kernel/linux.git/include/linux/bpf.h, branch linux-6.9.y

bpf: support deferring bpf_link dealloc to after RCU grace period

2024-03-29T01:47:45+00:00

BPF link for some program types is passed as a "context" which can be used by those BPF programs to look up additional information. E.g., for multi-kprobes and multi-uprobes, link is used to fetch BPF cookie values. Because of this runtime dependency, when bpf_link refcnt drops to zero there could still be active BPF programs running accessing link data. This patch adds generic support to defer bpf_link dealloc callback to after RCU GP, if requested. This is done by exposing two different deallocation callbacks, one synchronous and one deferred. If deferred one is provided, bpf_link_free() will schedule dealloc_deferred() callback to happen after RCU GP. BPF is using two flavors of RCU: "classic" non-sleepable one and RCU tasks trace one. The latter is used when sleepable BPF programs are used. bpf_link_free() accommodates that by checking underlying BPF program's sleepable flag, and goes either through normal RCU GP only for non-sleepable, or through RCU tasks trace GP *and* then normal RCU GP (taking into account rcu_trace_implies_rcu_gp() optimization), if BPF program is sleepable. We use this for multi-kprobe and multi-uprobe links, which dereference link during program run. We also preventively switch raw_tp link to use deferred dealloc callback, as upcoming changes in bpf-next tree expose raw_tp link data (specifically, cookie value) to BPF program at runtime as well. Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link") Reported-by: syzbot+981935d9485a560bfbcb@syzkaller.appspotmail.com Reported-by: syzbot+2cb5a6c573e98db598cc@syzkaller.appspotmail.com Reported-by: syzbot+62d8b26793e8a2bd0516@syzkaller.appspotmail.com Signed-off-by: Andrii Nakryiko Acked-by: Jiri Olsa Link: https://lore.kernel.org/r/20240328052426.3042617-2-andrii@kernel.org Signed-off-by: Alexei Starovoitov

bpf: move sleepable flag from bpf_prog_aux to bpf_prog

2024-03-11T23:41:25+00:00

prog->aux->sleepable is checked very frequently as part of (some) BPF program run hot paths. So this extra aux indirection seems wasteful and on busy systems might cause unnecessary memory cache misses. Let's move sleepable flag into prog itself to eliminate unnecessary pointer dereference. Signed-off-by: Andrii Nakryiko Acked-by: Jiri Olsa Message-ID: <20240309004739.2961431-1-andrii@kernel.org> Signed-off-by: Alexei Starovoitov

bpf: Recognize btf_decl_tag("arg: Arena") as PTR_TO_ARENA.

2024-03-11T22:37:24+00:00

In global bpf functions recognize btf_decl_tag("arg:arena") as PTR_TO_ARENA. Note, when the verifier sees: __weak void foo(struct bar *p) it recognizes 'p' as PTR_TO_MEM and 'struct bar' has to be a struct with scalars. Hence the only way to use arena pointers in global functions is to tag them with "arg:arena". Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Acked-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/bpf/20240308010812.89848-7-alexei.starovoitov@gmail.com

bpf: Recognize addr_space_cast instruction in the verifier.

2024-03-11T22:37:24+00:00

rY = addr_space_cast(rX, 0, 1) tells the verifier that rY->type = PTR_TO_ARENA. Any further operations on PTR_TO_ARENA register have to be in 32-bit domain. The verifier will mark load/store through PTR_TO_ARENA with PROBE_MEM32. JIT will generate them as kern_vm_start + 32bit_addr memory accesses. rY = addr_space_cast(rX, 1, 0) tells the verifier that rY->type = unknown scalar. If arena->map_flags has BPF_F_NO_USER_CONV set then convert cast_user to mov32 as well. Otherwise JIT will convert it to: rY = (u32)rX; if (rY) rY |= arena->user_vm_start & ~(u64)~0U; Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240308010812.89848-6-alexei.starovoitov@gmail.com

bpf: Add x86-64 JIT support for PROBE_MEM32 pseudo instructions.

2024-03-11T22:37:24+00:00

Add support for [LDX | STX | ST], PROBE_MEM32, [B | H | W | DW] instructions. They are similar to PROBE_MEM instructions with the following differences: - PROBE_MEM has to check that the address is in the kernel range with src_reg + insn->off >= TASK_SIZE_MAX + PAGE_SIZE check - PROBE_MEM doesn't support store - PROBE_MEM32 relies on the verifier to clear upper 32-bit in the register - PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in %r12 in the prologue) Due to bpf_arena constructions such %r12 + %reg + off16 access is guaranteed to be within arena virtual range, so no address check at run-time. - PROBE_MEM32 allows STX and ST. If they fault the store is a nop. When LDX faults the destination register is zeroed. Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Acked-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/bpf/20240308010812.89848-4-alexei.starovoitov@gmail.com

bpf: Introduce bpf_arena.

2024-03-11T22:37:23+00:00

Introduce bpf_arena, which is a sparse shared memory region between the bpf program and user space. Use cases: 1. User space mmap-s bpf_arena and uses it as a traditional mmap-ed anonymous region, like memcached or any key/value storage. The bpf program implements an in-kernel accelerator. XDP prog can search for a key in bpf_arena and return a value without going to user space. 2. The bpf program builds arbitrary data structures in bpf_arena (hash tables, rb-trees, sparse arrays), while user space consumes it. 3. bpf_arena is a "heap" of memory from the bpf program's point of view. The user space may mmap it, but bpf program will not convert pointers to user base at run-time to improve bpf program speed. Initially, the kernel vm_area and user vma are not populated. User space can fault in pages within the range. While servicing a page fault, bpf_arena logic will insert a new page into the kernel and user vmas. The bpf program can allocate pages from that region via bpf_arena_alloc_pages(). This kernel function will insert pages into the kernel vm_area. The subsequent fault-in from user space will populate that page into the user vma. The BPF_F_SEGV_ON_FAULT flag at arena creation time can be used to prevent fault-in from user space. In such a case, if a page is not allocated by the bpf program and not present in the kernel vm_area, the user process will segfault. This is useful for use cases 2 and 3 above. bpf_arena_alloc_pages() is similar to user space mmap(). It allocates pages either at a specific address within the arena or allocates a range with the maple tree. bpf_arena_free_pages() is analogous to munmap(), which frees pages and removes the range from the kernel vm_area and from user process vmas. bpf_arena can be used as a bpf program "heap" of up to 4GB. The speed of bpf program is more important than ease of sharing with user space. This is use case 3. In such a case, the BPF_F_NO_USER_CONV flag is recommended. It will tell the verifier to treat the rX = bpf_arena_cast_user(rY) instruction as a 32-bit move wX = wY, which will improve bpf prog performance. Otherwise, bpf_arena_cast_user is translated by JIT to conditionally add the upper 32 bits of user vm_start (if the pointer is not NULL) to arena pointers before they are stored into memory. This way, user space sees them as valid 64-bit pointers. Diff https://github.com/llvm/llvm-project/pull/84410 enables LLVM BPF backend generate the bpf_addr_space_cast() instruction to cast pointers between address_space(1) which is reserved for bpf_arena pointers and default address space zero. All arena pointers in a bpf program written in C language are tagged as __attribute__((address_space(1))). Hence, clang provides helpful diagnostics when pointers cross address space. Libbpf and the kernel support only address_space == 1. All other address space identifiers are reserved. rX = bpf_addr_space_cast(rY, /* dst_as */ 1, /* src_as */ 0) tells the verifier that rX->type = PTR_TO_ARENA. Any further operations on PTR_TO_ARENA register have to be in the 32-bit domain. The verifier will mark load/store through PTR_TO_ARENA with PROBE_MEM32. JIT will generate them as kern_vm_start + 32bit_addr memory accesses. The behavior is similar to copy_from_kernel_nofault() except that no address checks are necessary. The address is guaranteed to be in the 4GB range. If the page is not present, the destination register is zeroed on read, and the operation is ignored on write. rX = bpf_addr_space_cast(rY, 0, 1) tells the verifier that rX->type = unknown scalar. If arena->map_flags has BPF_F_NO_USER_CONV set, then the verifier converts such cast instructions to mov32. Otherwise, JIT will emit native code equivalent to: rX = (u32)rY; if (rY) rX |= clear_lo32_bits(arena->user_vm_start); /* replace hi32 bits in rX */ After such conversion, the pointer becomes a valid user pointer within bpf_arena range. The user process can access data structures created in bpf_arena without any additional computations. For example, a linked list built by a bpf program can be walked natively by user space. Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Reviewed-by: Barret Rhoden Link: https://lore.kernel.org/bpf/20240308010812.89848-2-alexei.starovoitov@gmail.com

bpf: Plumb get_unmapped_area() callback into bpf_map_ops

2024-03-07T22:58:48+00:00

Subsequent patches introduce bpf_arena that imposes special alignment requirements on address selection. Acked-by: Kumar Kartikeya Dwivedi Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/r/20240307031228.42896-4-alexei.starovoitov@gmail.com Signed-off-by: Martin KaFai Lau

bpf: struct_ops supports more than one page for trampolines.

2024-03-04T22:09:20+00:00

The BPF struct_ops previously only allowed one page of trampolines. Each function pointer of a struct_ops is implemented by a struct_ops bpf program. Each struct_ops bpf program requires a trampoline. The following selftest patch shows each page can hold a little more than 20 trampolines. While one page is more than enough for the tcp-cc usecase, the sched_ext use case shows that one page is not always enough and hits the one page limit. This patch overcomes the one page limit by allocating another page when needed and it is limited to a total of MAX_IMAGE_PAGES (8) pages which is more than enough for reasonable usages. The variable st_map->image has been changed to st_map->image_pages, and its type has been changed to an array of pointers to pages. Signed-off-by: Kui-Feng Lee Link: https://lore.kernel.org/r/20240224223418.526631-3-thinker.li@gmail.com Signed-off-by: Martin KaFai Lau

bpf: Shrink size of struct bpf_map/bpf_array.

2024-02-21T21:49:14+00:00

Back in 2018 the commit be95a845cc44 ("bpf: avoid false sharing of map refcount with max_entries") added ____cacheline_aligned to "struct bpf_map" to make sure that fields like refcnt don't share a cache line with max_entries that is used to bounds check map access. That was done to make spectre style attacks harder. The main mitigation is done via code similar to array_index_nospec(), of course. This was an additional precaution. It increased the size of "struct bpf_map" a little, but it's affect on all other maps (like array) is significant, since "struct bpf_map" is typically the first member in other map types. Undo this ____cacheline_aligned tag. Instead move freeze_mutex field around, so that refcnt and max_entries are still in different cache lines. The main effect is seen in sizeof(struct bpf_array) that reduces from 320 to 248 bytes. BEFORE: struct bpf_map { const struct bpf_map_ops * ops; /* 0 8 */ ... char name[16]; /* 96 16 */ /* XXX 16 bytes hole, try to pack */ /* --- cacheline 2 boundary (128 bytes) --- */ atomic64_t refcnt __attribute__((__aligned__(64))); /* 128 8 */ ... /* size: 256, cachelines: 4, members: 30 */ /* sum members: 232, holes: 1, sum holes: 16 */ /* padding: 8 */ /* paddings: 1, sum paddings: 2 */ } __attribute__((__aligned__(64))); struct bpf_array { struct bpf_map map; /* 0 256 */ ... /* size: 320, cachelines: 5, members: 5 */ /* padding: 48 */ /* paddings: 1, sum paddings: 8 */ } __attribute__((__aligned__(64))); AFTER: struct bpf_map { /* size: 232, cachelines: 4, members: 30 */ /* paddings: 1, sum paddings: 2 */ /* last cacheline: 40 bytes */ }; struct bpf_array { /* size: 248, cachelines: 4, members: 5 */ /* last cacheline: 56 bytes */ }; Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20240220235001.57411-1-alexei.starovoitov@gmail.com

bpf: Create argument information for nullable arguments.

2024-02-13T23:16:44+00:00

Collect argument information from the type information of stub functions to mark arguments of BPF struct_ops programs with PTR_MAYBE_NULL if they are nullable. A nullable argument is annotated by suffixing "__nullable" at the argument name of stub function. For nullable arguments, this patch sets a struct bpf_ctx_arg_aux to label their reg_type with PTR_TO_BTF_ID | PTR_TRUSTED | PTR_MAYBE_NULL. This makes the verifier to check programs and ensure that they properly check the pointer. The programs should check if the pointer is null before accessing the pointed memory. The implementer of a struct_ops type should annotate the arguments that can be null. The implementer should define a stub function (empty) as a placeholder for each defined operator. The name of a stub function should be in the pattern "__". For example, for test_maybe_null of struct bpf_testmod_ops, it's stub function name should be "bpf_testmod_ops__test_maybe_null". You mark an argument nullable by suffixing the argument name with "__nullable" at the stub function. Since we already has stub functions for kCFI, we just reuse these stub functions with the naming convention mentioned earlier. These stub functions with the naming convention is only required if there are nullable arguments to annotate. For functions having not nullable arguments, stub functions are not necessary for the purpose of this patch. This patch will prepare a list of struct bpf_ctx_arg_aux, aka arg_info, for each member field of a struct_ops type. "arg_info" will be assigned to "prog->aux->ctx_arg_info" of BPF struct_ops programs in check_struct_ops_btf_id() so that it can be used by btf_ctx_access() later to set reg_type properly for the verifier. Signed-off-by: Kui-Feng Lee Link: https://lore.kernel.org/r/20240209023750.1153905-4-thinker.li@gmail.com Signed-off-by: Martin KaFai Lau