From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit f655badf2a8fc028433d9583bf86a6b473721f09 ]
Fix propagate_precision() logic to perform propagation of all necessary registers and stack slots across all active frames *in one batch step*.
Doing this for each register/slot in each individual frame is wasteful, but the main problem is that backtracking of instruction in any frame except the deepest one just doesn't work. This is due to backtracking logic relying on jump history, and available jump history always starts (or ends, depending how you view it) in current frame. So, if prog A (frame #0) called subprog B (frame #1) and we need to propagate precision of, say, register R6 (callee-saved) within frame #0, we actually don't even know where jump history that corresponds to prog A even starts. We'd need to skip subprog part of jump history first to be able to do this.
Luckily, with struct backtrack_state and __mark_chain_precision() handling bitmasks tracking/propagation across all active frames at the same time (added in previous patch), propagate_precision() can be both fixed and sped up by setting all the necessary bits across all frames and then performing one __mark_chain_precision() pass. This makes it unnecessary to skip subprog parts of jump history.
We also improve logging along the way, to clearly specify which registers' and slots' precision markings are propagated within which frame. Each frame will have dedicated line and all registers and stack slots from that frame will be reported in format similar to precision backtrack regs/stack logging. E.g.:
frame 1: propagating r1,r2,r3,fp-8,fp-16 frame 0: propagating r3,r9,fp-120
Fixes: 529409ea92d5 ("bpf: propagate precision across all frames, not just the last one") Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/r/20230505043317.3629845-7-andrii@kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 65 +++++++++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 30 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index bc4cf078e6277..fb0aee90ccfaa 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3684,8 +3684,7 @@ static void mark_all_scalars_imprecise(struct bpf_verifier_env *env, struct bpf_ * mark_all_scalars_imprecise() to hopefully get more permissive and generic * finalized states which help in short circuiting more future states. */ -static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int regno, - int spi) +static int __mark_chain_precision(struct bpf_verifier_env *env, int regno) { struct backtrack_state *bt = &env->bt; struct bpf_verifier_state *st = env->cur_state; @@ -3700,13 +3699,13 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r return 0;
/* set frame number from which we are starting to backtrack */ - bt_init(bt, frame); + bt_init(bt, env->cur_state->curframe);
/* Do sanity checks against current state of register and/or stack * slot, but don't set precise flag in current state, as precision * tracking in the current state is unnecessary. */ - func = st->frame[frame]; + func = st->frame[bt->frame]; if (regno >= 0) { reg = &func->regs[regno]; if (reg->type != SCALAR_VALUE) { @@ -3716,13 +3715,6 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r bt_set_reg(bt, regno); }
- while (spi >= 0) { - if (!is_spilled_scalar_reg(&func->stack[spi])) - break; - bt_set_slot(bt, spi); - break; - } - if (bt_empty(bt)) return 0;
@@ -3872,17 +3864,15 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r
int mark_chain_precision(struct bpf_verifier_env *env, int regno) { - return __mark_chain_precision(env, env->cur_state->curframe, regno, -1); -} - -static int mark_chain_precision_frame(struct bpf_verifier_env *env, int frame, int regno) -{ - return __mark_chain_precision(env, frame, regno, -1); + return __mark_chain_precision(env, regno); }
-static int mark_chain_precision_stack_frame(struct bpf_verifier_env *env, int frame, int spi) +/* mark_chain_precision_batch() assumes that env->bt is set in the caller to + * desired reg and stack masks across all relevant frames + */ +static int mark_chain_precision_batch(struct bpf_verifier_env *env) { - return __mark_chain_precision(env, frame, -1, spi); + return __mark_chain_precision(env, -1); }
static bool is_spillable_regtype(enum bpf_reg_type type) @@ -15298,20 +15288,25 @@ static int propagate_precision(struct bpf_verifier_env *env, struct bpf_reg_state *state_reg; struct bpf_func_state *state; int i, err = 0, fr; + bool first;
for (fr = old->curframe; fr >= 0; fr--) { state = old->frame[fr]; state_reg = state->regs; + first = true; for (i = 0; i < BPF_REG_FP; i++, state_reg++) { if (state_reg->type != SCALAR_VALUE || !state_reg->precise || !(state_reg->live & REG_LIVE_READ)) continue; - if (env->log.level & BPF_LOG_LEVEL2) - verbose(env, "frame %d: propagating r%d\n", fr, i); - err = mark_chain_precision_frame(env, fr, i); - if (err < 0) - return err; + if (env->log.level & BPF_LOG_LEVEL2) { + if (first) + verbose(env, "frame %d: propagating r%d", fr, i); + else + verbose(env, ",r%d", i); + } + bt_set_frame_reg(&env->bt, fr, i); + first = false; }
for (i = 0; i < state->allocated_stack / BPF_REG_SIZE; i++) { @@ -15322,14 +15317,24 @@ static int propagate_precision(struct bpf_verifier_env *env, !state_reg->precise || !(state_reg->live & REG_LIVE_READ)) continue; - if (env->log.level & BPF_LOG_LEVEL2) - verbose(env, "frame %d: propagating fp%d\n", - fr, (-i - 1) * BPF_REG_SIZE); - err = mark_chain_precision_stack_frame(env, fr, i); - if (err < 0) - return err; + if (env->log.level & BPF_LOG_LEVEL2) { + if (first) + verbose(env, "frame %d: propagating fp%d", + fr, (-i - 1) * BPF_REG_SIZE); + else + verbose(env, ",fp%d", (-i - 1) * BPF_REG_SIZE); + } + bt_set_frame_slot(&env->bt, fr, i); + first = false; } + if (!first) + verbose(env, "\n"); } + + err = mark_chain_precision_batch(env); + if (err < 0) + return err; + return 0; }