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bpf: extend is_branch_taken to registers

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commit fb8d251ee2 upstream

This patch extends is_branch_taken() logic from JMP+K instructions
to JMP+X instructions.
Conditional branches are often done when src and dst registers
contain known scalars. In such case the verifier can follow
the branch that is going to be taken when program executes.
That speeds up the verification and is essential feature to support
bounded loops.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
[OP: drop is_jmp32 parameter from is_branch_taken() calls and
     adjust context]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexei Starovoitov
2021-05-28 13:37:56 +03:00
committed by Greg Kroah-Hartman
parent c905bfe767
commit e0b86677fb
1 changed files with 18 additions and 14 deletions
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32
kernel/bpf/verifier.c
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@@ -4127,8 +4127,9 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
struct bpf_verifier_state *this_branch = env->cur_state;
struct bpf_verifier_state *other_branch;
struct bpf_reg_state *regs = this_branch->frame[this_branch->curframe]->regs;
struct bpf_reg_state *dst_reg, *other_branch_regs;
struct bpf_reg_state *dst_reg, *other_branch_regs, *src_reg = NULL;
u8 opcode = BPF_OP(insn->code);
int pred = -1;
int err;
if (opcode > BPF_JSLE) {
@@ -4152,6 +4153,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
insn->src_reg);
return -EACCES;
}
src_reg = &regs[insn->src_reg];
} else {
if (insn->src_reg != BPF_REG_0) {
verbose(env, "BPF_JMP uses reserved fields\n");
@@ -4166,19 +4168,21 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
dst_reg = &regs[insn->dst_reg];
if (BPF_SRC(insn->code) == BPF_K) {
int pred = is_branch_taken(dst_reg, insn->imm, opcode);
if (pred == 1) {
/* only follow the goto, ignore fall-through */
*insn_idx += insn->off;
return 0;
} else if (pred == 0) {
/* only follow fall-through branch, since
* that's where the program will go
*/
return 0;
}
if (BPF_SRC(insn->code) == BPF_K)
pred = is_branch_taken(dst_reg, insn->imm, opcode);
else if (src_reg->type == SCALAR_VALUE &&
tnum_is_const(src_reg->var_off))
pred = is_branch_taken(dst_reg, src_reg->var_off.value,
opcode);
if (pred == 1) {
/* only follow the goto, ignore fall-through */
*insn_idx += insn->off;
return 0;
} else if (pred == 0) {
/* only follow fall-through branch, since
* that's where the program will go
*/
return 0;
}
other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx,