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

[ Upstream commit 87338c8e2cbb317b5f757e6172f94e2e3799cd20 ]

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: 156d0e290e96 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index a66e64b..5d115bd 100644 (file)
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -762,7 +762,8 @@ emit_clear:
                        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);
@@ -771,7 +772,8 @@ emit_clear:
                        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);