This is a note to let you know that I've just added the patch titled
bpf: fix branch pruning logic
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: bpf-fix-branch-pruning-logic.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Fri Dec 22 16:57:35 CET 2017
From: Daniel Borkmann daniel@iogearbox.net Date: Fri, 22 Dec 2017 16:29:03 +0100 Subject: bpf: fix branch pruning logic To: gregkh@linuxfoundation.org Cc: ast@kernel.org, daniel@iogearbox.net, jannh@google.com, stable@vger.kernel.org, Alexei Starovoitov ast@fb.com Message-ID: 20171222152905.3455-3-daniel@iogearbox.net
From: Daniel Borkmann daniel@iogearbox.net
From: Alexei Starovoitov ast@fb.com
[ Upstream commit c131187db2d3fa2f8bf32fdf4e9a4ef805168467 ]
when the verifier detects that register contains a runtime constant and it's compared with another constant it will prune exploration of the branch that is guaranteed not to be taken at runtime. This is all correct, but malicious program may be constructed in such a way that it always has a constant comparison and the other branch is never taken under any conditions. In this case such path through the program will not be explored by the verifier. It won't be taken at run-time either, but since all instructions are JITed the malicious program may cause JITs to complain about using reserved fields, etc. To fix the issue we have to track the instructions explored by the verifier and sanitize instructions that are dead at run time with NOPs. We cannot reject such dead code, since llvm generates it for valid C code, since it doesn't do as much data flow analysis as the verifier does.
Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)") Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/bpf_verifier.h | 1 + kernel/bpf/verifier.c | 27 +++++++++++++++++++++++++++ 2 files changed, 28 insertions(+)
--- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -68,6 +68,7 @@ struct bpf_verifier_state_list {
struct bpf_insn_aux_data { enum bpf_reg_type ptr_type; /* pointer type for load/store insns */ + bool seen; /* this insn was processed by the verifier */ };
#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */ --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2862,6 +2862,7 @@ static int do_check(struct bpf_verifier_ if (err) return err;
+ env->insn_aux_data[insn_idx].seen = true; if (class == BPF_ALU || class == BPF_ALU64) { err = check_alu_op(env, insn); if (err) @@ -3059,6 +3060,7 @@ process_bpf_exit: return err;
insn_idx++; + env->insn_aux_data[insn_idx].seen = true; } else { verbose("invalid BPF_LD mode\n"); return -EINVAL; @@ -3218,6 +3220,7 @@ static int adjust_insn_aux_data(struct b u32 off, u32 cnt) { struct bpf_insn_aux_data *new_data, *old_data = env->insn_aux_data; + int i;
if (cnt == 1) return 0; @@ -3227,6 +3230,8 @@ static int adjust_insn_aux_data(struct b memcpy(new_data, old_data, sizeof(struct bpf_insn_aux_data) * off); memcpy(new_data + off + cnt - 1, old_data + off, sizeof(struct bpf_insn_aux_data) * (prog_len - off - cnt + 1)); + for (i = off; i < off + cnt - 1; i++) + new_data[i].seen = true; env->insn_aux_data = new_data; vfree(old_data); return 0; @@ -3245,6 +3250,25 @@ static struct bpf_prog *bpf_patch_insn_d return new_prog; }
+/* The verifier does more data flow analysis than llvm and will not explore + * branches that are dead at run time. Malicious programs can have dead code + * too. Therefore replace all dead at-run-time code with nops. + */ +static void sanitize_dead_code(struct bpf_verifier_env *env) +{ + struct bpf_insn_aux_data *aux_data = env->insn_aux_data; + struct bpf_insn nop = BPF_MOV64_REG(BPF_REG_0, BPF_REG_0); + struct bpf_insn *insn = env->prog->insnsi; + const int insn_cnt = env->prog->len; + int i; + + for (i = 0; i < insn_cnt; i++) { + if (aux_data[i].seen) + continue; + memcpy(insn + i, &nop, sizeof(nop)); + } +} + /* convert load instructions that access fields of 'struct __sk_buff' * into sequence of instructions that access fields of 'struct sk_buff' */ @@ -3407,6 +3431,9 @@ skip_full_check: free_states(env);
if (ret == 0) + sanitize_dead_code(env); + + if (ret == 0) /* program is valid, convert *(u32*)(ctx + off) accesses */ ret = convert_ctx_accesses(env);
Patches currently in stable-queue which might be from daniel@iogearbox.net are
queue-4.9/bpf-fix-branch-pruning-logic.patch queue-4.9/bpf-adjust-insn_aux_data-when-patching-insns.patch queue-4.9/bpf-fix-incorrect-sign-extension-in-check_alu_op.patch queue-4.9/bpf-reject-out-of-bounds-stack-pointer-calculation.patch