From: Alexei Starovoitov <ast@kernel.org>
Date: Thu, 13 Dec 2018 11:42:33 -0800
Subject: bpf: improve stacksafe state comparison
Patch-mainline: v5.0
Git-commit: 19e2dbb7dd978d24505e918ac54d6f7dfdc88b1d
References: bsc#1160618
"if (old->allocated_stack > cur->allocated_stack)" check is too conservative.
In some cases explored stack could have allocated more space,
but that stack space was not live.
The test case improves from 19 to 15 processed insns
and improvement on real programs is significant as well:
before after
bpf_lb-DLB_L3.o 1940 1831
bpf_lb-DLB_L4.o 3089 3029
bpf_lb-DUNKNOWN.o 1065 1064
bpf_lxc-DDROP_ALL.o 28052 26309
bpf_lxc-DUNKNOWN.o 35487 33517
bpf_netdev.o 10864 9713
bpf_overlay.o 6643 6184
bpf_lcx_jit.o 38437 37335
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Edward Cree <ecree@solarflare.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Michal Rostecki <mrostecki@suse.de>
---
kernel/bpf/verifier.c | 13 +++++++------
tools/testing/selftests/bpf/test_verifier.c | 22 ++++++++++++++++++++++
2 files changed, 29 insertions(+), 6 deletions(-)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4645,12 +4645,6 @@ static bool stacksafe(struct bpf_func_st
{
int i, spi;
- /* if explored stack has more populated slots than current stack
- * such stacks are not equivalent
- */
- if (old->allocated_stack > cur->allocated_stack)
- return false;
-
/* walk slots of the explored stack and ignore any additional
* slots in the current stack, since explored(safe) state
* didn't use them
@@ -4666,6 +4660,13 @@ static bool stacksafe(struct bpf_func_st
if (old->stack[spi].slot_type[i % BPF_REG_SIZE] == STACK_INVALID)
continue;
+
+ /* explored stack has more populated slots than current stack
+ * and these slots were used
+ */
+ if (i >= cur->allocated_stack)
+ return false;
+
/* if old state was safe with misc data in the stack
* it will be safe with zero-initialized stack.
* The opposite is not true
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -12535,6 +12535,28 @@ static struct bpf_test tests[] = {
.result = ACCEPT,
},
{
+ "allocated_stack",
+ .insns = {
+ BPF_ALU64_REG(BPF_MOV, BPF_REG_6, BPF_REG_1),
+ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_prandom_u32),
+ BPF_ALU64_REG(BPF_MOV, BPF_REG_7, BPF_REG_0),
+ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 5),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_6, -8),
+ BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_10, -8),
+ BPF_STX_MEM(BPF_B, BPF_REG_10, BPF_REG_7, -9),
+ BPF_LDX_MEM(BPF_B, BPF_REG_7, BPF_REG_10, -9),
+ BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 0),
+ BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 0),
+ BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 0),
+ BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ .result_unpriv = ACCEPT,
+ .insn_processed = 15,
+ },
+ {
"calls: cross frame pruning",
.insns = {
/* r8 = !!random();