Re: [PATCH v3 0/3] Add stack protector

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.01.2025 14:28, Andrew Cooper wrote:
> On 14/01/2025 1:22 pm, Jan Beulich wrote:
>> On 12.12.2024 02:17, Andrew Cooper wrote:
>>> On 12/12/2024 12:13 am, Volodymyr Babchuk wrote:
>>>> Hello Jan,
>>>>
>>>> Jan Beulich <jbeulich@xxxxxxxx> writes:
>>>>
>>>>> On 11.12.2024 03:04, Volodymyr Babchuk wrote:
>>>>>> Both GCC and Clang support -fstack-protector feature, which add stack
>>>>>> canaries to functions where stack corruption is possible. This series
>>>>>> makes possible to use this feature in Xen. I tested this on ARM64 and
>>>>>> it is working as intended. Tested both with GCC and Clang.
>>>>>>
>>>>>> It is hard to enable this feature on x86, as GCC stores stack canary
>>>>>> in %fs:40 by default, but Xen can't use %fs for various reasons. It is
>>>>>> possibly to change stack canary location new newer GCC versions, but
>>>>>> this will change minimal GCC requirement, which is also hard due to
>>>>>> various reasons. So, this series focus mostly on ARM and RISCV.
>>>>> Why exactly would it not be possible to offer the feature when new enough
>>>>> gcc is in use?
>>>> It is possible to use this feature with a modern enough GCC, yes. Are
>>>> you suggesting to make HAS_STACK_PROTECTOR dependent on GCC_VERSION for
>>>> x86 platform?
>>> (With the knowledge that this is a disputed Kconfig pattern, and will
>>> need rebasing), the way I want this to work is simply:
>>>
>>> diff --git a/xen/Makefile b/xen/Makefile
>>> index 0de0101fd0bf..5d0a88fb3c3f 100644
>>> --- a/xen/Makefile
>>> +++ b/xen/Makefile
>>> @@ -434,6 +434,9 @@ endif
>>>  
>>>  ifeq ($(CONFIG_STACK_PROTECTOR),y)
>>>  CFLAGS += -fstack-protector
>>> +ifeq ($(CONFIG_X86),y)
>>> +CFLAGS += -mstack-protector-guard=global
>>> +endif
>>>  else
>>>  CFLAGS += -fno-stack-protector
>>>  endif
>>> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
>>> index 9cdd04721afa..7951ca908b36 100644
>>> --- a/xen/arch/x86/Kconfig
>>> +++ b/xen/arch/x86/Kconfig
>>> @@ -28,6 +28,7 @@ config X86
>>>         select HAS_PCI_MSI
>>>         select HAS_PIRQ
>>>         select HAS_SCHED_GRANULARITY
>>> +       select HAS_STACK_PROTECTOR if
>>> $(cc-option,-mstack-protector-guard=global)
>>>         select HAS_UBSAN
>>>         select HAS_VMAP
>>>         select HAS_VPCI if HVM
>>>
>>>
>>>
>>> Sadly, it doesn't build.  I get a handful of:
>>>
>>> prelink.o: in function `cmdline_parse':
>>> /home/andrew/xen.git/xen/common/kernel.c:216:(.init.text+0x20f2): failed
>>> to convert GOTPCREL relocation against '__stack_chk_guard'; relink with
>>> --no-relax
>>> /home/andrew/xen.git/xen/common/kernel.c:230:(.init.text+0x246f): failed
>>> to convert GOTPCREL relocation against '__stack_chk_guard'; relink with
>>> --no-relax
>>>
>>> which is more toolchain-whispering than I feel like doing tonight.
>> For reference:
>> https://sourceware.org/pipermail/binutils/2025-January/138631.html
>>
>> You didn't enter a gcc bug report yet, did you?
> 
> No, not yet.  I'm afraid I've not had the time.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118473

Jan