On Fri, Dec 5, 2014 at 11:06 AM, David Daney <ddaney.cavm@xxxxxxxxx> wrote: > On 12/05/2014 10:51 AM, Kees Cook wrote: >> >> On Fri, Dec 5, 2014 at 9:28 AM, David Daney <ddaney.cavm@xxxxxxxxx> 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@xxxxxxxxxx> >>> >>> >>> >>> 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. My fault, I misunderstood. (See below.) >>> 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. Ah! Okay. If legacy executables expected an executable stack for more reasons than FPU emulation, then yes, absolutely I agree with you. -Kees > > 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) >>>> >>>> >>>> >>>> >>> >> >> >> > -- Kees Cook Chrome OS Security
