[PATCH v3 1/1] drm/ttm: Fix COW check
Daniel Vetter
daniel at ffwll.ch
Wed Jul 14 11:15:01 UTC 2021
On Wed, Jul 14, 2021 at 12:51:15PM +0200, Christian König wrote:
> Am 14.07.21 um 12:44 schrieb Daniel Vetter:
> > On Mon, Jul 12, 2021 at 06:06:36PM -0400, Felix Kuehling wrote:
> > > KFD Thunk maps invisible VRAM BOs with PROT_NONE, MAP_PRIVATE.
> > > is_cow_mapping returns true for these mappings. Add a check for
> > > vm_flags & VM_WRITE to avoid mmap failures on private read-only or
> > > PROT_NONE mappings.
> > >
> > > v2: protect against mprotect making a mapping writable after the fact
> > > v3: update driver-specific vm_operations_structs
> > >
> > > Fixes: f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3")
> > > Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
> > > Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> > So looking at vmf_insert_pfn_prot() and the comment there we can't have
> > VM_PFNMAP and is_cow_mapping ever be true, or things break. On platforms
> > without pte_special at least.
>
> Key idea is that we never end up in vmf_insert_pfn_prot() because the vma is
> mapped with PROT_NONE.
Ah right if it's PROT_NONE then it's ok. But the code here only checks for
VM_WRITE, not VM_READ, so PROT_READ can get through and go boom? Or
something else I'm missing?
Maybe time for a few amdgpu mmap tests that go through the combos and make
sure it works/fails all correctly.
-Daniel
> > So I'm not sure this is a great idea, and definitely not for all drivers
>
> Yeah, I'm absolutely not happy with this either but it seemed to be the
> least painful thing to do.
>
> > ...
> >
> > Can we clear VM_MAYWRITE instead to force this to be a non-cow mapping
> > instead?
>
> Well we have considered forcefully setting VM_SHARED, which won't work
> easily for a couple of reasons.
>
> But clearing VM_MAYWRITE in amdgpu/amdkfd may actually work as well.
>
> Felix can you test this?
>
> Thanks,
> Christian.
>
> > -Daniel
> >
> > > ---
> > > drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 3 ++-
> > > drivers/gpu/drm/nouveau/nouveau_gem.c | 3 ++-
> > > drivers/gpu/drm/radeon/radeon_gem.c | 3 ++-
> > > drivers/gpu/drm/ttm/ttm_bo_vm.c | 14 +++++++++++++-
> > > drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c | 1 +
> > > include/drm/ttm/ttm_bo_api.h | 4 ++++
> > > 6 files changed, 24 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > > index b3404c43a911..1aa750a6a5d2 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > > @@ -79,7 +79,8 @@ static const struct vm_operations_struct amdgpu_gem_vm_ops = {
> > > .fault = amdgpu_gem_fault,
> > > .open = ttm_bo_vm_open,
> > > .close = ttm_bo_vm_close,
> > > - .access = ttm_bo_vm_access
> > > + .access = ttm_bo_vm_access,
> > > + .mprotect = ttm_bo_vm_mprotect
> > > };
> > > static void amdgpu_gem_object_free(struct drm_gem_object *gobj)
> > > diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > > index 5b27845075a1..164ea564bb7a 100644
> > > --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > > +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > > @@ -70,7 +70,8 @@ static const struct vm_operations_struct nouveau_ttm_vm_ops = {
> > > .fault = nouveau_ttm_fault,
> > > .open = ttm_bo_vm_open,
> > > .close = ttm_bo_vm_close,
> > > - .access = ttm_bo_vm_access
> > > + .access = ttm_bo_vm_access,
> > > + .mprotect = ttm_bo_vm_mprotect
> > > };
> > > void
> > > diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
> > > index 458f92a70887..c19ad07eb7b5 100644
> > > --- a/drivers/gpu/drm/radeon/radeon_gem.c
> > > +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> > > @@ -77,7 +77,8 @@ static const struct vm_operations_struct radeon_gem_vm_ops = {
> > > .fault = radeon_gem_fault,
> > > .open = ttm_bo_vm_open,
> > > .close = ttm_bo_vm_close,
> > > - .access = ttm_bo_vm_access
> > > + .access = ttm_bo_vm_access,
> > > + .mprotect = ttm_bo_vm_mprotect
> > > };
> > > static void radeon_gem_object_free(struct drm_gem_object *gobj)
> > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > index f56be5bc0861..fb325bad5db6 100644
> > > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > @@ -542,17 +542,29 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
> > > }
> > > EXPORT_SYMBOL(ttm_bo_vm_access);
> > > +int ttm_bo_vm_mprotect(struct vm_area_struct *vma, unsigned long start,
> > > + unsigned long end, unsigned long newflags)
> > > +{
> > > + /* Enforce no COW since would have really strange behavior with it. */
> > > + if (is_cow_mapping(newflags) && (newflags & VM_WRITE))
> > > + return -EINVAL;
> > > +
> > > + return 0;
> > > +}
> > > +EXPORT_SYMBOL(ttm_bo_vm_mprotect);
> > > +
> > > static const struct vm_operations_struct ttm_bo_vm_ops = {
> > > .fault = ttm_bo_vm_fault,
> > > .open = ttm_bo_vm_open,
> > > .close = ttm_bo_vm_close,
> > > .access = ttm_bo_vm_access,
> > > + .mprotect = ttm_bo_vm_mprotect,
> > > };
> > > int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
> > > {
> > > /* Enforce no COW since would have really strange behavior with it. */
> > > - if (is_cow_mapping(vma->vm_flags))
> > > + if (is_cow_mapping(vma->vm_flags) && (vma->vm_flags & VM_WRITE))
> > > return -EINVAL;
> > > ttm_bo_get(bo);
> > > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > > index e6b1f98ec99f..e4bf7dc99320 100644
> > > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > > @@ -61,6 +61,7 @@ int vmw_mmap(struct file *filp, struct vm_area_struct *vma)
> > > .fault = vmw_bo_vm_fault,
> > > .open = ttm_bo_vm_open,
> > > .close = ttm_bo_vm_close,
> > > + .mprotect = ttm_bo_vm_mprotect,
> > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > > .huge_fault = vmw_bo_vm_huge_fault,
> > > #endif
> > > diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> > > index f681bbdbc698..40eb95875355 100644
> > > --- a/include/drm/ttm/ttm_bo_api.h
> > > +++ b/include/drm/ttm/ttm_bo_api.h
> > > @@ -605,6 +605,10 @@ void ttm_bo_vm_close(struct vm_area_struct *vma);
> > > int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
> > > void *buf, int len, int write);
> > > +
> > > +int ttm_bo_vm_mprotect(struct vm_area_struct *vma, unsigned long start,
> > > + unsigned long end, unsigned long newflags);
> > > +
> > > bool ttm_bo_delayed_delete(struct ttm_device *bdev, bool remove_all);
> > > vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
> > > --
> > > 2.32.0
> > >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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