From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 8 Oct 2020 18:44:40 +0200 From: Gerald Schaefer Subject: Re: [PATCH 08/13] s390/pci: Remove races against pte updates Message-ID: <20201008184440.4c3bebed@thinkpad> In-Reply-To: <20201007164426.1812530-9-daniel.vetter@ffwll.ch> References: <20201007164426.1812530-1-daniel.vetter@ffwll.ch> <20201007164426.1812530-9-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable List-ID: To: Daniel Vetter Cc: DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Daniel Vetter , Jason Gunthorpe , Dan Williams , Kees Cook , Andrew Morton , John Hubbard , =?UTF-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Niklas Schnelle On Wed, 7 Oct 2020 18:44:21 +0200 Daniel Vetter wrote: > Way back it was a reasonable assumptions that iomem mappings never > change the pfn range they point at. But this has changed: >=20 > - gpu drivers dynamically manage their memory nowadays, invalidating > ptes with unmap_mapping_range when buffers get moved >=20 > - contiguous dma allocations have moved from dedicated carvetouts to > cma regions. This means if we miss the unmap the pfn might contain > pagecache or anon memory (well anything allocated with GFP_MOVEABLE) >=20 > - even /dev/mem now invalidates mappings when the kernel requests that > iomem region when CONFIG_IO_STRICT_DEVMEM is set, see 3234ac664a87 > ("/dev/mem: Revoke mappings when a driver claims the region") >=20 > Accessing pfns obtained from ptes without holding all the locks is > therefore no longer a good idea. Fix this. >=20 > Since zpci_memcpy_from|toio seems to not do anything nefarious with > locks we just need to open code get_pfn and follow_pfn and make sure > we drop the locks only after we've done. The write function also needs > the copy_from_user move, since we can't take userspace faults while > holding the mmap sem. >=20 > Signed-off-by: Daniel Vetter > Cc: Jason Gunthorpe > Cc: Dan Williams > Cc: Kees Cook > Cc: Andrew Morton > Cc: John Hubbard > Cc: J=C3=A9r=C3=B4me Glisse > Cc: Jan Kara > Cc: Dan Williams > Cc: linux-mm@kvack.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-samsung-soc@vger.kernel.org > Cc: linux-media@vger.kernel.org > Cc: Niklas Schnelle > Cc: Gerald Schaefer > Cc: linux-s390@vger.kernel.org > --- > arch/s390/pci/pci_mmio.c | 98 +++++++++++++++++++++++----------------- > 1 file changed, 57 insertions(+), 41 deletions(-) Looks good, thanks. Also survived some basic function test. Only some minor nitpick, see below. Reviewed-by: Gerald Schaefer >=20 > diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c > index 401cf670a243..4d194cb09372 100644 > --- a/arch/s390/pci/pci_mmio.c > +++ b/arch/s390/pci/pci_mmio.c > @@ -119,33 +119,15 @@ static inline int __memcpy_toio_inuser(void __iomem= *dst, > return rc; > } > =20 > -static long get_pfn(unsigned long user_addr, unsigned long access, > - unsigned long *pfn) > -{ > - struct vm_area_struct *vma; > - long ret; > - > - mmap_read_lock(current->mm); > - ret =3D -EINVAL; > - vma =3D find_vma(current->mm, user_addr); > - if (!vma) > - goto out; > - ret =3D -EACCES; > - if (!(vma->vm_flags & access)) > - goto out; > - ret =3D follow_pfn(vma, user_addr, pfn); > -out: > - mmap_read_unlock(current->mm); > - return ret; > -} > - > SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, > const void __user *, user_buffer, size_t, length) > { > u8 local_buf[64]; > void __iomem *io_addr; > void *buf; > - unsigned long pfn; > + struct vm_area_struct *vma; > + pte_t *ptep; > + spinlock_t *ptl; > long ret; > =20 > if (!zpci_is_enabled()) > @@ -158,7 +140,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, m= mio_addr, > * We only support write access to MIO capable devices if we are on > * a MIO enabled system. Otherwise we would have to check for every > * address if it is a special ZPCI_ADDR and would have to do > - * a get_pfn() which we don't need for MIO capable devices. Currently > + * a pfn lookup which we don't need for MIO capable devices. Currently > * ISM devices are the only devices without MIO support and there is no > * known need for accessing these from userspace. > */ > @@ -176,21 +158,37 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long,= mmio_addr, > } else > buf =3D local_buf; > =20 > - ret =3D get_pfn(mmio_addr, VM_WRITE, &pfn); > + ret =3D -EFAULT; > + if (copy_from_user(buf, user_buffer, length)) > + goto out_free; > + > + mmap_read_lock(current->mm); > + ret =3D -EINVAL; > + vma =3D find_vma(current->mm, mmio_addr); > + if (!vma) > + goto out_unlock_mmap; > + ret =3D -EACCES; > + if (!(vma->vm_flags & VM_WRITE)) > + goto out_unlock_mmap; > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) > + goto out_unlock_mmap; That check for VM_IO | VM_PFNMAP was previously hidden inside follow_pfn(), and that would have returned -EINVAL in this case. With your change, we now return -EACCES. Not sure how important that is, but it feels wrong. Maybe move the VM_IO | VM_PFNMAP check up, before the ret =3D -EACCES? [...] > @@ -306,22 +306,38 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, = mmio_addr, > buf =3D local_buf; > } > =20 > - ret =3D get_pfn(mmio_addr, VM_READ, &pfn); > + mmap_read_lock(current->mm); > + ret =3D -EINVAL; > + vma =3D find_vma(current->mm, mmio_addr); > + if (!vma) > + goto out_unlock_mmap; > + ret =3D -EACCES; > + if (!(vma->vm_flags & VM_WRITE)) > + goto out_unlock_mmap; > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) > + goto out_unlock_mmap; Same here with VM_IO | VM_PFNMAP and -EINVAL.