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@google.com Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails") Cc: stable stable@kernel.org Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Jann Horn jannh@google.com Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com --- 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 db4741007bef..651705c2bf47 100644 --- a/include/linux/mman.h +++ b/include/linux/mman.h @@ -187,16 +187,31 @@ static inline bool arch_memory_deny_write_exec_supported(void) * * d) mmap(PROT_READ | PROT_EXEC) * mmap(PROT_READ | PROT_EXEC | PROT_BTI) + * + * 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) { + /* 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 do not accept newly writably executable VMAs... */ + if (new & VM_WRITE) return true;
- if (!(vma->vm_flags & VM_EXEC) && (vm_flags & VM_EXEC)) + /* ...nor previously non-executable VMAs becoming executable. */ + if (!(old & VM_EXEC)) return true;
return false; diff --git a/mm/mmap.c b/mm/mmap.c index 9fefd13640d1..d71ac65563b2 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2826,7 +2826,7 @@ 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 b94fbb45d5c7..7e870a8c9402 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -791,7 +791,7 @@ 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; }