_GNU_STACK needs, and sets up the stack flags appropriately. All the > change to VM_DATA_DEFAULT_FLAGS does is make sure that EXSTACK_DEFAULT > now means no VM_EXEC by default. If PT_GNU_STACK requires it, it gets > added back in. >
The problem is not with "modern" executables that are properly annotated with PT_GNU_STACK.
My objection is to the intentional breaking of old executables that have no PT_GNU_STACK annotation, but require an executable stack. Since we usually try not to break userspace, we cannot merge a patch like this one.
David Daney.
> -Kees > >> >> David Daney >> >> >> >>> --- >>> arch/mips/include/asm/page.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h >>> index 3be81803595d..d49ba81cb4ed 100644 >>> --- a/arch/mips/include/asm/page.h >>> +++ b/arch/mips/include/asm/page.h >>> @@ -230,7 +230,7 @@ extern int __virt_addr_valid(const volatile void >>> *kaddr); >>> #define virt_addr_valid(kaddr) >>> \ >>> __virt_addr_valid((const volatile void *) (kaddr)) >>> >>> -#define VM_DATA_DEFAULT_FLAGS (VM_READ | VM_WRITE | VM_EXEC | \ >>> +#define VM_DATA_DEFAULT_FLAGS (VM_READ | VM_WRITE | \ >>> VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC) >>> >>> #define UNCAC_ADDR(addr) ((addr) - PAGE_OFFSET + UNCAC_BASE) >>> >>> >>> >>> >> > > >
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