| Message ID | 20181217202334.GA11758@jordon-HP-15-Notebook-PC (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
On Tue, Dec 18, 2018 at 01:53:34AM +0530, Souptick Joarder wrote: > Convert to use vm_insert_range() to map range of kernel > memory to user vma. > > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> > Tested-by: Heiko Stuebner <heiko@sntech.de> > Acked-by: Heiko Stuebner <heiko@sntech.de> > --- > drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 19 ++----------------- > 1 file changed, 2 insertions(+), 17 deletions(-) > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > index a8db758..8279084 100644 > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > @@ -221,26 +221,11 @@ static int rockchip_drm_gem_object_mmap_iommu(struct drm_gem_object *obj, > struct vm_area_struct *vma) > { > struct rockchip_gem_object *rk_obj = to_rockchip_obj(obj); > - unsigned int i, count = obj->size >> PAGE_SHIFT; > unsigned long user_count = vma_pages(vma); > - unsigned long uaddr = vma->vm_start; > unsigned long offset = vma->vm_pgoff; > - unsigned long end = user_count + offset; > - int ret; > - > - if (user_count == 0) > - return -ENXIO; > - if (end > count) > - return -ENXIO; > > - for (i = offset; i < end; i++) { > - ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); > - if (ret) > - return ret; > - uaddr += PAGE_SIZE; > - } > - > - return 0; > + return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, > + user_count - offset); This looks like a change in behaviour. If user_count is zero, and offset is zero, then we pass into vm_insert_range() a page_count of zero, and vm_insert_range() does nothing and returns zero. However, as we can see from the above code, the original behaviour was to return -ENXIO in that case. The other thing that I'm wondering is that if (eg) count is 8 (the object is 8 pages), offset is 2, and the user requests mapping 6 pages (user_count = 6), then we call vm_insert_range() with a pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we end up inserting four pages. The original code would calculate end = 6 + 2 = 8. i would iterate from 2 through 8, inserting six pages. (I hadn't spotted that second issue until I'd gone through the calculations manually - which is worrying.) I don't have patches 5 through 9 to look at, but I'm concerned that similar issues also exist in those patches. I'm concerned that this series seems to be introducing subtle bugs, it seems to be unnecessarily difficult to use this function correctly. I think your existing proposal for vm_insert_range() provides an interface that is way too easy to get wrong, and, therefore, is the wrong interface. I think it would be way better to have vm_insert_range() take the object page array without any offset adjustment, and the object page_count again without any adjustment, and have vm_insert_range() itself handle the offsetting and VMA size validation. That would then give a simple interface and probably give a further reduction in code at each call site. Thanks.
On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > On Tue, Dec 18, 2018 at 01:53:34AM +0530, Souptick Joarder wrote: > > Convert to use vm_insert_range() to map range of kernel > > memory to user vma. > > > > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> > > Tested-by: Heiko Stuebner <heiko@sntech.de> > > Acked-by: Heiko Stuebner <heiko@sntech.de> > > --- > > drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 19 ++----------------- > > 1 file changed, 2 insertions(+), 17 deletions(-) > > > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > > index a8db758..8279084 100644 > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c > > @@ -221,26 +221,11 @@ static int rockchip_drm_gem_object_mmap_iommu(struct drm_gem_object *obj, > > struct vm_area_struct *vma) > > { > > struct rockchip_gem_object *rk_obj = to_rockchip_obj(obj); > > - unsigned int i, count = obj->size >> PAGE_SHIFT; > > unsigned long user_count = vma_pages(vma); > > - unsigned long uaddr = vma->vm_start; > > unsigned long offset = vma->vm_pgoff; > > - unsigned long end = user_count + offset; > > - int ret; > > - > > - if (user_count == 0) > > - return -ENXIO; > > - if (end > count) > > - return -ENXIO; > > > > - for (i = offset; i < end; i++) { > > - ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); > > - if (ret) > > - return ret; > > - uaddr += PAGE_SIZE; > > - } > > - > > - return 0; > > + return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, > > + user_count - offset); > > This looks like a change in behaviour. > > If user_count is zero, and offset is zero, then we pass into > vm_insert_range() a page_count of zero, and vm_insert_range() does > nothing and returns zero. > > However, as we can see from the above code, the original behaviour > was to return -ENXIO in that case. I think these checks are not necessary. I am not sure if we get into mmap handlers of driver with user_count = 0. > > The other thing that I'm wondering is that if (eg) count is 8 (the > object is 8 pages), offset is 2, and the user requests mapping 6 > pages (user_count = 6), then we call vm_insert_range() with a > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > end up inserting four pages. Considering the scenario, user_count will remain 8 (user_count = vma_pages(vma) ). ? No ? Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and a pages_count of 8 - 2 = 6. So we end up inserting 6 pages. Please correct me if I am wrong. > > The original code would calculate end = 6 + 2 = 8. i would iterate > from 2 through 8, inserting six pages. > > (I hadn't spotted that second issue until I'd gone through the > calculations manually - which is worrying.) > > I don't have patches 5 through 9 to look at, but I'm concerned that > similar issues also exist in those patches. yes, you were not cc'd for 5 - 9. Below are the patchwork links - https://patchwork.kernel.org/patch/10734269/ https://patchwork.kernel.org/patch/10734271/ https://patchwork.kernel.org/patch/10734273/ https://patchwork.kernel.org/patch/10734277/ https://patchwork.kernel.org/patch/10734279/ > > I'm concerned that this series seems to be introducing subtle bugs, > it seems to be unnecessarily difficult to use this function correctly. > I think your existing proposal for vm_insert_range() provides an > interface that is way too easy to get wrong, and, therefore, is the > wrong interface. > > I think it would be way better to have vm_insert_range() take the > object page array without any offset adjustment, and the object > page_count again without any adjustment, and have vm_insert_range() > itself handle the offsetting and VMA size validation. That would > then give a simple interface and probably give a further reduction > in code at each call site. > > Thanks. > > -- > RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up > According to speedtest.net: 11.9Mbps down 500kbps up
On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > <linux@armlinux.org.uk> wrote: > > This looks like a change in behaviour. > > > > If user_count is zero, and offset is zero, then we pass into > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > nothing and returns zero. > > > > However, as we can see from the above code, the original behaviour > > was to return -ENXIO in that case. > > I think these checks are not necessary. I am not sure if we get into mmap > handlers of driver with user_count = 0. I'm not sure either, I'm just pointing out the change of behaviour. > > The other thing that I'm wondering is that if (eg) count is 8 (the > > object is 8 pages), offset is 2, and the user requests mapping 6 > > pages (user_count = 6), then we call vm_insert_range() with a > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > end up inserting four pages. > > Considering the scenario, user_count will remain 8 (user_count = > vma_pages(vma) ). ? No ? > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > a pages_count > of 8 - 2 = 6. So we end up inserting 6 pages. > > Please correct me if I am wrong. vma_pages(vma) is the number of pages that the user requested, it is the difference between vma->vm_end and vma->vm_start in pages. As I said above, "the user requests mapping 6 pages", so vma_pages() will be 6, and so user_count will also be 6. You are passing user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 in my example. This is two pages short of what the user requested.
On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > <linux@armlinux.org.uk> wrote: > > > This looks like a change in behaviour. > > > > > > If user_count is zero, and offset is zero, then we pass into > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > nothing and returns zero. > > > > > > However, as we can see from the above code, the original behaviour > > > was to return -ENXIO in that case. > > > > I think these checks are not necessary. I am not sure if we get into mmap > > handlers of driver with user_count = 0. > > I'm not sure either, I'm just pointing out the change of behaviour. Ok. I think feedback from Heiko might be helpful here :) > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > pages (user_count = 6), then we call vm_insert_range() with a > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > end up inserting four pages. > > > > Considering the scenario, user_count will remain 8 (user_count = > > vma_pages(vma) ). ? No ? > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > a pages_count > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > Please correct me if I am wrong. > > vma_pages(vma) is the number of pages that the user requested, it is > the difference between vma->vm_end and vma->vm_start in pages. As I > said above, "the user requests mapping 6 pages", so vma_pages() will > be 6, and so user_count will also be 6. You are passing > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > in my example. This is two pages short of what the user requested. > So, this should be the correct behavior. return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, user_count);
On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > <linux@armlinux.org.uk> wrote: > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > <linux@armlinux.org.uk> wrote: > > > > This looks like a change in behaviour. > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > nothing and returns zero. > > > > > > > > However, as we can see from the above code, the original behaviour > > > > was to return -ENXIO in that case. > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > handlers of driver with user_count = 0. > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > end up inserting four pages. > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > vma_pages(vma) ). ? No ? > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > a pages_count > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > Please correct me if I am wrong. > > > > vma_pages(vma) is the number of pages that the user requested, it is > > the difference between vma->vm_end and vma->vm_start in pages. As I > > said above, "the user requests mapping 6 pages", so vma_pages() will > > be 6, and so user_count will also be 6. You are passing > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > in my example. This is two pages short of what the user requested. > > > > So, this should be the correct behavior. > > return vm_insert_range(vma, vma->vm_start, > rk_obj->pages + offset, > user_count); ... and by doing so, you're introducing another instance of the same bug I pointed out in patch 2.
On Tue, Dec 18, 2018 at 6:31 PM Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > > <linux@armlinux.org.uk> wrote: > > > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > > <linux@armlinux.org.uk> wrote: > > > > > This looks like a change in behaviour. > > > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > > nothing and returns zero. > > > > > > > > > > However, as we can see from the above code, the original behaviour > > > > > was to return -ENXIO in that case. > > > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > > handlers of driver with user_count = 0. > > > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > > end up inserting four pages. > > > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > > vma_pages(vma) ). ? No ? > > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > > a pages_count > > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > > > Please correct me if I am wrong. > > > > > > vma_pages(vma) is the number of pages that the user requested, it is > > > the difference between vma->vm_end and vma->vm_start in pages. As I > > > said above, "the user requests mapping 6 pages", so vma_pages() will > > > be 6, and so user_count will also be 6. You are passing > > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > > in my example. This is two pages short of what the user requested. > > > > > > > So, this should be the correct behavior. > > > > return vm_insert_range(vma, vma->vm_start, > > rk_obj->pages + offset, > > user_count); > > ... and by doing so, you're introducing another instance of the same > bug I pointed out in patch 2. Sorry but didn't get it ? How it will be similar to the bug pointed out in patch 2 ? > > -- > RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up > According to speedtest.net: 11.9Mbps down 500kbps up
On Wed, Dec 19, 2018 at 09:01:09AM +0530, Souptick Joarder wrote: > On Tue, Dec 18, 2018 at 6:31 PM Russell King - ARM Linux > <linux@armlinux.org.uk> wrote: > > > > On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > > > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > > > <linux@armlinux.org.uk> wrote: > > > > > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > > > <linux@armlinux.org.uk> wrote: > > > > > > This looks like a change in behaviour. > > > > > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > > > nothing and returns zero. > > > > > > > > > > > > However, as we can see from the above code, the original behaviour > > > > > > was to return -ENXIO in that case. > > > > > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > > > handlers of driver with user_count = 0. > > > > > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > > > > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > > > end up inserting four pages. > > > > > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > > > vma_pages(vma) ). ? No ? > > > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > > > a pages_count > > > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > > > > > Please correct me if I am wrong. > > > > > > > > vma_pages(vma) is the number of pages that the user requested, it is > > > > the difference between vma->vm_end and vma->vm_start in pages. As I > > > > said above, "the user requests mapping 6 pages", so vma_pages() will > > > > be 6, and so user_count will also be 6. You are passing > > > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > > > in my example. This is two pages short of what the user requested. > > > > > > > > > > So, this should be the correct behavior. > > > > > > return vm_insert_range(vma, vma->vm_start, > > > rk_obj->pages + offset, > > > user_count); > > > > ... and by doing so, you're introducing another instance of the same > > bug I pointed out in patch 2. > > Sorry but didn't get it ? How it will be similar to the bug pointed > out in patch 2 ? Towards the top of this function, you have: unsigned long user_count = vma_pages(vma); So what you are proposing does: return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, vma_pages(vma)); Now if we look inside vm_insert_range(): +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr, + struct page **pages, unsigned long page_count) +{ + unsigned long uaddr = addr; + int ret = 0, i; + + if (page_count > vma_pages(vma)) + return -ENXIO; + + for (i = 0; i < page_count; i++) { + ret = vm_insert_page(vma, uaddr, pages[i]); + if (ret < 0) + return ret; + uaddr += PAGE_SIZE; + } So, page_count _is_ vma_pages(vma). So this code does these operations: if (vma_pages(vma) > vma_pages(vma)) return -ENXIO; This will always be false. I've already stated in my reply to patch 2 in paragraph 3 about the uselessness of this test. for (i = 0; i < vma_pages(vma); i++) { ret = vm_insert_page(vma, uaddr, pages[i]); So the loop will iterate over the number of pages that the user requested. Now, taking another example. The object is again 8 pages long, so indexes 0 through 7 in its page array are valid. The user requests 8 pages at offset 2 into the object. Also as already stated in paragraph 3 of my reply to patch 2. vma_pages(vma) is 8. offset = 2. So we end up _inside_ vm_insert_range() with: if (8 > 8) return -ENXIO; As stated, always false. for (i = 0; i < 8; i++) { ret = vm_insert_page(vma, vaddr, rk_obj->pages[2 + i]); Which means we iterate over rk_obj->pages indicies from 2 through 9 inclusive. Since only 0 through 7 are valid, we have walked off the end of the array, and attempted to map an invalid struct page pointer - we could be lucky, and it could point at some struct page (potentially causing us to map some sensitive page - maybe containing your bank details or root password... Or it could oops the kernel.
On Wed, Dec 19, 2018 at 3:02 PM Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > On Wed, Dec 19, 2018 at 09:01:09AM +0530, Souptick Joarder wrote: > > On Tue, Dec 18, 2018 at 6:31 PM Russell King - ARM Linux > > <linux@armlinux.org.uk> wrote: > > > > > > On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > > > > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > This looks like a change in behaviour. > > > > > > > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > > > > nothing and returns zero. > > > > > > > > > > > > > > However, as we can see from the above code, the original behaviour > > > > > > > was to return -ENXIO in that case. > > > > > > > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > > > > handlers of driver with user_count = 0. > > > > > > > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > > > > > > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > > > > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > > > > end up inserting four pages. > > > > > > > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > > > > vma_pages(vma) ). ? No ? > > > > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > > > > a pages_count > > > > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > > > > > > > Please correct me if I am wrong. > > > > > > > > > > vma_pages(vma) is the number of pages that the user requested, it is > > > > > the difference between vma->vm_end and vma->vm_start in pages. As I > > > > > said above, "the user requests mapping 6 pages", so vma_pages() will > > > > > be 6, and so user_count will also be 6. You are passing > > > > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > > > > in my example. This is two pages short of what the user requested. > > > > > > > > > > > > > So, this should be the correct behavior. > > > > > > > > return vm_insert_range(vma, vma->vm_start, > > > > rk_obj->pages + offset, > > > > user_count); > > > > > > ... and by doing so, you're introducing another instance of the same > > > bug I pointed out in patch 2. > > > > Sorry but didn't get it ? How it will be similar to the bug pointed > > out in patch 2 ? > Thanks for the detail explanation. > Towards the top of this function, you have: > > unsigned long user_count = vma_pages(vma); > > So what you are proposing does: > > return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, > vma_pages(vma)); > > Now if we look inside vm_insert_range(): > > +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr, > + struct page **pages, unsigned long page_count) > +{ > + unsigned long uaddr = addr; > + int ret = 0, i; > + > + if (page_count > vma_pages(vma)) > + return -ENXIO; > + > + for (i = 0; i < page_count; i++) { > + ret = vm_insert_page(vma, uaddr, pages[i]); > + if (ret < 0) > + return ret; > + uaddr += PAGE_SIZE; > + } > > So, page_count _is_ vma_pages(vma). So this code does these operations: > > if (vma_pages(vma) > vma_pages(vma)) > return -ENXIO; > > This will always be false. I've already stated in my reply to patch 2 > in paragraph 3 about the uselessness of this test. Agree, this will be always false for this particular/ similar instances. But there are places [3/9], [6/9], [9/9] where page_count is already set and it might be good to just cross check page_count > vma_pages(vma). This was discussed during review of v3 [1/9]. https://patchwork.kernel.org/patch/10716601/ We can discuss again and if not needed it can be removed in v5. > > for (i = 0; i < vma_pages(vma); i++) { > ret = vm_insert_page(vma, uaddr, pages[i]); > > So the loop will iterate over the number of pages that the user requested. > > Now, taking another example. The object is again 8 pages long, so > indexes 0 through 7 in its page array are valid. The user requests > 8 pages at offset 2 into the object. Also as already stated in > paragraph 3 of my reply to patch 2. > > vma_pages(vma) is 8. offset = 2. > > So we end up _inside_ vm_insert_range() with: > > if (8 > 8) > return -ENXIO; > > As stated, always false. > > for (i = 0; i < 8; i++) { > ret = vm_insert_page(vma, vaddr, rk_obj->pages[2 + i]); > > Which means we iterate over rk_obj->pages indicies from 2 through 9 > inclusive. > > Since only 0 through 7 are valid, we have walked off the end of the > array, and attempted to map an invalid struct page pointer - we could > be lucky, and it could point at some struct page (potentially causing > us to map some sensitive page - maybe containing your bank details or > root password... Or it could oops the kernel. Consider the 2nd example. The object is again 8 pages long, so indexes 0 through 7 in its page array are valid. The user requests 8 pages at offset 2 into the object. The original code look like - unsigned long user_count = vma_pages(vma); // 8 unsigned long end = user_count + offset // 8 + 2 = 10 ... for (i = offset (2) ; i < end ( 10) ; i++) { ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); if (ret) return ret; uaddr += PAGE_SIZE; } we iterate over rk_obj->pages indices from 2 through 9. Does it indicates the actual code have a bug when *offset != 0*.
On Wed, Dec 19, 2018 at 05:16:09PM +0530, Souptick Joarder wrote: > On Wed, Dec 19, 2018 at 3:02 PM Russell King - ARM Linux > <linux@armlinux.org.uk> wrote: > > > > On Wed, Dec 19, 2018 at 09:01:09AM +0530, Souptick Joarder wrote: > > > On Tue, Dec 18, 2018 at 6:31 PM Russell King - ARM Linux > > > <linux@armlinux.org.uk> wrote: > > > > > > > > On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > > > > > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > > > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > This looks like a change in behaviour. > > > > > > > > > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > > > > > nothing and returns zero. > > > > > > > > > > > > > > > > However, as we can see from the above code, the original behaviour > > > > > > > > was to return -ENXIO in that case. > > > > > > > > > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > > > > > handlers of driver with user_count = 0. > > > > > > > > > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > > > > > > > > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > > > > > > > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > > > > > end up inserting four pages. > > > > > > > > > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > > > > > vma_pages(vma) ). ? No ? > > > > > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > > > > > a pages_count > > > > > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > > > > > > > > > Please correct me if I am wrong. > > > > > > > > > > > > vma_pages(vma) is the number of pages that the user requested, it is > > > > > > the difference between vma->vm_end and vma->vm_start in pages. As I > > > > > > said above, "the user requests mapping 6 pages", so vma_pages() will > > > > > > be 6, and so user_count will also be 6. You are passing > > > > > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > > > > > in my example. This is two pages short of what the user requested. > > > > > > > > > > > > > > > > So, this should be the correct behavior. > > > > > > > > > > return vm_insert_range(vma, vma->vm_start, > > > > > rk_obj->pages + offset, > > > > > user_count); > > > > > > > > ... and by doing so, you're introducing another instance of the same > > > > bug I pointed out in patch 2. > > > > > > Sorry but didn't get it ? How it will be similar to the bug pointed > > > out in patch 2 ? > > > > Thanks for the detail explanation. > > > Towards the top of this function, you have: > > > > unsigned long user_count = vma_pages(vma); > > > > So what you are proposing does: > > > > return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, > > vma_pages(vma)); > > > > Now if we look inside vm_insert_range(): > > > > +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr, > > + struct page **pages, unsigned long page_count) > > +{ > > + unsigned long uaddr = addr; > > + int ret = 0, i; > > + > > + if (page_count > vma_pages(vma)) > > + return -ENXIO; > > + > > + for (i = 0; i < page_count; i++) { > > + ret = vm_insert_page(vma, uaddr, pages[i]); > > + if (ret < 0) > > + return ret; > > + uaddr += PAGE_SIZE; > > + } > > > > So, page_count _is_ vma_pages(vma). So this code does these operations: > > > > if (vma_pages(vma) > vma_pages(vma)) > > return -ENXIO; > > > > This will always be false. I've already stated in my reply to patch 2 > > in paragraph 3 about the uselessness of this test. > > Agree, this will be always false for this particular/ similar instances. > But there are places [3/9], [6/9], [9/9] where page_count is already set > and it might be good to just cross check page_count > vma_pages(vma). > > This was discussed during review of v3 [1/9]. > https://patchwork.kernel.org/patch/10716601/ > > We can discuss again and if not needed it can be removed in v5. > > > > > for (i = 0; i < vma_pages(vma); i++) { > > ret = vm_insert_page(vma, uaddr, pages[i]); > > > > So the loop will iterate over the number of pages that the user requested. > > > > Now, taking another example. The object is again 8 pages long, so > > indexes 0 through 7 in its page array are valid. The user requests > > 8 pages at offset 2 into the object. Also as already stated in > > paragraph 3 of my reply to patch 2. > > > > vma_pages(vma) is 8. offset = 2. > > > > So we end up _inside_ vm_insert_range() with: > > > > if (8 > 8) > > return -ENXIO; > > > > As stated, always false. > > > > for (i = 0; i < 8; i++) { > > ret = vm_insert_page(vma, vaddr, rk_obj->pages[2 + i]); > > > > Which means we iterate over rk_obj->pages indicies from 2 through 9 > > inclusive. > > > > Since only 0 through 7 are valid, we have walked off the end of the > > array, and attempted to map an invalid struct page pointer - we could > > be lucky, and it could point at some struct page (potentially causing > > us to map some sensitive page - maybe containing your bank details or > > root password... Or it could oops the kernel. > > Consider the 2nd example. > The object is again 8 pages long, so indexes 0 through 7 in > its page array are valid. The user requests 8 pages at offset 2 > into the object. > > The original code look like - > > unsigned long user_count = vma_pages(vma); // 8 > unsigned long end = user_count + offset // 8 + 2 = 10 > ... > for (i = offset (2) ; i < end ( 10) ; i++) { > ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); > if (ret) > return ret; > uaddr += PAGE_SIZE; > } > > we iterate over rk_obj->pages indices from 2 through 9. > Does it indicates the actual code have a bug when *offset != 0*. Please look at _all_ of the original code. Just like in your patch 2, you removed the tests that protect against this overflow: - unsigned int i, count = obj->size >> PAGE_SHIFT; unsigned long user_count = vma_pages(vma); - unsigned long uaddr = vma->vm_start; unsigned long offset = vma->vm_pgoff; - unsigned long end = user_count + offset; - int ret; - - if (user_count == 0) - return -ENXIO; - if (end > count) - return -ENXIO; 'count' will be 8. 'end' will be 10. The existing code would have therefore returned -ENXIO. This is what I'm pointing out in my reviewed of your patches - they remove necessary tests and, by doing so, introduce these array overflows.
On Wed, Dec 19, 2018 at 5:36 PM Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > On Wed, Dec 19, 2018 at 05:16:09PM +0530, Souptick Joarder wrote: > > On Wed, Dec 19, 2018 at 3:02 PM Russell King - ARM Linux > > <linux@armlinux.org.uk> wrote: > > > > > > On Wed, Dec 19, 2018 at 09:01:09AM +0530, Souptick Joarder wrote: > > > > On Tue, Dec 18, 2018 at 6:31 PM Russell King - ARM Linux > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > On Tue, Dec 18, 2018 at 06:24:29PM +0530, Souptick Joarder wrote: > > > > > > On Tue, Dec 18, 2018 at 6:03 PM Russell King - ARM Linux > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > > > On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > > > > > > > > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > > > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > This looks like a change in behaviour. > > > > > > > > > > > > > > > > > > If user_count is zero, and offset is zero, then we pass into > > > > > > > > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > > > > > > > > nothing and returns zero. > > > > > > > > > > > > > > > > > > However, as we can see from the above code, the original behaviour > > > > > > > > > was to return -ENXIO in that case. > > > > > > > > > > > > > > > > I think these checks are not necessary. I am not sure if we get into mmap > > > > > > > > handlers of driver with user_count = 0. > > > > > > > > > > > > > > I'm not sure either, I'm just pointing out the change of behaviour. > > > > > > > > > > > > Ok. I think feedback from Heiko might be helpful here :) > > > > > > > > > > > > > > > > > > > > > > The other thing that I'm wondering is that if (eg) count is 8 (the > > > > > > > > > object is 8 pages), offset is 2, and the user requests mapping 6 > > > > > > > > > pages (user_count = 6), then we call vm_insert_range() with a > > > > > > > > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > > > > > > > > end up inserting four pages. > > > > > > > > > > > > > > > > Considering the scenario, user_count will remain 8 (user_count = > > > > > > > > vma_pages(vma) ). ? No ? > > > > > > > > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > > > > > > > > a pages_count > > > > > > > > of 8 - 2 = 6. So we end up inserting 6 pages. > > > > > > > > > > > > > > > > Please correct me if I am wrong. > > > > > > > > > > > > > > vma_pages(vma) is the number of pages that the user requested, it is > > > > > > > the difference between vma->vm_end and vma->vm_start in pages. As I > > > > > > > said above, "the user requests mapping 6 pages", so vma_pages() will > > > > > > > be 6, and so user_count will also be 6. You are passing > > > > > > > user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 > > > > > > > in my example. This is two pages short of what the user requested. > > > > > > > > > > > > > > > > > > > So, this should be the correct behavior. > > > > > > > > > > > > return vm_insert_range(vma, vma->vm_start, > > > > > > rk_obj->pages + offset, > > > > > > user_count); > > > > > > > > > > ... and by doing so, you're introducing another instance of the same > > > > > bug I pointed out in patch 2. > > > > > > > > Sorry but didn't get it ? How it will be similar to the bug pointed > > > > out in patch 2 ? > > > > > > > Thanks for the detail explanation. > > > > > Towards the top of this function, you have: > > > > > > unsigned long user_count = vma_pages(vma); > > > > > > So what you are proposing does: > > > > > > return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, > > > vma_pages(vma)); > > > > > > Now if we look inside vm_insert_range(): > > > > > > +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr, > > > + struct page **pages, unsigned long page_count) > > > +{ > > > + unsigned long uaddr = addr; > > > + int ret = 0, i; > > > + > > > + if (page_count > vma_pages(vma)) > > > + return -ENXIO; > > > + > > > + for (i = 0; i < page_count; i++) { > > > + ret = vm_insert_page(vma, uaddr, pages[i]); > > > + if (ret < 0) > > > + return ret; > > > + uaddr += PAGE_SIZE; > > > + } > > > > > > So, page_count _is_ vma_pages(vma). So this code does these operations: > > > > > > if (vma_pages(vma) > vma_pages(vma)) > > > return -ENXIO; > > > > > > This will always be false. I've already stated in my reply to patch 2 > > > in paragraph 3 about the uselessness of this test. > > > > Agree, this will be always false for this particular/ similar instances. > > But there are places [3/9], [6/9], [9/9] where page_count is already set > > and it might be good to just cross check page_count > vma_pages(vma). > > > > This was discussed during review of v3 [1/9]. > > https://patchwork.kernel.org/patch/10716601/ > > > > We can discuss again and if not needed it can be removed in v5. > > > > > > > > for (i = 0; i < vma_pages(vma); i++) { > > > ret = vm_insert_page(vma, uaddr, pages[i]); > > > > > > So the loop will iterate over the number of pages that the user requested. > > > > > > Now, taking another example. The object is again 8 pages long, so > > > indexes 0 through 7 in its page array are valid. The user requests > > > 8 pages at offset 2 into the object. Also as already stated in > > > paragraph 3 of my reply to patch 2. > > > > > > vma_pages(vma) is 8. offset = 2. > > > > > > So we end up _inside_ vm_insert_range() with: > > > > > > if (8 > 8) > > > return -ENXIO; > > > > > > As stated, always false. > > > > > > for (i = 0; i < 8; i++) { > > > ret = vm_insert_page(vma, vaddr, rk_obj->pages[2 + i]); > > > > > > Which means we iterate over rk_obj->pages indicies from 2 through 9 > > > inclusive. > > > > > > Since only 0 through 7 are valid, we have walked off the end of the > > > array, and attempted to map an invalid struct page pointer - we could > > > be lucky, and it could point at some struct page (potentially causing > > > us to map some sensitive page - maybe containing your bank details or > > > root password... Or it could oops the kernel. > > > > Consider the 2nd example. > > The object is again 8 pages long, so indexes 0 through 7 in > > its page array are valid. The user requests 8 pages at offset 2 > > into the object. > > > > The original code look like - > > > > unsigned long user_count = vma_pages(vma); // 8 > > unsigned long end = user_count + offset // 8 + 2 = 10 > > ... > > for (i = offset (2) ; i < end ( 10) ; i++) { > > ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); > > if (ret) > > return ret; > > uaddr += PAGE_SIZE; > > } > > > > we iterate over rk_obj->pages indices from 2 through 9. > > Does it indicates the actual code have a bug when *offset != 0*. > > Please look at _all_ of the original code. > > Just like in your patch 2, you removed the tests that protect against > this overflow: > > - unsigned int i, count = obj->size >> PAGE_SHIFT; > unsigned long user_count = vma_pages(vma); > - unsigned long uaddr = vma->vm_start; > unsigned long offset = vma->vm_pgoff; > - unsigned long end = user_count + offset; > - int ret; > - > - if (user_count == 0) > - return -ENXIO; > - if (end > count) > - return -ENXIO; > > 'count' will be 8. 'end' will be 10. The existing code would have > therefore returned -ENXIO. > > This is what I'm pointing out in my reviewed of your patches - they > remove necessary tests and, by doing so, introduce these array > overflows. I change the code accordingly. Does it looks good ? @@ -221,26 +221,18 @@ static int rockchip_drm_gem_object_mmap_iommu(struct drm_gem_object *obj, struct vm_area_struct *vma) { struct rockchip_gem_object *rk_obj = to_rockchip_obj(obj); - unsigned int i, count = obj->size >> PAGE_SHIFT; + unsigned int count = obj->size >> PAGE_SHIFT; unsigned long user_count = vma_pages(vma); - unsigned long uaddr = vma->vm_start; unsigned long offset = vma->vm_pgoff; unsigned long end = user_count + offset; - int ret; if (user_count == 0) return -ENXIO; if (end > count) return -ENXIO; - for (i = offset; i < end; i++) { - ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); - if (ret) - return ret; - uaddr += PAGE_SIZE; - } - - return 0; + return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, + user_count);
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c index a8db758..8279084 100644 --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c @@ -221,26 +221,11 @@ static int rockchip_drm_gem_object_mmap_iommu(struct drm_gem_object *obj, struct vm_area_struct *vma) { struct rockchip_gem_object *rk_obj = to_rockchip_obj(obj); - unsigned int i, count = obj->size >> PAGE_SHIFT; unsigned long user_count = vma_pages(vma); - unsigned long uaddr = vma->vm_start; unsigned long offset = vma->vm_pgoff; - unsigned long end = user_count + offset; - int ret; - - if (user_count == 0) - return -ENXIO; - if (end > count) - return -ENXIO; - for (i = offset; i < end; i++) { - ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]); - if (ret) - return ret; - uaddr += PAGE_SIZE; - } - - return 0; + return vm_insert_range(vma, vma->vm_start, rk_obj->pages + offset, + user_count - offset); } static int rockchip_drm_gem_object_mmap_dma(struct drm_gem_object *obj,