linux-kernel - [PATCH 4.17 137/336] bpf: fix multi-function JITed dump obtained via syscall

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Message-Id: <20180801165034.371476003@linuxfoundation.org>
Date:   Wed,  1 Aug 2018 18:47:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sandipan Das <sandipan@...ux.vnet.ibm.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.17 137/336] bpf: fix multi-function JITed dump obtained via syscall

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sandipan Das <sandipan@...ux.vnet.ibm.com>

[ Upstream commit 4d56a76ead2fcd856e677cdc9445ad331a409b8c ]

Currently, for multi-function programs, we cannot get the JITed
instructions using the bpf system call's BPF_OBJ_GET_INFO_BY_FD
command. Because of this, userspace tools such as bpftool fail
to identify a multi-function program as being JITed or not.

With the JIT enabled and the test program running, this can be
verified as follows:

  # cat /proc/sys/net/core/bpf_jit_enable
  1

Before applying this patch:

  # bpftool prog list
  1: kprobe  name foo  tag b811aab41a39ad3d  gpl
          loaded_at 2018-05-16T11:43:38+0530  uid 0
          xlated 216B  not jited  memlock 65536B
  ...

  # bpftool prog dump jited id 1
  no instructions returned

After applying this patch:

  # bpftool prog list
  1: kprobe  name foo  tag b811aab41a39ad3d  gpl
          loaded_at 2018-05-16T12:13:01+0530  uid 0
          xlated 216B  jited 308B  memlock 65536B
  ...

  # bpftool prog dump jited id 1
     0:   nop
     4:   nop
     8:   mflr    r0
     c:   std     r0,16(r1)
    10:   stdu    r1,-112(r1)
    14:   std     r31,104(r1)
    18:   addi    r31,r1,48
    1c:   li      r3,10
  ...

Signed-off-by: Sandipan Das <sandipan@...ux.vnet.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/bpf/syscall.c |   37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1946,13 +1946,44 @@ static int bpf_prog_get_info_by_fd(struc
 	 * for offload.
 	 */
 	ulen = info.jited_prog_len;
-	info.jited_prog_len = prog->jited_len;
+	if (prog->aux->func_cnt) {
+		u32 i;
+
+		info.jited_prog_len = 0;
+		for (i = 0; i < prog->aux->func_cnt; i++)
+			info.jited_prog_len += prog->aux->func[i]->jited_len;
+	} else {
+		info.jited_prog_len = prog->jited_len;
+	}
+
 	if (info.jited_prog_len && ulen) {
 		if (bpf_dump_raw_ok()) {
 			uinsns = u64_to_user_ptr(info.jited_prog_insns);
 			ulen = min_t(u32, info.jited_prog_len, ulen);
-			if (copy_to_user(uinsns, prog->bpf_func, ulen))
-				return -EFAULT;
+
+			/* for multi-function programs, copy the JITed
+			 * instructions for all the functions
+			 */
+			if (prog->aux->func_cnt) {
+				u32 len, free, i;
+				u8 *img;
+
+				free = ulen;
+				for (i = 0; i < prog->aux->func_cnt; i++) {
+					len = prog->aux->func[i]->jited_len;
+					len = min_t(u32, len, free);
+					img = (u8 *) prog->aux->func[i]->bpf_func;
+					if (copy_to_user(uinsns, img, len))
+						return -EFAULT;
+					uinsns += len;
+					free -= len;
+					if (!free)
+						break;
+				}
+			} else {
+				if (copy_to_user(uinsns, prog->bpf_func, ulen))
+					return -EFAULT;
+			}
 		} else {
 			info.jited_prog_insns = 0;
 		}