From: Eduard Zingerman <eddyz87@xxxxxxxxx>
Changes for scalar ID tracking of spilled unbound scalars lead to
certain verification performance regression. This commit mitigates the
regression by exploiting the following properties maintained by
check_stack_read_fixed_off():
- a mix of STACK_MISC, STACK_ZERO and STACK_INVALID marks is read as
unbounded scalar register;
- spi with all slots marked STACK_ZERO is read as scalar register with
value zero.
This commit modifies stacksafe() to consider situations above
equivalent.
Veristat results after this patch show significant gains:
$ ./veristat -e file,prog,states -f '!states_pct<10' -f '!states_b<10' -C not-opt after
File Program States (A) States (B) States (DIFF)
---------------- -------- ---------- ---------- ----------------
pyperf180.bpf.o on_event 10456 8422 -2034 (-19.45%)
pyperf600.bpf.o on_event 37319 22519 -14800 (-39.66%)
strobemeta.bpf.o on_event 13435 4703 -8732 (-64.99%)
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
kernel/bpf/verifier.c | 83 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 83 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b6e252539e52..a020d4d83524 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1168,6 +1168,12 @@ static void mark_stack_slot_misc(struct bpf_verifier_env *env, u8 *stype)
*stype = STACK_MISC;
}
+static bool is_spilled_scalar_reg64(const struct bpf_stack_state *stack)
+{
+ return stack->slot_type[0] == STACK_SPILL &&
+ stack->spilled_ptr.type == SCALAR_VALUE;
+}
+
static void scrub_spilled_slot(u8 *stype)
{
if (*stype != STACK_INVALID)
@@ -16449,11 +16455,45 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
}
}
+static bool is_stack_zero64(struct bpf_stack_state *stack)
+{
+ u32 i;
+
+ for (i = 0; i < ARRAY_SIZE(stack->slot_type); ++i)
+ if (stack->slot_type[i] != STACK_ZERO)
+ return false;
+ return true;
+}
+
+static bool is_stack_unbound_slot64(struct bpf_verifier_env *env,
+ struct bpf_stack_state *stack)
+{
+ u32 i;
+
+ for (i = 0; i < ARRAY_SIZE(stack->slot_type); ++i)
+ if (stack->slot_type[i] != STACK_ZERO &&
+ stack->slot_type[i] != STACK_MISC &&
+ (!env->allow_uninit_stack || stack->slot_type[i] != STACK_INVALID))
+ return false;
+ return true;
+}
+
+static bool is_spilled_unbound_scalar_reg64(struct bpf_stack_state *stack)
+{
+ return is_spilled_scalar_reg64(stack) && __is_scalar_unbounded(&stack->spilled_ptr);
+}
+
static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
struct bpf_func_state *cur, struct bpf_idmap *idmap, bool exact)
{
+ struct bpf_reg_state unbound_reg = {};
+ struct bpf_reg_state zero_reg = {};
int i, spi;
+ __mark_reg_unknown(env, &unbound_reg);
+ __mark_reg_const_zero(env, &zero_reg);
+ zero_reg.precise = true;
+
/* walk slots of the explored stack and ignore any additional
* slots in the current stack, since explored(safe) state
* didn't use them
@@ -16474,6 +16514,49 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
continue;
}
+ /* load of stack value with all MISC and ZERO slots produces unbounded
+ * scalar value, call regsafe to ensure scalar ids are compared.
+ */
+ if (is_spilled_unbound_scalar_reg64(&old->stack[spi]) &&
+ is_stack_unbound_slot64(env, &cur->stack[spi])) {
+ i += BPF_REG_SIZE - 1;
+ if (!regsafe(env, &old->stack[spi].spilled_ptr, &unbound_reg,
+ idmap, exact))
+ return false;
+ continue;
+ }
+
+ if (is_stack_unbound_slot64(env, &old->stack[spi]) &&
+ is_spilled_unbound_scalar_reg64(&cur->stack[spi])) {
+ i += BPF_REG_SIZE - 1;
+ if (!regsafe(env, &unbound_reg, &cur->stack[spi].spilled_ptr,
+ idmap, exact))
+ return false;
+ continue;
+ }
+
+ /* load of stack value with all ZERO slots produces scalar value 0,
+ * call regsafe to ensure scalar ids are compared and precision
+ * flags are taken into account.
+ */
+ if (is_spilled_scalar_reg64(&old->stack[spi]) &&
+ is_stack_zero64(&cur->stack[spi])) {
+ if (!regsafe(env, &old->stack[spi].spilled_ptr, &zero_reg,
+ idmap, exact))
+ return false;
+ i += BPF_REG_SIZE - 1;
+ continue;
+ }
+
+ if (is_stack_zero64(&old->stack[spi]) &&
+ is_spilled_scalar_reg64(&cur->stack[spi])) {
+ if (!regsafe(env, &zero_reg, &cur->stack[spi].spilled_ptr,
+ idmap, exact))
+ return false;
+ i += BPF_REG_SIZE - 1;
+ continue;
+ }
+
if (old->stack[spi].slot_type[i % BPF_REG_SIZE] == STACK_INVALID)
continue;
--
2.42.1
