[PATCH v2 1/5] mm: Introduce vm_mmap_shadow_stack() as a helper for VM_SHADOW_STACK mappings
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2026-02-25 16:14:14
Also in:
linux-mm, linux-riscv, lkml
Subsystem:
memory management, memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
arm64, riscv and x86 use a similar pattern for mapping the user shadow stack (cloned from x86). Extract this into a helper to facilitate code reuse. The call to do_mmap() from the new helper uses PROT_READ|PROT_WRITE prot bits instead of the PROT_READ with an explicit VM_WRITE vm_flag. The x86 intent was to avoid PROT_WRITE implying normal write since the shadow stack is not writable by normal stores. However, from a kernel perspective, the vma is writeable. Functionally there is no difference. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Tested-by: Deepak Gupta <redacted> Reviewed-by: Mark Brown <broonie@kernel.org> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> --- include/linux/mm.h | 2 ++ mm/util.c | 25 +++++++++++++++++++++++++ 2 files changed, 27 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5be3d8a8f806..61071dd72eb6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -3908,6 +3908,8 @@ extern int vm_munmap(unsigned long, size_t); extern unsigned long __must_check vm_mmap(struct file *, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long); +extern unsigned long __must_check vm_mmap_shadow_stack(unsigned long addr, + unsigned long len, unsigned long flags); struct vm_unmapped_area_info { #define VM_UNMAPPED_AREA_TOPDOWN 1
diff --git a/mm/util.c b/mm/util.c
index b05ab6f97e11..51f7f417e91f 100644
--- a/mm/util.c
+++ b/mm/util.c@@ -618,6 +618,31 @@ unsigned long vm_mmap(struct file *file, unsigned long addr, } EXPORT_SYMBOL(vm_mmap); +#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK +/* + * Perform a userland memory mapping for a shadow stack into the current + * process address space. This is intended to be used by architectures that + * support user shadow stacks. + */ +unsigned long vm_mmap_shadow_stack(unsigned long addr, unsigned long len, + unsigned long flags) +{ + struct mm_struct *mm = current->mm; + unsigned long ret, unused; + + flags |= MAP_ANONYMOUS | MAP_PRIVATE; + if (addr) + flags |= MAP_FIXED_NOREPLACE; + + mmap_write_lock(mm); + ret = do_mmap(NULL, addr, len, PROT_READ | PROT_WRITE, flags, + VM_SHADOW_STACK, 0, &unused, NULL); + mmap_write_unlock(mm); + + return ret; +} +#endif /* CONFIG_ARCH_HAS_USER_SHADOW_STACK */ + /** * __vmalloc_array - allocate memory for a virtually contiguous array. * @n: number of elements.