[PATCH RFC/RFT 1/3] mm: Introduce ARCH_HAS_USER_SHADOW_STACK

[Deepak Gupta]

From: Mark Brown <broonie@xxxxxxxxxx>

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@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Reviewed-by: Deepak Gupta <debug@xxxxxxxxxxxx>
Reviewed-by: Carlos Bilbao <carlos.bilbao.osdev@xxxxxxxxx>
---
 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 2852fcd82cbd..8ccae77d40f7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1954,6 +1954,7 @@ 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 72f14fd59c2d..23f875e78eae 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -971,7 +971,7 @@ 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
 #if defined(CONFIG_64BIT) || defined(CONFIG_PPC32)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecf63d2b0582..57533b9cae95 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -354,7 +354,7 @@ 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 4c9f5ea13271..4b2a1ef9a161 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1296,6 +1296,12 @@ config NUMA_EMU
 	  into virtual nodes when booted with "numa=fake=N", where N is the
 	  number of nodes. This is only useful for debugging.
 
+config ARCH_HAS_USER_SHADOW_STACK
+	bool
+	help
+	  The architecture has hardware support for userspace shadow call
+          stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
+
 source "mm/damon/Kconfig"
 
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2.45.0