Patch "bpf: fix bpf_tail_call() x64 JIT" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

bpf: fix bpf_tail_call() x64 JIT

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     bpf-fix-bpf_tail_call-x64-jit.patch

and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexei Starovoitov <[email protected]>
Date: Tue, 3 Oct 2017 15:37:20 -0700
Subject: bpf: fix bpf_tail_call() x64 JIT

From: Alexei Starovoitov <[email protected]>

[ Upstream commit 90caccdd8cc0215705f18b92771b449b01e2474a ]

- bpf prog_array just like all other types of bpf array accepts 32-bit index. Clarify that in the comment.
- fix x64 JIT of bpf_tail_call which was incorrectly loading 8 instead of 4 bytes
- tighten corresponding check in the interpreter to stay consistent

The JIT bug can be triggered after introduction of BPF_F_NUMA_NODE flag in commit 96eabe7a40aa in 4.14. Before that the map_flags would stay zero and though JIT code is wrong it will check bounds correctly.
Hence two fixes tags. All other JITs don't have this problem.

---
 arch/x86/net/bpf_jit_comp.c |    4 ++--
 include/uapi/linux/bpf.h    |    2 +-
 kernel/bpf/core.c           |    2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

@@ -282,9 +282,9 @@ static void emit_bpf_tail_call(u8 **ppro
 	/* if (index >= array->map.max_entries)
 	 *   goto out;
 	 */
-	EMIT4(0x48, 0x8B, 0x46,                   /* mov rax, qword ptr [rsi + 16] */
+	EMIT2(0x89, 0xD2);                        /* mov edx, edx */
+	EMIT3(0x39, 0x56,                         /* cmp dword ptr [rsi + 16], edx */
 	      offsetof(struct bpf_array, map.max_entries));
-	EMIT3(0x48, 0x39, 0xD0);                  /* cmp rax, rdx */
 #define OFFSET1 47 /* number of bytes to jump */
 	EMIT2(X86_JBE, OFFSET1);                  /* jbe out */
 	label1 = cnt;

@@ -294,7 +294,7 @@ union bpf_attr {
  *     jump into another BPF program
  *     @ctx: context pointer passed to next program
  *     @prog_array_map: pointer to map which type is BPF_MAP_TYPE_PROG_ARRAY
- *     @index: index inside array that selects specific program to run
+ *     @index: 32-bit index inside array that selects specific program to run
  *     Return: 0 on success or negative error
  *
  * int bpf_clone_redirect(skb, ifindex, flags)

@@ -1010,7 +1010,7 @@ select_insn:
 		struct bpf_map *map = (struct bpf_map *) (unsigned long) BPF_R2;
 		struct bpf_array *array = container_of(map, struct bpf_array, map);
 		struct bpf_prog *prog;
-		u64 index = BPF_R3;
+		u32 index = BPF_R3;
 
 		if (unlikely(index >= array->map.max_entries))
 			goto out;

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/bpf-fix-bpf_tail_call-x64-jit.patch