Commit 87338c8e authored Dec 14, 2017 by Daniel Borkmann Committed by Alexei Starovoitov Dec 15, 2017

bpf, ppc64: do not reload skb pointers in non-skb context



The assumption of unconditionally reloading skb pointers on
BPF helper calls where bpf_helper_changes_pkt_data() holds
true is wrong. There can be different contexts where the helper
would enforce a reload such as in case of XDP. Here, we do
have a struct xdp_buff instead of struct sk_buff as context,
thus this will access garbage.

JITs only ever need to deal with cached skb pointer reload
when ld_abs/ind was seen, therefore guard the reload behind
SEEN_SKB.

Fixes: 156d0e29 ("powerpc/ebpf/jit: Implement JIT compiler for extended BPF")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

parent 6d59b7db

arch/powerpc/net/bpf_jit_comp64.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -763,7 +763,8 @@ static int bpf_jit_build_body(struct bpf_prog fp, u32 image,
		func = (u8 *) __bpf_call_base + imm;

		/* Save skb pointer if we need to re-cache skb data */
		if (bpf_helper_changes_pkt_data(func))
		if ((ctx->seen & SEEN_SKB) &&
		bpf_helper_changes_pkt_data(func))
		PPC_BPF_STL(3, 1, bpf_jit_stack_local(ctx));

		bpf_jit_emit_func_call(image, ctx, (u64)func);
		@@ -772,7 +773,8 @@ static int bpf_jit_build_body(struct bpf_prog fp, u32 image,
		PPC_MR(b2p[BPF_REG_0], 3);

		/* refresh skb cache */
		if (bpf_helper_changes_pkt_data(func)) {
		if ((ctx->seen & SEEN_SKB) &&
		bpf_helper_changes_pkt_data(func)) {
		/* reload skb pointer to r3 */
		PPC_BPF_LL(3, 1, bpf_jit_stack_local(ctx));
		bpf_jit_emit_skb_loads(image, ctx);