From: Deepak Gupta debug@rivosinc.com
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 https://lore.kernel.org/lkml/20231009-arm64-gcs-v6-12-78e55deaa4dd@kernel.or...
On RISC-V, write-only page table encodings are shadow stack pages. This patch re-defines VM_WRITE only to be VM_SHADOW_STACK.
Next set of patches will set guard rail that no other mm flow can set VM_WRITE only in vma except when specifically creating shadow stack.
Signed-off-by: Deepak Gupta debug@rivosinc.com --- include/linux/mm.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 418d26608ece..dfe0e8118669 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -352,7 +352,19 @@ 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 +/* + * On RISC-V pte encodings for shadow stack is R=0, W=1, X=0 and thus RISCV + * choosing to use similar mechanism on vm_flags where VM_WRITE only means + * VM_SHADOW_STACK. RISCV as well doesn't support VM_SHADOW_STACK to be set + * with VM_SHARED. + */ +#define VM_SHADOW_STACK VM_WRITE +#endif + +#ifndef VM_SHADOW_STACK # define VM_SHADOW_STACK VM_NONE #endif