Commit 23c57d1f authored by Pedro Falcato's avatar Pedro Falcato Committed by Andrew Morton
Browse files

mseal: replace can_modify_mm_madv with a vma variant 

Replace can_modify_mm_madv() with a single vma variant, and associated
checks in madvise.

While we're at it, also invert the order of checks in:
 if (unlikely(is_ro_anon(vma) && !can_modify_vma(vma))

Checking if we can modify the vma itself (through vm_flags) is certainly
cheaper than is_ro_anon() due to arch_vma_access_permitted() looking at
e.g pkeys registers (with extra branches) in some architectures.

This patch allows for partial madvise success when finding a sealed VMA,
which historically has been allowed in Linux.

Link: https://lkml.kernel.org/r/20240817-mseal-depessimize-v3-5-d8d2e037df30@gmail.com


Signed-off-by: default avatarPedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 38075679

mm/internal.h

+0 −2
Original line number Diff line number Diff line
@@ -1361,8 +1361,6 @@ static inline int can_do_mseal(unsigned long flags) 


bool can_modify_mm(struct mm_struct *mm, unsigned long start,

		unsigned long end);

bool can_modify_mm_madv(struct mm_struct *mm, unsigned long start,

		unsigned long end, int behavior);

#else

static inline int can_do_mseal(unsigned long flags)

{

mm/madvise.c

+3 −10
Original line number Diff line number Diff line
@@ -1031,6 +1031,9 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, 
	struct anon_vma_name *anon_name;

	unsigned long new_flags = vma->vm_flags;



	if (unlikely(!can_modify_vma_madv(vma, behavior)))

		return -EPERM;



	switch (behavior) {

	case MADV_REMOVE:

		return madvise_remove(vma, prev, start, end);
@@ -1448,15 +1451,6 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh 
	start = untagged_addr_remote(mm, start);

	end = start + len;



	/*

	 * Check if the address range is sealed for do_madvise().

	 * can_modify_mm_madv assumes we have acquired the lock on MM.

	 */

	if (unlikely(!can_modify_mm_madv(mm, start, end, behavior))) {

		error = -EPERM;

		goto out;

	}



	blk_start_plug(&plug);

	switch (behavior) {

	case MADV_POPULATE_READ:
@@ -1470,7 +1464,6 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh 
	}

	blk_finish_plug(&plug);



out:

	if (write)

		mmap_write_unlock(mm);

	else

mm/mseal.c

+4 −13
Original line number Diff line number Diff line
@@ -75,23 +75,14 @@ bool can_modify_mm(struct mm_struct *mm, unsigned long start, unsigned long end) 
}



/*

 * Check if the vmas of a memory range are allowed to be modified by madvise.

 * the memory ranger can have a gap (unallocated memory).

 * return true, if it is allowed.

 * Check if a vma is allowed to be modified by madvise.

 */

bool can_modify_mm_madv(struct mm_struct *mm, unsigned long start, unsigned long end,

		int behavior)

bool can_modify_vma_madv(struct vm_area_struct *vma, int behavior)

{

	struct vm_area_struct *vma;



	VMA_ITERATOR(vmi, mm, start);



	if (!is_madv_discard(behavior))

		return true;



	/* going through each vma to check. */

	for_each_vma_range(vmi, vma, end)

		if (unlikely(is_ro_anon(vma) && !can_modify_vma(vma)))

	if (unlikely(!can_modify_vma(vma) && is_ro_anon(vma)))

		return false;



	/* Allow by default. */

mm/vma.h

+7 −0
Original line number Diff line number Diff line
@@ -380,6 +380,8 @@ static inline bool can_modify_vma(struct vm_area_struct *vma) 
	return true;

}



bool can_modify_vma_madv(struct vm_area_struct *vma, int behavior);



#else



static inline bool can_modify_vma(struct vm_area_struct *vma)
@@ -387,6 +389,11 @@ static inline bool can_modify_vma(struct vm_area_struct *vma) 
	return true;

}



static inline bool can_modify_vma_madv(struct vm_area_struct *vma, int behavior)

{

	return true;

}



#endif



#endif	/* __MM_VMA_H */