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| author | Lorenzo Stoakes <lorenzo.stoakes@oracle.com> | 2024-12-03 19:05:10 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-01-14 07:40:43 +0100 |
| commit | 7a5714991872f0a4805cc6004a5bff19a71d0459 (patch) | |
| tree | a745ab0a6f9257c6e63f805c71a7d6d8aef2d2dc /fs | |
| parent | mm/vma: move unmapped_area() internals to mm/vma.c (diff) | |
| download | linux-7a5714991872f0a4805cc6004a5bff19a71d0459.tar.xz linux-7a5714991872f0a4805cc6004a5bff19a71d0459.zip | |
mm: abstract get_arg_page() stack expansion and mmap read lock
Right now fs/exec.c invokes expand_downwards(), an otherwise internal
implementation detail of the VMA logic in order to ensure that an arg page
can be obtained by get_user_pages_remote().
In order to be able to move the stack expansion logic into mm/vma.c to
make it available to userland testing we need to find an alternative
approach here.
We do so by providing the mmap_read_lock_maybe_expand() function which
also helpfully documents what get_arg_page() is doing here and adds an
additional check against VM_GROWSDOWN to make explicit that the stack
expansion logic is only invoked when the VMA is indeed a downward-growing
stack.
This allows expand_downwards() to become a static function.
Importantly, the VMA referenced by mmap_read_maybe_expand() must NOT be
currently user-visible in any way, that is place within an rmap or VMA
tree. It must be a newly allocated VMA.
This is the case when exec invokes this function.
Link: https://lkml.kernel.org/r/5295d1c70c58e6aa63d14be68d4e1de9fa1c8e6d.1733248985.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/exec.c | 14 |
1 files changed, 3 insertions, 11 deletions
diff --git a/fs/exec.c b/fs/exec.c index 98cb7ba9983c..1e1f79c514de 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -205,18 +205,10 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, /* * Avoid relying on expanding the stack down in GUP (which * does not work for STACK_GROWSUP anyway), and just do it - * by hand ahead of time. + * ahead of time. */ - if (write && pos < vma->vm_start) { - mmap_write_lock(mm); - ret = expand_downwards(vma, pos); - if (unlikely(ret < 0)) { - mmap_write_unlock(mm); - return NULL; - } - mmap_write_downgrade(mm); - } else - mmap_read_lock(mm); + if (!mmap_read_lock_maybe_expand(mm, vma, pos, write)) + return NULL; /* * We are doing an exec(). 'current' is the process |