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

[Jan Beulich <jbeulich@xxxxxxxx>]

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?

Jan