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authorYonghong Song <yhs@fb.com>2020-10-08 18:12:38 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2020-10-09 22:03:06 +0200
commit5689d49b71ad25409e41c6052dd9549fbeaf9bde (patch)
treee1d97dec229a6d4f921069149e4a008aa15366f3
parent75748837b7e56919679e02163f45d5818c644d03 (diff)
bpf: Track spill/fill of bounded scalars.
Under register pressure the llvm may spill registers with bounds into the stack. The verifier has to track them through spill/fill otherwise many kinds of bound errors will be seen. The spill/fill of induction variables was already happening. This patch extends this logic from tracking spill/fill of a constant into any bounded register. There is no need to track spill/fill of unbounded, since no new information will be retrieved from the stack during register fill. Though extra stack difference could cause state pruning to be less effective, no adverse affects were seen from this patch on selftests and on cilium programs. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20201009011240.48506-3-alexei.starovoitov@gmail.com
-rw-r--r--kernel/bpf/verifier.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ba96f7e9bbc0..f3e36eade3d4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2227,6 +2227,20 @@ static bool register_is_const(struct bpf_reg_state *reg)
return reg->type == SCALAR_VALUE && tnum_is_const(reg->var_off);
}
+static bool __is_scalar_unbounded(struct bpf_reg_state *reg)
+{
+ return tnum_is_unknown(reg->var_off) &&
+ reg->smin_value == S64_MIN && reg->smax_value == S64_MAX &&
+ reg->umin_value == 0 && reg->umax_value == U64_MAX &&
+ reg->s32_min_value == S32_MIN && reg->s32_max_value == S32_MAX &&
+ reg->u32_min_value == 0 && reg->u32_max_value == U32_MAX;
+}
+
+static bool register_is_bounded(struct bpf_reg_state *reg)
+{
+ return reg->type == SCALAR_VALUE && !__is_scalar_unbounded(reg);
+}
+
static bool __is_pointer_value(bool allow_ptr_leaks,
const struct bpf_reg_state *reg)
{
@@ -2278,7 +2292,7 @@ static int check_stack_write(struct bpf_verifier_env *env,
if (value_regno >= 0)
reg = &cur->regs[value_regno];
- if (reg && size == BPF_REG_SIZE && register_is_const(reg) &&
+ if (reg && size == BPF_REG_SIZE && register_is_bounded(reg) &&
!register_is_null(reg) && env->bpf_capable) {
if (dst_reg != BPF_REG_FP) {
/* The backtracking logic can only recognize explicit