bpf: Account for insn->off when doing bpf_probe_read_kernel

In the bpf interpreter mode, bpf_probe_read_kernel is used to read
from PTR_TO_BTF_ID's kernel object.  It currently missed considering
the insn->off.  This patch fixes it.

Fixes: 2a02759ef5f8 ("bpf: Add support for BTF pointers to interpreter")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191107014640.384083-1-kafai@fb.com

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 97e37d8..c1fde03 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1569,7 +1569,7 @@ out:
 #undef LDST
 #define LDX_PROBE(SIZEOP, SIZE)                                                        \
        LDX_PROBE_MEM_##SIZEOP:                                                 \
-               bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) SRC);    \
+               bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off));      \
                CONT;
        LDX_PROBE(B,  1)
        LDX_PROBE(H,  2)