[PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[Emil Tsalapatis]

The veristat tool verifies that BPF objects along with their
maps pass verification for a given kernel version. To do so,
veristat loads the objects and maps into the kernel in order
to pass them through the verifier.

Currently, veristat sizes the maps according to the max_entries
field provided by the program author. Depending on the map type
this field may be irrelevant to the verification process. However,
loading a large map can fail because of -ENOMEM errors.

This is a problem when the map is supposed to run on large machines,
but veristat tests it machines with significantly less RAM (e.g.,
CI). In that case veristat fails even if the program verifies.

Expand veristat to resize maps whose max_entries are not relevant
to verification. Set the max_entries value as low as possible to
avoid -ENOMEM errors.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>

CHANGELOG
=========

v2->v3

- Do not resize HASH_OF_MAPS because it can be declaratively populated
from BPF at compile time (Sashiko)

v1->v2

- Removed unnecessary ARENA, LPM_TRIE, and RHASH handling (Sashiko)
---
 tools/testing/selftests/bpf/veristat.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
index a7db6f04f7e1..c9c257784ee3 100644
--- a/tools/testing/selftests/bpf/veristat.c
+++ b/tools/testing/selftests/bpf/veristat.c
@@ -1248,6 +1248,29 @@ static void fixup_obj_maps(struct bpf_object *obj)
 
 		/* fix up map size, if necessary */
 		switch (bpf_map__type(map)) {
+		/*
+		 * if the verifier doesn't use max_entries
+		 * then set to 1 to avoid -ENOMEM
+		 */
+		case BPF_MAP_TYPE_HASH:
+		case BPF_MAP_TYPE_PERCPU_HASH:
+		case BPF_MAP_TYPE_LRU_HASH:
+		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
+		case BPF_MAP_TYPE_SOCKHASH:
+		case BPF_MAP_TYPE_DEVMAP_HASH:
+		case BPF_MAP_TYPE_QUEUE:
+		case BPF_MAP_TYPE_STACK:
+		case BPF_MAP_TYPE_BLOOM_FILTER:
+		case BPF_MAP_TYPE_STACK_TRACE:
+			bpf_map__set_max_entries(map, 1);
+			break;
+
+		/* ringbufs must be page-aligned */
+		case BPF_MAP_TYPE_RINGBUF:
+		case BPF_MAP_TYPE_USER_RINGBUF:
+			bpf_map__set_max_entries(map, sysconf(_SC_PAGESIZE));
+			break;
+
 		case BPF_MAP_TYPE_SK_STORAGE:
 		case BPF_MAP_TYPE_TASK_STORAGE:
 		case BPF_MAP_TYPE_INODE_STORAGE:
-- 
2.54.0

Re: [PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[Andrii Nakryiko]

On Wed, Jul 8, 2026 at 12:32 PM Emil Tsalapatis <emil@etsalapatis.com> wrote:
>
> The veristat tool verifies that BPF objects along with their
> maps pass verification for a given kernel version. To do so,
> veristat loads the objects and maps into the kernel in order
> to pass them through the verifier.
>
> Currently, veristat sizes the maps according to the max_entries
> field provided by the program author. Depending on the map type
> this field may be irrelevant to the verification process. However,
> loading a large map can fail because of -ENOMEM errors.
>
> This is a problem when the map is supposed to run on large machines,
> but veristat tests it machines with significantly less RAM (e.g.,
> CI). In that case veristat fails even if the program verifies.
>
> Expand veristat to resize maps whose max_entries are not relevant
> to verification. Set the max_entries value as low as possible to
> avoid -ENOMEM errors.
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
>
> CHANGELOG
> =========
>

for individual patches we normally don't commit changelog, so next
time put it under `---` below so it will be stripped out during
applying (I cleaned this up manually)

> v2->v3
>
> - Do not resize HASH_OF_MAPS because it can be declaratively populated
> from BPF at compile time (Sashiko)
>
> v1->v2
>
> - Removed unnecessary ARENA, LPM_TRIE, and RHASH handling (Sashiko)
> ---
>  tools/testing/selftests/bpf/veristat.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
> index a7db6f04f7e1..c9c257784ee3 100644
> --- a/tools/testing/selftests/bpf/veristat.c
> +++ b/tools/testing/selftests/bpf/veristat.c
> @@ -1248,6 +1248,29 @@ static void fixup_obj_maps(struct bpf_object *obj)
>
>                 /* fix up map size, if necessary */
>                 switch (bpf_map__type(map)) {
> +               /*
> +                * if the verifier doesn't use max_entries
> +                * then set to 1 to avoid -ENOMEM
> +                */
> +               case BPF_MAP_TYPE_HASH:


I'm wondering if we should add ARRAY here as that one is actually with
high likelihood will be large, though there are some corner cases
where size might matter (e.g., existing code omits error checking
knowing that verifier will prove it can never fail; resizing to 1
might pessimize such check, probably, if index is larger than 1). Can
you actually try the latter scenario with some small program, I'm
curious how the verifier will behave?

anyways, applied to bpf-next, thanks!

> +               case BPF_MAP_TYPE_PERCPU_HASH:
> +               case BPF_MAP_TYPE_LRU_HASH:
> +               case BPF_MAP_TYPE_LRU_PERCPU_HASH:
> +               case BPF_MAP_TYPE_SOCKHASH:
> +               case BPF_MAP_TYPE_DEVMAP_HASH:
> +               case BPF_MAP_TYPE_QUEUE:
> +               case BPF_MAP_TYPE_STACK:
> +               case BPF_MAP_TYPE_BLOOM_FILTER:
> +               case BPF_MAP_TYPE_STACK_TRACE:
> +                       bpf_map__set_max_entries(map, 1);
> +                       break;
> +
> +               /* ringbufs must be page-aligned */
> +               case BPF_MAP_TYPE_RINGBUF:
> +               case BPF_MAP_TYPE_USER_RINGBUF:
> +                       bpf_map__set_max_entries(map, sysconf(_SC_PAGESIZE));
> +                       break;
> +
>                 case BPF_MAP_TYPE_SK_STORAGE:
>                 case BPF_MAP_TYPE_TASK_STORAGE:
>                 case BPF_MAP_TYPE_INODE_STORAGE:
> --
> 2.54.0
>

Re: [PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[Eduard Zingerman]

On Fri, 2026-07-10 at 14:44 -0700, Andrii Nakryiko wrote:

[...]

> > @@ -1248,6 +1248,29 @@ static void fixup_obj_maps(struct bpf_object *obj)
> >
> >                 /* fix up map size, if necessary */
> >                 switch (bpf_map__type(map)) {
> > +               /*
> > +                * if the verifier doesn't use max_entries
> > +                * then set to 1 to avoid -ENOMEM
> > +                */
> > +               case BPF_MAP_TYPE_HASH:
>
>
> I'm wondering if we should add ARRAY here as that one is actually with
> high likelihood will be large, though there are some corner cases
> where size might matter (e.g., existing code omits error checking
> knowing that verifier will prove it can never fail; resizing to 1
> might pessimize such check, probably, if index is larger than 1). Can
> you actually try the latter scenario with some small program, I'm
> curious how the verifier will behave?

For array maps there are several complications: first is the constant
maps handling and second is null check elision. The latter is somewhat
nasty, see check_helper_call():

         case RET_PTR_TO_MAP_VALUE:
                 ...
                 if (func_id == BPF_FUNC_map_lookup_elem &&
                     can_elide_value_nullness(meta.map.ptr) && <-------- true for array maps
                     meta.const_map_key >= 0 &&
                     meta.const_map_key < meta.map.ptr->max_entries) <-- checks max_entries
                         ret_flag &= ~PTR_MAYBE_NULL;

[...]

Re: [PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[Andrii Nakryiko]

On Fri, Jul 10, 2026 at 2:50 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>
> On Fri, 2026-07-10 at 14:44 -0700, Andrii Nakryiko wrote:
>
> [...]
>
> > > @@ -1248,6 +1248,29 @@ static void fixup_obj_maps(struct bpf_object *obj)
> > >
> > >                 /* fix up map size, if necessary */
> > >                 switch (bpf_map__type(map)) {
> > > +               /*
> > > +                * if the verifier doesn't use max_entries
> > > +                * then set to 1 to avoid -ENOMEM
> > > +                */
> > > +               case BPF_MAP_TYPE_HASH:
> >
> >
> > I'm wondering if we should add ARRAY here as that one is actually with
> > high likelihood will be large, though there are some corner cases
> > where size might matter (e.g., existing code omits error checking
> > knowing that verifier will prove it can never fail; resizing to 1
> > might pessimize such check, probably, if index is larger than 1). Can
> > you actually try the latter scenario with some small program, I'm
> > curious how the verifier will behave?
>
> For array maps there are several complications: first is the constant
> maps handling and second is null check elision. The latter is somewhat
> nasty, see check_helper_call():
>

yeah, I was thinking about that bit. Worst case, (valid) BPF code can
have, say, 8-element array and have all the keys within [0, 7] range,
by *decreasing* map to less than 8 elements we actually force NULL
check.

Anyways, ARRAY, I believe, is one of the maps that caused this
feature, so I think maybe we should still do a dirt-but-practical
approach, and just cap ARRAY size if it exceeds some modest size
(e.g., 128K, or something).

Oh well, capping non-ARRAYs is useful anyways, so let's keep it as is for now.

>          case RET_PTR_TO_MAP_VALUE:
>                  ...
>                  if (func_id == BPF_FUNC_map_lookup_elem &&
>                      can_elide_value_nullness(meta.map.ptr) && <-------- true for array maps
>                      meta.const_map_key >= 0 &&
>                      meta.const_map_key < meta.map.ptr->max_entries) <-- checks max_entries
>                          ret_flag &= ~PTR_MAYBE_NULL;
>
> [...]

Re: [PATCH bpf-next v3] selftests/bpf: veristat: Minimize map size during verification

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed,  8 Jul 2026 15:32:39 -0400 you wrote:
> The veristat tool verifies that BPF objects along with their
> maps pass verification for a given kernel version. To do so,
> veristat loads the objects and maps into the kernel in order
> to pass them through the verifier.
> 
> Currently, veristat sizes the maps according to the max_entries
> field provided by the program author. Depending on the map type
> this field may be irrelevant to the verification process. However,
> loading a large map can fail because of -ENOMEM errors.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v3] selftests/bpf: veristat: Minimize map size during verification
    https://git.kernel.org/bpf/bpf-next/c/e821c2238758

You are awesome, thank you!
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