* Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> [241022 16:41]:
> Refactor the map_deny_write_exec() to not unnecessarily require a VMA
> parameter but rather to accept VMA flags parameters, which allows us to use
> this function early in mmap_region() in a subsequent commit.
>
> While we're here, we refactor the function to be more readable and add some
> additional documentation.
>
> Reported-by: Jann Horn <jannh@xxxxxxxxxx>
> Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
> Cc: stable <stable@xxxxxxxxxx>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> include/linux/mman.h | 21 ++++++++++++++++++---
> mm/mmap.c | 2 +-
> mm/mprotect.c | 2 +-
> 3 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mman.h b/include/linux/mman.h
> index bcb201ab7a41..d71f83b821ef 100644
> --- a/include/linux/mman.h
> +++ b/include/linux/mman.h
> @@ -188,16 +188,31 @@ static inline bool arch_memory_deny_write_exec_supported(void)
> *
> * d) mmap(PROT_READ | PROT_EXEC)
> * mmap(PROT_READ | PROT_EXEC | PROT_BTI)
nit: the arguments are not in the comments (which is a pre-existing
issue).
> + *
> + * This is only applicable if the user has set the Memory-Deny-Write-Execute
> + * (MDWE) protection mask for the current process.
> + *
> + * @old specifies the VMA flags the VMA originally possessed, and @new the ones
> + * we propose to set.
> + *
> + * Return: false if proposed change is OK, true if not ok and should be denied.
> */
> -static inline bool map_deny_write_exec(struct vm_area_struct *vma, unsigned long vm_flags)
> +static inline bool map_deny_write_exec(unsigned long old, unsigned long new)
Nit: somehow "new" is special in my editor. Also, I'm too lazy to fix
my editor so I'll live with it.
> {
> + /* If MDWE is disabled, we have nothing to deny. */
> if (!test_bit(MMF_HAS_MDWE, ¤t->mm->flags))
> return false;
>
> - if ((vm_flags & VM_EXEC) && (vm_flags & VM_WRITE))
> + /* If the new VMA is not executable, we have nothing to deny. */
> + if (!(new & VM_EXEC))
> + return false;
> +
> + /* Under MDWE we absolutely do not accept writably executable... */
> + if (new & VM_WRITE)
> return true;
>
> - if (!(vma->vm_flags & VM_EXEC) && (vm_flags & VM_EXEC))
> + /* ...nor newly executable VMAs. */
> + if (!(old & VM_EXEC))
> return true;
>
> return false;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index d55c58e99a54..66edf0ebba94 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1508,7 +1508,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> vma_set_anonymous(vma);
> }
>
> - if (map_deny_write_exec(vma, vma->vm_flags)) {
> + if (map_deny_write_exec(vma->vm_flags, vma->vm_flags)) {
> error = -EACCES;
> goto close_and_free_vma;
> }
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 0c5d6d06107d..6f450af3252e 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -810,7 +810,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
> break;
> }
>
> - if (map_deny_write_exec(vma, newflags)) {
> + if (map_deny_write_exec(vma->vm_flags, newflags)) {
> error = -EACCES;
> break;
> }
> --
> 2.47.0
