On 12/16/22 8:18 AM, Hao Sun wrote:
On 16 Dec 2022, at 3:03 PM, Yonghong Song <yhs@xxxxxxxx> 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@xxxxxxxxx>
---
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
