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mm: introduce vm_mmap_shadow_stack() as a helper for VM_SHADOW_STACK mappings

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Patch series "mm: arch/shstk: Common shadow stack mapping helper and
VM_NOHUGEPAGE", v2.

A series to extract the common shadow stack mmap into a separate helper
for arm64, riscv and x86.


This patch (of 5):

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.

Link: https://lkml.kernel.org/r/20260225161404.3157851-1-catalin.marinas@arm.com
Link: https://lkml.kernel.org/r/20260225161404.3157851-2-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Catalin Marinas 2026-02-25 16:13:58 +00:00 committed by Andrew Morton
parent 03375203e1
commit 2b8acf8450
2 changed files with 27 additions and 0 deletions
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2
include/linux/mm.h
View File

@ -3903,6 +3903,8 @@ 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

25
mm/util.c
View File

@ -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.