From: Sandipan Das <sandipan@linux.vnet.ibm.com>
Date: Thu, 24 May 2018 12:26:45 +0530
Subject: bpf: support 64-bit offsets for bpf function calls
Patch-mainline: v4.18-rc1
Git-commit: 2162fed49fa86cb3b5c296565837e674c53cc7ae
References: bsc#1109837

The imm field of a bpf instruction is a signed 32-bit integer.
For JITed bpf-to-bpf function calls, it holds the offset of the
start address of the callee's JITed image from __bpf_call_base.

For some architectures, such as powerpc64, this offset may be
as large as 64 bits and cannot be accomodated in the imm field
without truncation.

We resolve this by:

[1] Additionally using the auxiliary data of each function to
    keep a list of start addresses of the JITed images for all
    functions determined by the verifier.

[2] Retaining the subprog id inside the off field of the call
    instructions and using it to index into the list mentioned
    above and lookup the callee's address.

To make sure that the existing JIT compilers continue to work
without requiring changes, we keep the imm field as it is.

Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/verifier.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5425,11 +5425,24 @@ static int jit_subprogs(struct bpf_verif
 			    insn->src_reg != BPF_PSEUDO_CALL)
 				continue;
 			subprog = insn->off;
-			insn->off = 0;
 			insn->imm = (u64 (*)(u64, u64, u64, u64, u64))
 				func[subprog]->bpf_func -
 				__bpf_call_base;
 		}
+
+		/* we use the aux data to keep a list of the start addresses
+		 * of the JITed images for each function in the program
+		 *
+		 * for some architectures, such as powerpc64, the imm field
+		 * might not be large enough to hold the offset of the start
+		 * address of the callee's JITed image from __bpf_call_base
+		 *
+		 * in such cases, we can lookup the start address of a callee
+		 * by using its subprog id, available from the off field of
+		 * the call instruction, as an index for this list
+		 */
+		func[i]->aux->func = func;
+		func[i]->aux->func_cnt = env->subprog_cnt;
 	}
 	for (i = 0; i < env->subprog_cnt; i++) {
 		old_bpf_func = func[i]->bpf_func;