svn commit: r340231 - head/sys/kern

[John Baldwin]

On 11/7/18 3:08 PM, Konstantin Belousov wrote:
> On Wed, Nov 07, 2018 at 01:35:57PM -0800, John Baldwin wrote:
>> On 11/7/18 1:01 PM, Ed Schouten wrote:
>>> Op wo 7 nov. 2018 om 19:32 schreef John Baldwin <jhb at freebsd.org>:
>>>> Modified: head/sys/kern/imgact_elf.c
>>>> ==============================================================================
>>>> --- head/sys/kern/imgact_elf.c  Wed Nov  7 18:29:54 2018        (r340230)
>>>> +++ head/sys/kern/imgact_elf.c  Wed Nov  7 18:32:02 2018        (r340231)
>>>> @@ -120,7 +120,8 @@ SYSCTL_INT(_debug, OID_AUTO, __elfN(legacy_coredump),
>>>>
>>>>  int __elfN(nxstack) =
>>>>  #if defined(__amd64__) || defined(__powerpc64__) /* both 64 and 32 bit */ || \
>>>> -    (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
>>>> +    (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__) || \
>>>> +    defined(__riscv)
>>>>         1;
>>>>  #else
>>>>         0;
>>>
>>> Are we getting to the point that it might make sense to invert this
>>> logic, i.e., just list the architectures that require executable
>>> stacks?
>>
>> It's not clear.  The remaining set is i386 (should be able to use nxstack
>> when using PAE and PG_NX is supported), MIPS (no X permission in PTEs),
>> 32-bit powerpc (no X permissions in PTEs AFAICT), and sparc64 (no X
>> permissions in PTEs AFAICT).  For architectures without X ptes, removing
>> VM_PROT_EXECUTE from the stack permissions is a no-op and would be
>> harmless, so we could perhaps just default this to always on at this
>> point?
> AFAIR sparc64 ABI defines its stack as nx always (and PTEs do allow to
> control exec permission).

Hmm, I couldn't find any uses of VM_PROT_EXECUTE in pmap.c that seemed to
affect permissions.  There is a software TTE bit that is used to know which
address ranges require icache flushing, but it seems to only be used for
that.

Regardless, for the purposes of this sysctl, is there any reason we can't
just define it to 1 always now?  It is only honored if the architecture
is using a shared page to hold the signal trampoline and only has an effect
if the pmap honors VM_PROT_EXECUTE.  That would at least fix i386 with
PAE to DTRT I think.

-- 
John Baldwin