On Fri, Sep 16, 2022 at 09:38:33AM +0100, Matthew Wilcox wrote: > On Thu, Sep 15, 2022 at 05:59:56PM -0600, Yu Zhao wrote: > > I think this is a manifest of the lockdep warning I reported a couple > > of weeks ago: > > https://lore.kernel.org/r/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@xxxxxxxxxxxxxx/ > > That would certainly match the symptoms. > > Turning vmap_lock into an NMI-safe lock would be bad. I don't even know > if we have primitives for that (it's not like you can disable an NMI > ...) > > I don't quite have time to write a patch right now. Perhaps something > like: > > struct vmap_area *find_vmap_area_nmi(unsigned long addr) > { > struct vmap_area *va; > > if (spin_trylock(&vmap_area_lock)) > return NULL; > va = __find_vmap_area(addr, &vmap_area_root); > spin_unlock(&vmap_area_lock); > > return va; > } > > and then call find_vmap_area_nmi() in check_heap_object(). I may have > the polarity of the return value of spin_trylock() incorrect. I think we'll need something slightly tweaked, since this would return NULL under any contention (and a NULL return is fatal in check_heap_object()). It seems like we need to explicitly check for being in nmi context in check_heap_object() to deal with it? Like this (only build tested): diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index 096d48aa3437..c8a00f181a11 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -216,6 +216,7 @@ void free_vm_area(struct vm_struct *area); extern struct vm_struct *remove_vm_area(const void *addr); extern struct vm_struct *find_vm_area(const void *addr); struct vmap_area *find_vmap_area(unsigned long addr); +struct vmap_area *find_vmap_area_try(unsigned long addr); static inline bool is_vm_area_hugepages(const void *addr) { diff --git a/mm/usercopy.c b/mm/usercopy.c index c1ee15a98633..9f943c29e7ec 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -173,7 +173,16 @@ static inline void check_heap_object(const void *ptr, unsigned long n, } if (is_vmalloc_addr(ptr)) { - struct vmap_area *area = find_vmap_area(addr); + struct vmap_area *area; + + if (!in_nmi()) { + area = find_vmap_area(addr); + } else { + area = find_vmap_area_try(addr); + /* Give up under NMI to avoid deadlocks. */ + if (!area) + return; + } if (!area) usercopy_abort("vmalloc", "no area", to_user, 0, n); diff --git a/mm/vmalloc.c b/mm/vmalloc.c index dd6cdb201195..f14f1902c2f6 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1840,6 +1840,17 @@ struct vmap_area *find_vmap_area(unsigned long addr) return va; } +struct vmap_area *find_vmap_area_try(unsigned long addr) +{ + struct vmap_area *va = NULL; + + if (spin_trylock(&vmap_area_lock)) { + va = __find_vmap_area(addr, &vmap_area_root); + spin_unlock(&vmap_area_lock); + } + return va; +} + /*** Per cpu kva allocator ***/ /* -- Kees Cook
