diff mbox series

bpf: increase frame warning limit in verifier when using KASAN or KCSAN

Message ID 20240613021942.46743-1-flyingpeng@tencent.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series bpf: increase frame warning limit in verifier when using KASAN or KCSAN | expand

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Commit Message

Hao Peng June 13, 2024, 2:19 a.m. UTC 
From: Peng Hao <flyingpeng@tencent.com>

When building kernel with clang, which will typically
have sanitizers enabled, there is a warning about a large stack frame.

kernel/bpf/verifier.c:21163:5: error: stack frame size (2392) exceeds
limit (2048) in 'bpf_check' [-Werror,-Wframe-larger-than]
int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
__u32 uattr_size)
    ^
632/2392 (26.42%) spills, 1760/2392 (73.58%) variables
so increase the limit for configurations that have KASAN or KCSAN enabled for not
breaking the majority of builds.

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
---
 kernel/bpf/Makefile | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Alexei Starovoitov June 13, 2024, 3:02 a.m. UTC | #1 
On Wed, Jun 12, 2024 at 7:19 PM <flyingpenghao@gmail.com> wrote:
>
> From: Peng Hao <flyingpeng@tencent.com>
>
> When building kernel with clang, which will typically
> have sanitizers enabled, there is a warning about a large stack frame.
>
> kernel/bpf/verifier.c:21163:5: error: stack frame size (2392) exceeds
> limit (2048) in 'bpf_check' [-Werror,-Wframe-larger-than]
> int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
> __u32 uattr_size)
>     ^
> 632/2392 (26.42%) spills, 1760/2392 (73.58%) variables
> so increase the limit for configurations that have KASAN or KCSAN enabled for not
> breaking the majority of builds.
>
> Signed-off-by: Peng Hao <flyingpeng@tencent.com>
> ---
>  kernel/bpf/Makefile | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index e497011261b8..07ed1e81aa62 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -6,6 +6,12 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
>  endif
>  CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
>
> +ifneq ($(CONFIG_FRAME_WARN),0)
> +ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
> +CFLAGS_verifier.o = -Wframe-larger-than=2392

that's very compiler specific.
version +-1 will have different results.
Please investigate what is causing the large stack size instead.
pw-bot: cr
Hao Peng July 10, 2024, 3:19 a.m. UTC | #2 
On Thu, Jun 13, 2024 at 11:02 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Jun 12, 2024 at 7:19 PM <flyingpenghao@gmail.com> wrote:
> >
> > From: Peng Hao <flyingpeng@tencent.com>
> >
> > When building kernel with clang, which will typically
> > have sanitizers enabled, there is a warning about a large stack frame.
> >
> > kernel/bpf/verifier.c:21163:5: error: stack frame size (2392) exceeds
> > limit (2048) in 'bpf_check' [-Werror,-Wframe-larger-than]
> > int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
> > __u32 uattr_size)
> >     ^
> > 632/2392 (26.42%) spills, 1760/2392 (73.58%) variables
> > so increase the limit for configurations that have KASAN or KCSAN enabled for not
> > breaking the majority of builds.
> >
> > Signed-off-by: Peng Hao <flyingpeng@tencent.com>
> > ---
> >  kernel/bpf/Makefile | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> > index e497011261b8..07ed1e81aa62 100644
> > --- a/kernel/bpf/Makefile
> > +++ b/kernel/bpf/Makefile
> > @@ -6,6 +6,12 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
> >  endif
> >  CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
> >
> > +ifneq ($(CONFIG_FRAME_WARN),0)
> > +ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
> > +CFLAGS_verifier.o = -Wframe-larger-than=2392
>
> that's very compiler specific.
> version +-1 will have different results.
> Please investigate what is causing the large stack size instead.
> pw-bot: cr
This increase in stack frame size only occurs when KASAN or KCSAN is
configured. KASAN or
KCSAN will cause the stack frame size to increase, and it will insert
additional code and data
structures to detect memory errors during compilation. These
additional checks will increase
the stack space requirements of the function.
Thanks.
Alexei Starovoitov July 10, 2024, 6:29 p.m. UTC | #3 
On Tue, Jul 9, 2024 at 8:19 PM Hao Peng <flyingpenghao@gmail.com> wrote:
>
> On Thu, Jun 13, 2024 at 11:02 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Jun 12, 2024 at 7:19 PM <flyingpenghao@gmail.com> wrote:
> > >
> > > From: Peng Hao <flyingpeng@tencent.com>
> > >
> > > When building kernel with clang, which will typically
> > > have sanitizers enabled, there is a warning about a large stack frame.
> > >
> > > kernel/bpf/verifier.c:21163:5: error: stack frame size (2392) exceeds
> > > limit (2048) in 'bpf_check' [-Werror,-Wframe-larger-than]
> > > int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
> > > __u32 uattr_size)
> > >     ^
> > > 632/2392 (26.42%) spills, 1760/2392 (73.58%) variables
> > > so increase the limit for configurations that have KASAN or KCSAN enabled for not
> > > breaking the majority of builds.
> > >
> > > Signed-off-by: Peng Hao <flyingpeng@tencent.com>
> > > ---
> > >  kernel/bpf/Makefile | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> > > index e497011261b8..07ed1e81aa62 100644
> > > --- a/kernel/bpf/Makefile
> > > +++ b/kernel/bpf/Makefile
> > > @@ -6,6 +6,12 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
> > >  endif
> > >  CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
> > >
> > > +ifneq ($(CONFIG_FRAME_WARN),0)
> > > +ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
> > > +CFLAGS_verifier.o = -Wframe-larger-than=2392
> >
> > that's very compiler specific.
> > version +-1 will have different results.
> > Please investigate what is causing the large stack size instead.
> > pw-bot: cr
> This increase in stack frame size only occurs when KASAN or KCSAN is
> configured. KASAN or
> KCSAN will cause the stack frame size to increase, and it will insert
> additional code and data
> structures to detect memory errors during compilation. These
> additional checks will increase
> the stack space requirements of the function.

This generic statement about kasan is not helpful.
Figure out which exact variables and what functions are causing this
kasan behavior.
diff mbox series

Patch

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index e497011261b8..07ed1e81aa62 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -6,6 +6,12 @@  cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
 endif
 CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
 
+ifneq ($(CONFIG_FRAME_WARN),0)
+ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
+CFLAGS_verifier.o = -Wframe-larger-than=2392
+endif
+endif
+
 obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o log.o token.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o