On Tue, Apr 29, 2025 at 11:23:25AM +0100, Lorenzo Stoakes wrote: > On Tue, Apr 29, 2025 at 09:28:05AM +0200, Vlastimil Babka wrote: > > On 4/28/25 17:28, Lorenzo Stoakes wrote: > > > Currently VMA allocation, freeing and duplication exist in kernel/fork.c, > > > which is a violation of separation of concerns, and leaves these functions > > > exposed to the rest of the kernel when they are in fact internal > > > implementation details. > > > > > > Resolve this by moving this logic to mm, and making it internal to vma.c, > > > vma.h. > > > > > > This also allows us, in future, to provide userland testing around this > > > functionality. > > > > > > We additionally abstract dup_mmap() to mm, being careful to ensure > > > kernel/fork.c acceses this via the mm internal header so it is not exposed > > > elsewhere in the kernel. > > > > > > As part of this change, also abstract initial stack allocation performed in > > > __bprm_mm_init() out of fs code into mm via the create_init_stack_vma(), as > > > this code uses vm_area_alloc() and vm_area_free(). > > > > > > In order to do so sensibly, we introduce a new mm/vma_exec.c file, which > > > contains the code that is shared by mm and exec. This file is added to both > > > memory mapping and exec sections in MAINTAINERS so both sets of maintainers > > > can maintain oversight. > > > > Note that kernel/fork.c itself belongs to no section. Maybe we could put it > > somewhere too, maybe also multiple subsystems? I'm thinking something > > between MM, SCHEDULER, EXEC, perhaps PIDFD? > > Thanks, indeed I was wondering about where this should be, and the fact we can > put stuff in multiple places is actually pretty powerful! > > This is on my todo, will take a look at this. Yeah, I'd be interested in having fork.c multi-maintainer-sectioned with EXEC/BINFMT too, when the time comes. -- Kees Cook
