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mm/mseal: remove further superfluous comments, do_mseal()

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There's no need to abstract do_mseal() any longer so put the system call
implementation in the system call declaration.

The comment around do_mseal() is strangely formatted, overly long and adds
a lot of superfluous information that the code already provides, so boil
it down to the essentials.

Link: https://lore.kernel.org/20260717-mseal-fixups-v2-3-0daa0014b813@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes (ARM) 2026-07-17 18:27:11 +01:00 committed by Andrew Morton
parent 4c1c2d2418
commit 1b300f679a
1 changed files with 16 additions and 58 deletions
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74
mm/mseal.c
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@ -99,61 +99,25 @@ void mseal_mmap_page_zero(void)
}
/*
* mseal(2) seals the VM's meta data from
* selected syscalls.
* Seal VMAs in the specified input range to prevent an attacker replacing what
* is mapped in the range with something else.
*
* addr/len: VM address range.
* Disallows:
* - VMA unmapping, remapping or shrinking.
* - Overwriting the VMA with another one via mmap(), mremap() or similar.
* - Alteration of properties via mprotect()/pkey_mprotect().
* - Destructive madvise() behaviours (like MADV_DONTNEED) on anonymous read-only
* ranges.
*
* The address range by addr/len must meet:
* start (addr) must be in a valid VMA.
* end (addr + len) must be in a valid VMA.
* no gap (unallocated memory) between start and end.
* start (addr) must be page aligned.
* Since unmapped ranges can be mapped at any time, the input range must span
* mapped ranges only.
*
* len: len will be page aligned implicitly.
*
* Below VMA operations are blocked after sealing.
* 1> Unmapping, moving to another location, and shrinking
* the size, via munmap() and mremap(), can leave an empty
* space, therefore can be replaced with a VMA with a new
* set of attributes.
* 2> Moving or expanding a different vma into the current location,
* via mremap().
* 3> Modifying a VMA via mmap(MAP_FIXED).
* 4> Size expansion, via mremap(), does not appear to pose any
* specific risks to sealed VMAs. It is included anyway because
* the use case is unclear. In any case, users can rely on
* merging to expand a sealed VMA.
* 5> mprotect and pkey_mprotect.
* 6> Some destructive madvice() behavior (e.g. MADV_DONTNEED)
* for anonymous memory, when users don't have write permission to the
* memory. Those behaviors can alter region contents by discarding pages,
* effectively a memset(0) for anonymous memory.
*
* flags: reserved.
*
* return values:
* zero: success.
* -EINVAL:
* invalid input flags.
* start address is not page aligned.
* Address range (start + len) overflow.
* -ENOMEM:
* addr is not a valid address (not allocated).
* end (start + len) is not a valid address.
* a gap (unallocated memory) between start and end.
* -EPERM:
* - In 32 bit architecture, sealing is not supported.
* Note:
* user can call mseal(2) multiple times, adding a seal on an
* already sealed memory is a no-action (no error).
*
* unseal() is not supported.
* The flags parameter is currently reserved.
*/
static int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
SYSCALL_DEFINE3(mseal, unsigned long, start, size_t, len, unsigned long, flags)
{
size_t len_aligned;
unsigned long end;
size_t len;
/* Verify flags not set. */
if (flags)
@ -163,12 +127,12 @@ static int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
if (!PAGE_ALIGNED(start))
return -EINVAL;
len = PAGE_ALIGN(len_in);
len_aligned = PAGE_ALIGN(len);
/* Check to see whether len was rounded up from small -ve to zero. */
if (len_in && !len)
if (len && !len_aligned)
return -EINVAL;
end = start + len;
end = start + len_aligned;
if (end < start)
return -EINVAL;
@ -177,9 +141,3 @@ static int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
return mseal_range(start, end);
}
SYSCALL_DEFINE3(mseal, unsigned long, start, size_t, len, unsigned long,
flags)
{
return do_mseal(start, len, flags);
}