linux-kernel - [PATCH bpf-next] bpf: dup xlated insns with kvmalloc+memcpy

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Date:   Fri, 16 Dec 2022 13:54:35 +0800
From:   Hao Sun <sunhao.th@...il.com>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, Hao Sun <sunhao.th@...il.com>
Subject: [PATCH bpf-next] bpf: dup xlated insns with kvmalloc+memcpy

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@...il.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);
-	if (!insns)
+	insns = kvmalloc(bpf_prog_insn_size(prog), GFP_USER | __GFP_NOWARN);
+	if (unlikely(!insns))
 		return insns;
+	memcpy(insns, prog->insnsi, bpf_prog_insn_size(prog));

 	for (i = 0; i < prog->len; i++) {
 		code = insns[i].code;
@@ -3992,7 +3992,7 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 		uinsns = u64_to_user_ptr(info.xlated_prog_insns);
 		ulen = min_t(u32, info.xlated_prog_len, ulen);
 		fault = copy_to_user(uinsns, insns_sanitized, ulen);
-		kfree(insns_sanitized);
+		kvfree(insns_sanitized);
 		if (fault)
 			return -EFAULT;
 	}

base-commit: 0e43662e61f2569500ab83b8188c065603530785
-- 
2.39.0