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mseal: replace can_modify_mm_madv with a vma variant

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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: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Lorenzo 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Pedro Falcato 2024-08-17 01:18:32 +01:00 committed by Andrew Morton
parent 38075679b5
commit 23c57d1fa2
4 changed files with 14 additions and 25 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
mm/internal.h
View file

@ -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)
{

13
mm/madvise.c
View file

@ -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

15
mm/mseal.c
View file

@ -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. */

7
mm/vma.h
View file

@ -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 */