| Message ID | 20201026105818.2585306-9-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | follow_pfn and other iomap races | expand |
> +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, > + unsigned long *pfn) The one tab indent here looks weird, normally tis would be two tabs or aligned aftetthe opening brace. > +{ > +#ifdef CONFIG_STRICT_FOLLOW_PFN > + pr_info("unsafe follow_pfn usage rejected, see CONFIG_STRICT_FOLLOW_PFN\n"); > + return -EINVAL; > +#else > + WARN_ONCE(1, "unsafe follow_pfn usage\n"); > + add_taint(TAINT_USER, LOCKDEP_STILL_OK); > + > + return follow_pfn(vma, address, pfn); > +#endif Woudn't this be a pretty good use case of "if (IS_ENABLED(...)))"? Also I'd expect the inverse polarity of the config option, that is a USAFE_FOLLOW_PFN option to enable to unsafe behavior. > +/** > + * unsafe_follow_pfn - look up PFN at a user virtual address > + * @vma: memory mapping > + * @address: user virtual address > + * @pfn: location to store found PFN > + * > + * Only IO mappings and raw PFN mappings are allowed. > + * > + * Returns zero and the pfn at @pfn on success, -ve otherwise. > + */ > +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, > + unsigned long *pfn) > +{ > + return follow_pfn(vma, address, pfn); > +} > +EXPORT_SYMBOL(unsafe_follow_pfn); Any reason this doesn't use the warn and disable logic?
On Thu, Oct 29, 2020 at 9:56 AM Christoph Hellwig <hch@infradead.org> wrote: > > > +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, > > + unsigned long *pfn) > > The one tab indent here looks weird, normally tis would be two tabs > or aligned aftetthe opening brace. > > > +{ > > +#ifdef CONFIG_STRICT_FOLLOW_PFN > > + pr_info("unsafe follow_pfn usage rejected, see CONFIG_STRICT_FOLLOW_PFN\n"); > > + return -EINVAL; > > +#else > > + WARN_ONCE(1, "unsafe follow_pfn usage\n"); > > + add_taint(TAINT_USER, LOCKDEP_STILL_OK); > > + > > + return follow_pfn(vma, address, pfn); > > +#endif > > Woudn't this be a pretty good use case of "if (IS_ENABLED(...)))"? > > Also I'd expect the inverse polarity of the config option, that is > a USAFE_FOLLOW_PFN option to enable to unsafe behavior. Was just about to send out v5, will apply your suggestions for that using IS_ENABLED. Wrt negative or positive Kconfig, I was following STRICT_DEVMEM symbol as precedence. But easy to invert if there's strong feeling the other way round, I'm not attached to either. > > +/** > > + * unsafe_follow_pfn - look up PFN at a user virtual address > > + * @vma: memory mapping > > + * @address: user virtual address > > + * @pfn: location to store found PFN > > + * > > + * Only IO mappings and raw PFN mappings are allowed. > > + * > > + * Returns zero and the pfn at @pfn on success, -ve otherwise. > > + */ > > +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, > > + unsigned long *pfn) > > +{ > > + return follow_pfn(vma, address, pfn); > > +} > > +EXPORT_SYMBOL(unsafe_follow_pfn); > > Any reason this doesn't use the warn and disable logic? I figured without an mmu there's not much guarantees anyway. But I guess I can put it in here too for consistency. -Daniel
diff --git a/include/linux/mm.h b/include/linux/mm.h index 2a16631c1fda..ec8c90928fc9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1653,6 +1653,8 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address, pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp); int follow_pfn(struct vm_area_struct *vma, unsigned long address, unsigned long *pfn); +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, + unsigned long *pfn); int follow_phys(struct vm_area_struct *vma, unsigned long address, unsigned int flags, unsigned long *prot, resource_size_t *phys); int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, diff --git a/mm/memory.c b/mm/memory.c index 1b46eae3b703..9a2ec07ff20b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4788,7 +4788,12 @@ EXPORT_SYMBOL(follow_pte_pmd); * @address: user virtual address * @pfn: location to store found PFN * - * Only IO mappings and raw PFN mappings are allowed. + * Only IO mappings and raw PFN mappings are allowed. Note that callers must + * ensure coherency with pte updates by using a &mmu_notifier to follow updates. + * If this is not feasible, or the access to the @pfn is only very short term, + * use follow_pte_pmd() instead and hold the pagetable lock for the duration of + * the access instead. Any caller not following these requirements must use + * unsafe_follow_pfn() instead. * * Return: zero and the pfn at @pfn on success, -ve otherwise. */ @@ -4811,6 +4816,31 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address, } EXPORT_SYMBOL(follow_pfn); +/** + * unsafe_follow_pfn - look up PFN at a user virtual address + * @vma: memory mapping + * @address: user virtual address + * @pfn: location to store found PFN + * + * Only IO mappings and raw PFN mappings are allowed. + * + * Returns zero and the pfn at @pfn on success, -ve otherwise. + */ +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, + unsigned long *pfn) +{ +#ifdef CONFIG_STRICT_FOLLOW_PFN + pr_info("unsafe follow_pfn usage rejected, see CONFIG_STRICT_FOLLOW_PFN\n"); + return -EINVAL; +#else + WARN_ONCE(1, "unsafe follow_pfn usage\n"); + add_taint(TAINT_USER, LOCKDEP_STILL_OK); + + return follow_pfn(vma, address, pfn); +#endif +} +EXPORT_SYMBOL(unsafe_follow_pfn); + #ifdef CONFIG_HAVE_IOREMAP_PROT int follow_phys(struct vm_area_struct *vma, unsigned long address, unsigned int flags, diff --git a/mm/nommu.c b/mm/nommu.c index 75a327149af1..3db2910f0d64 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -132,6 +132,23 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address, } EXPORT_SYMBOL(follow_pfn); +/** + * unsafe_follow_pfn - look up PFN at a user virtual address + * @vma: memory mapping + * @address: user virtual address + * @pfn: location to store found PFN + * + * Only IO mappings and raw PFN mappings are allowed. + * + * Returns zero and the pfn at @pfn on success, -ve otherwise. + */ +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, + unsigned long *pfn) +{ + return follow_pfn(vma, address, pfn); +} +EXPORT_SYMBOL(unsafe_follow_pfn); + LIST_HEAD(vmap_area_list); void vfree(const void *addr) diff --git a/security/Kconfig b/security/Kconfig index 7561f6f99f1d..48945402e103 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -230,6 +230,19 @@ config STATIC_USERMODEHELPER_PATH If you wish for all usermode helper programs to be disabled, specify an empty string here (i.e. ""). +config STRICT_FOLLOW_PFN + bool "Disable unsafe use of follow_pfn" + depends on MMU + help + Some functionality in the kernel follows userspace mappings to iomem + ranges in an unsafe matter. Examples include v4l userptr for zero-copy + buffers sharing. + + If this option is switched on, such access is rejected. Only enable + this option when you must run userspace which requires this. + + If in doubt, say Y. + source "security/selinux/Kconfig" source "security/smack/Kconfig" source "security/tomoyo/Kconfig"
Way back it was a reasonable assumptions that iomem mappings never change the pfn range they point at. But this has changed: - gpu drivers dynamically manage their memory nowadays, invalidating ptes with unmap_mapping_range when buffers get moved - 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) - 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") Accessing pfns obtained from ptes without holding all the locks is therefore no longer a good idea. Unfortunately there's some users where this is not fixable (like v4l userptr of iomem mappings) or involves a pile of work (vfio type1 iommu). For now annotate these as unsafe and splat appropriately. This patch adds an unsafe_follow_pfn, which later patches will then roll out to all appropriate places. Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kees Cook <keescook@chromium.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Dan Williams <dan.j.williams@intel.com> 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: kvm@vger.kernel.org Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> --- include/linux/mm.h | 2 ++ mm/memory.c | 32 +++++++++++++++++++++++++++++++- mm/nommu.c | 17 +++++++++++++++++ security/Kconfig | 13 +++++++++++++ 4 files changed, 63 insertions(+), 1 deletion(-)