[bpf-next,v4] bpf: Fix test verif_scale_strobemeta_subprogs failure due to llvm19

Commit Message

Yonghong Song Feb. 14, 2024, 11:29 p.m. UTC

With latest llvm19, I hit the following selftest failures with

  $ ./test_progs -j
  libbpf: prog 'on_event': BPF program load failed: Permission denied
  libbpf: prog 'on_event': -- BEGIN PROG LOAD LOG --
  combined stack size of 4 calls is 544. Too large
  verification time 1344153 usec
  stack depth 24+440+0+32
  processed 51008 insns (limit 1000000) max_states_per_insn 19 total_states 1467 peak_states 303 mark_read 146
  -- END PROG LOAD LOG --
  libbpf: prog 'on_event': failed to load: -13
  libbpf: failed to load object 'strobemeta_subprogs.bpf.o'
  scale_test:FAIL:expect_success unexpected error: -13 (errno 13)
  #498     verif_scale_strobemeta_subprogs:FAIL

The verifier complains too big of the combined stack size (544 bytes) which
exceeds the maximum stack limit 512. This is a regression from llvm19 ([1]).

In the above error log, the original stack depth is 24+440+0+32.
To satisfy interpreter's need, in verifier the stack depth is adjusted to
32+448+32+32=544 which exceeds 512, hence the error. The same adjusted
stack size is also used for jit case.

But the jitted codes could use smaller stack size.

  $ egrep -r stack_depth | grep round_up
  arm64/net/bpf_jit_comp.c:       ctx->stack_size = round_up(prog->aux->stack_depth, 16);
  loongarch/net/bpf_jit.c:        bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
  powerpc/net/bpf_jit_comp.c:     cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
  riscv/net/bpf_jit_comp32.c:             round_up(ctx->prog->aux->stack_depth, STACK_ALIGN);
  riscv/net/bpf_jit_comp64.c:     bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
  s390/net/bpf_jit_comp.c:        u32 stack_depth = round_up(fp->aux->stack_depth, 8);
  sparc/net/bpf_jit_comp_64.c:            stack_needed += round_up(stack_depth, 16);
  x86/net/bpf_jit_comp.c:         EMIT3_off32(0x48, 0x81, 0xEC, round_up(stack_depth, 8));
  x86/net/bpf_jit_comp.c: int tcc_off = -4 - round_up(stack_depth, 8);
  x86/net/bpf_jit_comp.c:                     round_up(stack_depth, 8));
  x86/net/bpf_jit_comp.c: int tcc_off = -4 - round_up(stack_depth, 8);
  x86/net/bpf_jit_comp.c:         EMIT3_off32(0x48, 0x81, 0xC4, round_up(stack_depth, 8));

In the above, STACK_ALIGN in riscv/net/bpf_jit_comp32.c is defined as 16.
So stack is aligned in either 8 or 16, x86/s390 having 8-byte stack alignment and
the rest having 16-byte alignment.

This patch calculates total stack depth based on 16-byte alignment if jit is requested.
For the above failing case, the new stack size will be 32+448+0+32=512 and no verification
failure. llvm19 regression will be discussed separately in llvm upstream.

The verifier change caused three test failures as these tests compared messages
with stack size. More specifically,
  - test_global_funcs/global_func1: fail with interpreter mode and success with jit mode.
    Adjusted stack sizes so both jit and interpreter modes will fail.
  - async_stack_depth/{pseudo_call_check, async_call_root_check}: since jit and interpreter
    will calculate different stack sizes, the failure msg is adjusted to omit those
    specific stack size numbers.

  [1] https://lore.kernel.org/bpf/[e-mail]/

Suggested-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Yonghong Song <[e-mail]>
---
 kernel/bpf/verifier.c                          | 18 +++++++++++++-----
 .../selftests/bpf/progs/async_stack_depth.c    |  4 ++--
 .../selftests/bpf/progs/test_global_func1.c    |  8 ++++++--
 3 files changed, 21 insertions(+), 9 deletions(-)

Changelogs:
  v3 -> v4:
    - make a change in test_global_funcs/global_func1 so both interpreter and
      jit modes failed the test.
  v2 -> v3:
    - fix async_stack_depth test failure if jit is turned off
  v1 -> v2:
    - fix some selftest failures

Comments

[e-mail] Feb. 15, 2024, 10 p.m. UTC | #1

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Wed, 14 Feb 2024 15:29:51 -0800 you wrote:
> With latest llvm19, I hit the following selftest failures with
> 
>   $ ./test_progs -j
>   libbpf: prog 'on_event': BPF program load failed: Permission denied
>   libbpf: prog 'on_event': -- BEGIN PROG LOAD LOG --
>   combined stack size of 4 calls is 544. Too large
>   verification time 1344153 usec
>   stack depth 24+440+0+32
>   processed 51008 insns (limit 1000000) max_states_per_insn 19 total_states 1467 peak_states 303 mark_read 146
>   -- END PROG LOAD LOG --
>   libbpf: prog 'on_event': failed to load: -13
>   libbpf: failed to load object 'strobemeta_subprogs.bpf.o'
>   scale_test:FAIL:expect_success unexpected error: -13 (errno 13)
>   #498     verif_scale_strobemeta_subprogs:FAIL
> 
> [...]

Here is the summary with links:
  - [bpf-next,v4] bpf: Fix test verif_scale_strobemeta_subprogs failure due to llvm19
    https://git.kernel.org/bpf/bpf-next/c/682158ab532a

You are awesome, thank you!

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index aa192dc735a9..011d54a1dc53 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5812,6 +5812,17 @@  static int check_ptr_alignment(struct bpf_verifier_env *env,
 					   strict);
 }
 
+static int round_up_stack_depth(struct bpf_verifier_env *env, int stack_depth)
+{
+	if (env->prog->jit_requested)
+		return round_up(stack_depth, 16);
+
+	/* round up to 32-bytes, since this is granularity
+	 * of interpreter stack size
+	 */
+	return round_up(max_t(u32, stack_depth, 1), 32);
+}
+
 /* starting from main bpf function walk all instructions of the function
  * and recursively walk all callees that given function can call.
  * Ignore jump and exit insns.
@@ -5855,10 +5866,7 @@  static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx)
 			depth);
 		return -EACCES;
 	}
-	/* round up to 32-bytes, since this is granularity
-	 * of interpreter stack size
-	 */
-	depth += round_up(max_t(u32, subprog[idx].stack_depth, 1), 32);
+	depth += round_up_stack_depth(env, subprog[idx].stack_depth);
 	if (depth > MAX_BPF_STACK) {
 		verbose(env, "combined stack size of %d calls is %d. Too large\n",
 			frame + 1, depth);
@@ -5952,7 +5960,7 @@  static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx)
 	 */
 	if (frame == 0)
 		return 0;
-	depth -= round_up(max_t(u32, subprog[idx].stack_depth, 1), 32);
+	depth -= round_up_stack_depth(env, subprog[idx].stack_depth);
 	frame--;
 	i = ret_insn[frame];
 	idx = ret_prog[frame];
diff --git a/tools/testing/selftests/bpf/progs/async_stack_depth.c b/tools/testing/selftests/bpf/progs/async_stack_depth.c
index 3517c0e01206..36734683acbd 100644
--- a/tools/testing/selftests/bpf/progs/async_stack_depth.c
+++ b/tools/testing/selftests/bpf/progs/async_stack_depth.c
@@ -30,7 +30,7 @@  static int bad_timer_cb(void *map, int *key, struct bpf_timer *timer)
 }
 
 SEC("tc")
-__failure __msg("combined stack size of 2 calls is 576. Too large")
+__failure __msg("combined stack size of 2 calls is")
 int pseudo_call_check(struct __sk_buff *ctx)
 {
 	struct hmap_elem *elem;
@@ -45,7 +45,7 @@  int pseudo_call_check(struct __sk_buff *ctx)
 }
 
 SEC("tc")
-__failure __msg("combined stack size of 2 calls is 608. Too large")
+__failure __msg("combined stack size of 2 calls is")
 int async_call_root_check(struct __sk_buff *ctx)
 {
 	struct hmap_elem *elem;
diff --git a/tools/testing/selftests/bpf/progs/test_global_func1.c b/tools/testing/selftests/bpf/progs/test_global_func1.c
index 17a9f59bf5f3..fc69ff18880d 100644
--- a/tools/testing/selftests/bpf/progs/test_global_func1.c
+++ b/tools/testing/selftests/bpf/progs/test_global_func1.c
@@ -5,7 +5,7 @@ 
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
 
-#define MAX_STACK (512 - 3 * 32 + 8)
+#define MAX_STACK 260
 
 static __attribute__ ((noinline))
 int f0(int var, struct __sk_buff *skb)
@@ -30,6 +30,10 @@  int f3(int, struct __sk_buff *skb, int);
 __attribute__ ((noinline))
 int f2(int val, struct __sk_buff *skb)
 {
+	volatile char buf[MAX_STACK] = {};
+
+	__sink(buf[MAX_STACK - 1]);
+
 	return f1(skb) + f3(val, skb, 1);
 }
 
@@ -44,7 +48,7 @@  int f3(int val, struct __sk_buff *skb, int var)
 }
 
 SEC("tc")
-__failure __msg("combined stack size of 4 calls is 544")
+__failure __msg("combined stack size of 3 calls is")
 int global_func1(struct __sk_buff *skb)
 {
 	return f0(1, skb) + f1(skb) + f2(2, skb) + f3(3, skb, 4);