On Mon, Oct 31, 2022 at 02:58:30PM -0700, Song Liu wrote: > vmalloc_exec is used to allocate memory to host dynamic kernel text > (modules, BPF programs, etc.) with huge pages. This is similar to the > proposal by Peter in [1]. > > A new tree of vmap_area, free_text_area_* tree, is introduced in addition > to free_vmap_area_* and vmap_area_*. vmalloc_exec allocates pages from > free_text_area_*. When there isn't enough space left in free_text_area_*, > new PMD_SIZE page(s) is allocated from free_vmap_area_* and added to > free_text_area_*. To be more accurate, the vmap_area is first added to > vmap_area_* tree and then moved to free_text_area_*. This extra move > simplifies the logic of vmalloc_exec. > > vmap_area in free_text_area_* tree are backed with memory, but we need > subtree_max_size for tree operations. Therefore, vm_struct for these > vmap_area are stored in a separate list, all_text_vm. > > The new tree allows separate handling of < PAGE_SIZE allocations, as > current vmalloc code mostly assumes PAGE_SIZE aligned allocations. This > version of vmalloc_exec can handle bpf programs, which uses 64 byte > aligned allocations), and modules, which uses PAGE_SIZE aligned > allocations. > > Memory allocated by vmalloc_exec() is set to RO+X before returning to the > caller. Therefore, the caller cannot write directly write to the memory. > Instead, the caller is required to use vcopy_exec() to update the memory. > For the safety and security of X memory, vcopy_exec() checks the data > being updated always in the memory allocated by one vmalloc_exec() call. > vcopy_exec() uses text_poke like mechanism and requires arch support. > Specifically, the arch need to implement arch_vcopy_exec(). > > In vfree_exec(), the memory is first erased with arch_invalidate_exec(). > Then, the memory is added to free_text_area_*. If this free creates big > enough continuous free space (> PMD_SIZE), vfree_exec() will try to free > the backing vm_struct. > > [1] https://lore.kernel.org/bpf/Ys6cWUMHO8XwyYgr@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > Signed-off-by: Song Liu <song@xxxxxxxxxx> > --- > include/linux/vmalloc.h | 5 + > mm/nommu.c | 12 ++ > mm/vmalloc.c | 318 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 335 insertions(+) > > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h > index 096d48aa3437..9b2042313c12 100644 > --- a/include/linux/vmalloc.h > +++ b/include/linux/vmalloc.h > @@ -154,6 +154,11 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align, > void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask, > int node, const void *caller) __alloc_size(1); > void *vmalloc_huge(unsigned long size, gfp_t gfp_mask) __alloc_size(1); > +void *vmalloc_exec(unsigned long size, unsigned long align) __alloc_size(1); > +void *vcopy_exec(void *dst, void *src, size_t len); > +void vfree_exec(void *addr); > +void *arch_vcopy_exec(void *dst, void *src, size_t len); > +int arch_invalidate_exec(void *ptr, size_t len); > > extern void *__vmalloc_array(size_t n, size_t size, gfp_t flags) __alloc_size(1, 2); > extern void *vmalloc_array(size_t n, size_t size) __alloc_size(1, 2); > diff --git a/mm/nommu.c b/mm/nommu.c > index 214c70e1d059..8a1317247ef0 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -371,6 +371,18 @@ int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages, > } > EXPORT_SYMBOL(vm_map_pages_zero); > > +void *vmalloc_exec(unsigned long size, unsigned long align) > +{ > + return NULL; > +} > + > +void *vcopy_exec(void *dst, void *src, size_t len) > +{ > + return ERR_PTR(-EOPNOTSUPP); > +} > + > +void vfree_exec(const void *addr) { } > + > /* > * sys_brk() for the most part doesn't need the global kernel > * lock, except when an application is doing something nasty > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index ccaa461998f3..6f4c73e67191 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -72,6 +72,9 @@ early_param("nohugevmalloc", set_nohugevmalloc); > static const bool vmap_allow_huge = false; > #endif /* CONFIG_HAVE_ARCH_HUGE_VMALLOC */ > > +#define PMD_ALIGN(addr) ALIGN(addr, PMD_SIZE) > +#define PMD_ALIGN_DOWN(addr) ALIGN_DOWN(addr, PMD_SIZE) > + > bool is_vmalloc_addr(const void *x) > { > unsigned long addr = (unsigned long)kasan_reset_tag(x); > @@ -769,6 +772,38 @@ static LIST_HEAD(free_vmap_area_list); > */ > static struct rb_root free_vmap_area_root = RB_ROOT; > > +/* > + * free_text_area for vmalloc_exec() > + */ > +static DEFINE_SPINLOCK(free_text_area_lock); > +/* > + * This linked list is used in pair with free_text_area_root. > + * It gives O(1) access to prev/next to perform fast coalescing. > + */ > +static LIST_HEAD(free_text_area_list); > + > +/* > + * This augment red-black tree represents the free text space. > + * All vmap_area objects in this tree are sorted by va->va_start > + * address. It is used for allocation and merging when a vmap > + * object is released. > + * > + * Each vmap_area node contains a maximum available free block > + * of its sub-tree, right or left. Therefore it is possible to > + * find a lowest match of free area. > + * > + * vmap_area in this tree are backed by RO+X memory, but they do > + * not have valid vm pointer (because we need subtree_max_size). > + * The vm for these vmap_area are stored in all_text_vm. > + */ > +static struct rb_root free_text_area_root = RB_ROOT; > + > +/* > + * List of vm_struct for free_text_area_root. This list is rarely > + * accessed, so the O(N) complexity is not likely a real issue. > + */ > +struct vm_struct *all_text_vm; > + > /* > * Preload a CPU with one object for "no edge" split case. The > * aim is to get rid of allocations from the atomic context, thus > @@ -3313,6 +3348,289 @@ void *vmalloc(unsigned long size) > } > EXPORT_SYMBOL(vmalloc); > > +#if defined(CONFIG_MODULES) && defined(MODULES_VADDR) > +#define VMALLOC_EXEC_START MODULES_VADDR > +#define VMALLOC_EXEC_END MODULES_END > +#else > +#define VMALLOC_EXEC_START VMALLOC_START > +#define VMALLOC_EXEC_END VMALLOC_END > +#endif > + > +static void move_vmap_to_free_text_tree(void *addr) > +{ > + struct vmap_area *va; > + > + /* remove from vmap_area_root */ > + spin_lock(&vmap_area_lock); > + va = __find_vmap_area((unsigned long)addr, &vmap_area_root); > + if (WARN_ON_ONCE(!va)) { > + spin_unlock(&vmap_area_lock); > + return; > + } > + unlink_va(va, &vmap_area_root); > + spin_unlock(&vmap_area_lock); > + > + /* make the memory RO+X */ > + memset(addr, 0, va->va_end - va->va_start); > + set_memory_ro(va->va_start, (va->va_end - va->va_start) >> PAGE_SHIFT); > + set_memory_x(va->va_start, (va->va_end - va->va_start) >> PAGE_SHIFT); > + > + /* add to all_text_vm */ > + va->vm->next = all_text_vm; > + all_text_vm = va->vm; > + > + /* add to free_text_area_root */ > + spin_lock(&free_text_area_lock); > + merge_or_add_vmap_area_augment(va, &free_text_area_root, &free_text_area_list); > + spin_unlock(&free_text_area_lock); > +} > + > +/** > + * vmalloc_exec - allocate virtually contiguous RO+X memory > + * @size: allocation size > + * > + * This is used to allocate dynamic kernel text, such as module text, BPF > + * programs, etc. User need to use text_poke to update the memory allocated > + * by vmalloc_exec. > + * > + * Return: pointer to the allocated memory or %NULL on error > + */ > +void *vmalloc_exec(unsigned long size, unsigned long align) > +{ > + struct vmap_area *va, *tmp; > + unsigned long addr; > + enum fit_type type; > + int ret; > + > + va = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, NUMA_NO_NODE); > + if (unlikely(!va)) > + return NULL; > + > +again: > + preload_this_cpu_lock(&free_text_area_lock, GFP_KERNEL, NUMA_NO_NODE); > + tmp = find_vmap_lowest_match(&free_text_area_root, size, align, 1, false); > + > + if (!tmp) { > + unsigned long alloc_size; > + void *ptr; > + > + spin_unlock(&free_text_area_lock); > + > + /* > + * Not enough continuous space in free_text_area_root, try > + * allocate more memory. The memory is first added to > + * vmap_area_root, and then moved to free_text_area_root. > + */ > + alloc_size = roundup(size, PMD_SIZE * num_online_nodes()); > + ptr = __vmalloc_node_range(alloc_size, PMD_SIZE, VMALLOC_EXEC_START, > + VMALLOC_EXEC_END, GFP_KERNEL, PAGE_KERNEL, > + VM_ALLOW_HUGE_VMAP | VM_NO_GUARD, > + NUMA_NO_NODE, __builtin_return_address(0)); > + if (unlikely(!ptr)) > + goto err_out; > + > + move_vmap_to_free_text_tree(ptr); > + goto again; > It is yet another allocator built on top of vmalloc. So there are 4 then. Could you please avoid of doing it? I do not find it as something that is reasonable. -- Uladzislau Rezki
