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authorEduard Zingerman <eddyz87@gmail.com>2023-02-15 02:20:27 +0300
committerAlexei Starovoitov <ast@kernel.org>2023-02-15 22:48:47 +0300
commitecdf985d7615356b78241fdb159c091830ed0380 (patch)
tree09cc7458a92f11576b1eb4d10f10aa97bf6372dc /kernel
parent62d101d5f422cde39b269f7eb4cbbe2f1e26f9d4 (diff)
downloadlinux-ecdf985d7615356b78241fdb159c091830ed0380.tar.xz
bpf: track immediate values written to stack by BPF_ST instruction
For aligned stack writes using BPF_ST instruction track stored values in a same way BPF_STX is handled, e.g. make sure that the following commands produce similar verifier knowledge: fp[-8] = 42; r1 = 42; fp[-8] = r1; This covers two cases: - non-null values written to stack are stored as spill of fake registers; - null values written to stack are stored as STACK_ZERO marks. Previously both cases above used STACK_MISC marks instead. Some verifier test cases relied on the old logic to obtain STACK_MISC marks for some stack values. These test cases are updated in the same commit to avoid failures during bisect. Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Link: https://lore.kernel.org/r/20230214232030.1502829-2-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c18
1 files changed, 16 insertions, 2 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 21e08c111702..c28afae60874 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3473,6 +3473,11 @@ static void save_register_state(struct bpf_func_state *state,
scrub_spilled_slot(&state->stack[spi].slot_type[i - 1]);
}
+static bool is_bpf_st_mem(struct bpf_insn *insn)
+{
+ return BPF_CLASS(insn->code) == BPF_ST && BPF_MODE(insn->code) == BPF_MEM;
+}
+
/* check_stack_{read,write}_fixed_off functions track spill/fill of registers,
* stack boundary and alignment are checked in check_mem_access()
*/
@@ -3484,8 +3489,9 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
{
struct bpf_func_state *cur; /* state of the current function */
int i, slot = -off - 1, spi = slot / BPF_REG_SIZE, err;
- u32 dst_reg = env->prog->insnsi[insn_idx].dst_reg;
+ struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
struct bpf_reg_state *reg = NULL;
+ u32 dst_reg = insn->dst_reg;
err = grow_stack_state(state, round_up(slot + 1, BPF_REG_SIZE));
if (err)
@@ -3538,6 +3544,13 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
return err;
}
save_register_state(state, spi, reg, size);
+ } else if (!reg && !(off % BPF_REG_SIZE) && is_bpf_st_mem(insn) &&
+ insn->imm != 0 && env->bpf_capable) {
+ struct bpf_reg_state fake_reg = {};
+
+ __mark_reg_known(&fake_reg, (u32)insn->imm);
+ fake_reg.type = SCALAR_VALUE;
+ save_register_state(state, spi, &fake_reg, size);
} else if (reg && is_spillable_regtype(reg->type)) {
/* register containing pointer is being spilled into stack */
if (size != BPF_REG_SIZE) {
@@ -3572,7 +3585,8 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
state->stack[spi].spilled_ptr.live |= REG_LIVE_WRITTEN;
/* when we zero initialize stack slots mark them as such */
- if (reg && register_is_null(reg)) {
+ if ((reg && register_is_null(reg)) ||
+ (!reg && is_bpf_st_mem(insn) && insn->imm == 0)) {
/* backtracking doesn't work for STACK_ZERO yet. */
err = mark_chain_precision(env, value_regno);
if (err)