linux-kernel - [PATCH v3 08/29] mm: Define VM_SHADOW

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Date: Wed,  3 Apr 2024 16:34:56 -0700
From: Deepak Gupta <debug@...osinc.com>
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Subject: [PATCH v3 08/29] mm: Define VM_SHADOW_STACK for RISC-V

VM_SHADOW_STACK is defined by x86 as vm flag to mark a shadow stack vma.

x86 uses VM_HIGH_ARCH_5 bit but that limits shadow stack vma to 64bit only.
arm64 follows same path (see links)

To keep things simple, RISC-V follows the same.
This patch adds `ss` for shadow stack in process maps.

Links:
https://lore.kernel.org/lkml/20231009-arm64-gcs-v6-12-78e55deaa4dd@kernel.org/#r

Signed-off-by: Deepak Gupta <debug@...osinc.com>
---
 fs/proc/task_mmu.c |  3 +++
 include/linux/mm.h | 11 ++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3f78ebbb795f..d9d63eb74f0d 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -702,6 +702,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
 #ifdef CONFIG_X86_USER_SHADOW_STACK
 		[ilog2(VM_SHADOW_STACK)] = "ss",
+#endif
+#ifdef CONFIG_RISCV_USER_CFI
+		[ilog2(VM_SHADOW_STACK)] = "ss",
 #endif
 	};
 	size_t i;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f5a97dec5169..64109f6c70f5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -352,7 +352,16 @@ extern unsigned int kobjsize(const void *objp);
  * for more details on the guard size.
  */
 # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
-#else
+#endif
+
+#ifdef CONFIG_RISCV_USER_CFI
+/*
+ * RISC-V is going along with using VM_HIGH_ARCH_5 bit position for shadow stack
+ */
+#define VM_SHADOW_STACK	VM_HIGH_ARCH_5
+#endif
+
+#ifndef VM_SHADOW_STACK
 # define VM_SHADOW_STACK	VM_NONE
 #endif
 
-- 
2.43.2