Re: [PATCH RFC RFT v2 1/5] mm: Introduce ARCH_HAS_USER_SHADOW_STACK

[Deepak Gupta <debug@rivosinc.com>]

On Tue, Nov 14, 2023 at 08:05:54PM +0000, Mark Brown wrote:
>Since multiple architectures have support for shadow stacks and we need to
>select support for this feature in several places in the generic code
>provide a generic config option that the architectures can select.
>
>Suggested-by: David Hildenbrand <david@redhat.com>
>Signed-off-by: Mark Brown <broonie@kernel.org>
>---
> arch/x86/Kconfig   | 1 +
> fs/proc/task_mmu.c | 2 +-
> include/linux/mm.h | 2 +-
> mm/Kconfig         | 6 ++++++
> 4 files changed, 9 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>index 3762f41bb092..14b7703a9a2b 100644
>--- a/arch/x86/Kconfig
>+++ b/arch/x86/Kconfig
>@@ -1952,6 +1952,7 @@ config X86_USER_SHADOW_STACK
> 	depends on AS_WRUSS
> 	depends on X86_64
> 	select ARCH_USES_HIGH_VMA_FLAGS
>+	select ARCH_HAS_USER_SHADOW_STACK
> 	select X86_CET
> 	help
> 	  Shadow stack protection is a hardware feature that detects function
>diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>index ef2eb12906da..f0a904aeee8e 100644
>--- a/fs/proc/task_mmu.c
>+++ b/fs/proc/task_mmu.c
>@@ -699,7 +699,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> 		[ilog2(VM_UFFD_MINOR)]	= "ui",
> #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>-#ifdef CONFIG_X86_USER_SHADOW_STACK
>+#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
> 		[ilog2(VM_SHADOW_STACK)] = "ss",
> #endif
> 	};
>diff --git a/include/linux/mm.h b/include/linux/mm.h
>index 418d26608ece..10462f354614 100644
>--- a/include/linux/mm.h
>+++ b/include/linux/mm.h
>@@ -341,7 +341,7 @@ extern unsigned int kobjsize(const void *objp);
> #endif
> #endif /* CONFIG_ARCH_HAS_PKEYS */
>
>-#ifdef CONFIG_X86_USER_SHADOW_STACK
>+#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
> /*
>  * VM_SHADOW_STACK should not be set with VM_SHARED because of lack of
>  * support core mm.
>diff --git a/mm/Kconfig b/mm/Kconfig
>index 89971a894b60..b8638da636e1 100644
>--- a/mm/Kconfig
>+++ b/mm/Kconfig
>@@ -1270,6 +1270,12 @@ config LOCK_MM_AND_FIND_VMA
> 	bool
> 	depends on !STACK_GROWSUP
>
>+config ARCH_HAS_USER_SHADOW_STACK
>+	bool
>+	help
>+	  The architecture has hardware support for userspace shadow call
>+          stacks (eg, x86 CET, arm64 GCS, RISC-V Zisslpcfi).

Minor correction for future version.RISC-V choose to split extension [1, 2].
It's now:

Zicfiss - CFI using shadow stack
Zicfilp - CFI using landing pad

So for shadow stack purposes, we can start saying "RISC-V Zicfiss"

[1] - https://lists.riscv.org/g/tech-ss-lp-cfi/message/55
[2] - https://github.com/riscv/riscv-cfi/pull/126

>+
> source "mm/damon/Kconfig"
>
> endmenu
>
>-- 
>2.30.2
>