Messages in this thread | | | Subject | Re: [PATCH bpf-next] bpf: dup xlated insns with kvmalloc+memcpy | From | Daniel Borkmann <> | Date | Fri, 16 Dec 2022 16:24:31 +0100 |
| |
On 12/16/22 8:18 AM, Hao Sun wrote: > > >> On 16 Dec 2022, at 3:03 PM, Yonghong Song <yhs@meta.com> wrote: >> >> >> >> On 12/15/22 9:54 PM, Hao Sun wrote: >>> Currently, kmemdup() is used for allocating and copying xlated insns >>> in bpf_insn_prepare_dump(). The following warning can be triggered >>> when dup large amount of insns (roughly BPF_COMPLEXITY_LIMIT_INSNS/2) >>> because kmemdup() uses kmalloc() which would fail when allocing size >>> is too big, leading to failure in dump xlated insns: >>> WARNING: CPU: 2 PID: 7060 at mm/page_alloc.c:5534 >>> Call Trace: >>> <TASK> >>> __alloc_pages_node include/linux/gfp.h:237 [inline] >>> alloc_pages_node include/linux/gfp.h:260 [inline] >>> __kmalloc_large_node+0x81/0x160 mm/slab_common.c:1096 >>> __do_kmalloc_node mm/slab_common.c:943 [inline] >>> __kmalloc_node_track_caller.cold+0x5/0x5d mm/slab_common.c:975 >>> kmemdup+0x29/0x60 mm/util.c:129 >>> kmemdup include/linux/fortify-string.h:585 [inline] >>> bpf_insn_prepare_dump kernel/bpf/syscall.c:3820 [inline] >>> bpf_prog_get_info_by_fd+0x9a3/0x2cb0 kernel/bpf/syscall.c:3975 >>> bpf_obj_get_info_by_fd kernel/bpf/syscall.c:4297 [inline] >>> __sys_bpf+0x3928/0x56f0 kernel/bpf/syscall.c:5004 >>> __do_sys_bpf kernel/bpf/syscall.c:5069 [inline] >>> __se_sys_bpf kernel/bpf/syscall.c:5067 [inline] >>> ... >>> So use kvmalloc()+memcpy() to fix this, for small size of insns, >>> this is same as kmemdup(), but this also support dup large amount >>> of xlated insns. >>> Signed-off-by: Hao Sun <sunhao.th@gmail.com> >>> --- >>> kernel/bpf/syscall.c | 8 ++++---- >>> 1 file changed, 4 insertions(+), 4 deletions(-) >>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >>> index 35972afb6850..06229fddac0d 100644 >>> --- a/kernel/bpf/syscall.c >>> +++ b/kernel/bpf/syscall.c >>> @@ -3831,10 +3831,10 @@ static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog, >>> u8 code; >>> int i; >>> - insns = kmemdup(prog->insnsi, bpf_prog_insn_size(prog), >>> - GFP_USER); >> >> Does kmemdup(prog->insnsi, bpf_prog_insn_size(prog), GFP_USER | __GFP_NOWARN) work? > > This only suppress the warning, bpf_insn_prepare_dump() still fails because of > the failure of kmalloc() invoked by kmemdup().
Ok, instead of open coding, would be nice if we add a helper to mm/util.c :
void *kvmemdup(const void *src, size_t len, gfp_t gfp) { void *p;
p = kvmalloc(len, gfp); if (p) memcpy(p, src, len); return p; } EXPORT_SYMBOL(kvmemdup);
And then bpf and in future others could make use of it.
Thanks, Daniel
| |