new file mode 100644
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <uapi/asm/mman.h>
+
+static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
+ unsigned long pkey __always_unused)
+{
+ unsigned long ret = 0;
+
+ /*
+ * If PROT_WRITE was specified, force it to VM_READ | VM_WRITE.
+ * Only VM_WRITE means shadow stack.
+ */
+ if (prot & PROT_WRITE)
+ ret = (VM_READ | VM_WRITE);
+ return ret;
+}
+#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
+
+#endif /* ! __ASM_MMAN_H__ */
@@ -181,6 +181,7 @@ extern struct pt_alloc_ops pt_ops __meminitdata;
#define PAGE_READ_EXEC __pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC)
#define PAGE_WRITE_EXEC __pgprot(_PAGE_BASE | _PAGE_READ | \
_PAGE_EXEC | _PAGE_WRITE)
+#define PAGE_SHADOWSTACK __pgprot(_PAGE_BASE | _PAGE_WRITE)
#define PAGE_COPY PAGE_READ
#define PAGE_COPY_EXEC PAGE_READ_EXEC
@@ -7,6 +7,7 @@
#include <linux/syscalls.h>
#include <asm/cacheflush.h>
+#include <asm-generic/mman-common.h>
static long riscv_sys_mmap(unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags,
@@ -16,6 +17,15 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
return -EINVAL;
+ /*
+ * If PROT_WRITE is specified then extend that to PROT_READ
+ * protection_map[VM_WRITE] is now going to select shadow stack encodings.
+ * So specifying PROT_WRITE actually should select protection_map [VM_WRITE | VM_READ]
+ * If user wants to create shadow stack then they should use `map_shadow_stack` syscall.
+ */
+ if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
+ prot |= PROT_READ;
+
return ksys_mmap_pgoff(addr, len, prot, flags, fd,
offset >> (PAGE_SHIFT - page_shift_offset));
}
@@ -324,7 +324,7 @@ pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
static const pgprot_t protection_map[16] = {
[VM_NONE] = PAGE_NONE,
[VM_READ] = PAGE_READ,
- [VM_WRITE] = PAGE_COPY,
+ [VM_WRITE] = PAGE_SHADOWSTACK,
[VM_WRITE | VM_READ] = PAGE_COPY,
[VM_EXEC] = PAGE_EXEC,
[VM_EXEC | VM_READ] = PAGE_READ_EXEC,
@@ -47,6 +47,7 @@
#include <linux/oom.h>
#include <linux/sched/mm.h>
#include <linux/ksm.h>
+#include <linux/processor.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
`arch_calc_vm_prot_bits` is implemented on risc-v to return VM_READ | VM_WRITE if PROT_WRITE is specified. Similarly `riscv_sys_mmap` is updated to convert all incoming PROT_WRITE to (PROT_WRITE | PROT_READ). This is to make sure that any existing apps using PROT_WRITE still work. Earlier `protection_map[VM_WRITE]` used to pick read-write PTE encodings. Now `protection_map[VM_WRITE]` will always pick PAGE_SHADOWSTACK PTE encodings for shadow stack. Above changes ensure that existing apps continue to work because underneath kernel will be picking `protection_map[VM_WRITE|VM_READ]` PTE encodings. Signed-off-by: Deepak Gupta <debug@rivosinc.com> --- arch/riscv/include/asm/mman.h | 24 ++++++++++++++++++++++++ arch/riscv/include/asm/pgtable.h | 1 + arch/riscv/kernel/sys_riscv.c | 10 ++++++++++ arch/riscv/mm/init.c | 2 +- mm/mmap.c | 1 + 5 files changed, 37 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/include/asm/mman.h