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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/01/2025 1:47 pm, Jan Beulich wrote:
> 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

Thankyou.

~Andrew