On Wed, Feb 4, 2026 at 7:42 PM Leon Hwang <[email protected]> wrote:
>
>
>
> On 5/2/26 03:48, Andrii Nakryiko wrote:
> > On Mon, Feb 2, 2026 at 6:42 AM Leon Hwang <[email protected]> wrote:
> >>
> >> BPF_PROG_LOAD can now provide log parameters through both union bpf_attr
> >> and struct bpf_common_attr. Define clear conflict and precedence rules:
> >>
> >> - if both are provided and log_buf/log_size/log_level match, use them;
> >> - if only one side provides a log buffer, use that one;
> >> - if both provide log buffers but differ, return -EINVAL.
> >>
> >> Signed-off-by: Leon Hwang <[email protected]>
> >> ---
> >> include/linux/bpf_verifier.h | 3 ++-
> >> kernel/bpf/log.c | 24 ++++++++++++++++++++++--
> >> kernel/bpf/syscall.c | 3 ++-
> >> 3 files changed, 26 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> >> index c805b85b6f7a..0d106fddbbc5 100644
> >> --- a/include/linux/bpf_verifier.h
> >> +++ b/include/linux/bpf_verifier.h
> >> @@ -638,7 +638,8 @@ struct bpf_log_attr {
> >> };
> >>
> >> int bpf_prog_load_log_attr_init(struct bpf_log_attr *attr_log, union
> >> bpf_attr *attr,
> >> - bpfptr_t uattr, u32 size);
> >> + bpfptr_t uattr, u32 size, struct
> >> bpf_common_attr *attr_common,
> >> + bpfptr_t uattr_common, u32 size_common);
> >> int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct
> >> bpf_verifier_log *log);
> >>
> >> #define BPF_MAX_SUBPROGS 256
> >> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> >> index ff579fcba36f..345005ba98dd 100644
> >> --- a/kernel/bpf/log.c
> >> +++ b/kernel/bpf/log.c
> >> @@ -873,10 +873,30 @@ static void bpf_log_attr_init(struct bpf_log_attr
> >> *attr_log, int offsetof_true_s
> >> attr_log->uattr = uattr;
> >> }
> >>
> >> +static bool bpf_log_attrs_diff(struct bpf_common_attr *common, u64
> >> log_buf, u32 log_size,
> >> + u32 log_level)
> >> +{
> >> + return log_buf && common->log_buf && (log_buf != common->log_buf ||
> >> + log_size != common->log_size
> >> ||
> >> + log_level !=
> >> common->log_level);
> >
> > let's validate (unless we do this somewhere else) that if log_buf is
> > set, then log_size and log_level (? not sure, maybe zero is fine) are
> > set, or all three are not set. Same for common->log* fields...
> >
>
> Ack.
>
> Will validate 'log_buf && log_size && log_level' first.
>
> >
> >> +}
> >> +
> >> int bpf_prog_load_log_attr_init(struct bpf_log_attr *attr_log, union
> >> bpf_attr *attr,
> >> - bpfptr_t uattr, u32 size)
> >> + bpfptr_t uattr, u32 size, struct
> >> bpf_common_attr *attr_common,
> >> + bpfptr_t uattr_common, u32 size_common)
> >> {
> >> - bpf_log_attr_init(attr_log, offsetof(union bpf_attr,
> >> log_true_size), uattr, size);
> >> + if (bpf_log_attrs_diff(attr_common, attr->log_buf, attr->log_size,
> >> attr->log_level))
> >> + return -EINVAL;
> >> +
> >> + if (!attr->log_buf && attr_common->log_buf) {
> >> + attr->log_buf = attr_common->log_buf;
> >> + attr->log_size = attr_common->log_size;
> >> + attr->log_level = attr_common->log_level;
> >
> > why are we setting this? Do we still have code that can access
> > attr->log_buf even though we pass attr_log everywhere? If yes, should
> > we still have that "split brain" code?
> >
>
> 'attr->log_buf' is accessed only in bpf_check().
bpf_check should be changed then, see below
>
> > If we don't have this assignment, then I think we don't need to have
> > bpf_prog_load-specific and btf_load-specific log_attr_init() helpers.
> > They can be unified into generic log_attr_init, where for
> > bpf_prog_load you'll pass offsetof(log_true_size) +
> > attr->log_{buf,size,level}, and for btf_load you'll pass different
> > offset of and btf-specific attr->btf_log*
> >
> > This helper will just be making decision whether to use common_attr's
> > log fields or passed directly command-specific ones.
> >
> > Or what am I missing?
> >
>
> If the log attributes differ, where should the effective
> log_* values be stored?
>
> Should they live in struct bpf_common_attr, or should we extend
> struct bpf_log_attr to carry them?
>
> Note that in v8, Alexei suggested struct bpf_log_attr only needs
> u32 offsetof_true_size;
> bpfptr_t uattr;
>
> so I’d like to clarify the intended direction here. Once that’s clear, a
> single generic log_attr_init() should be sufficient to handle this.
>
The intended direction is to have log buf/size/level in one place
(after attr and common_attr validations), so we keep internal logic
simple. Let's put all of that and log_true_size **pointer** (we don't
have to much with offsetof, just calculate user addr for
log_true_size, which just might be NULL) into bpf_log_attrs and teach
all code to look and work *only* with that struct, ignoring anything
log related from attr.
> Thanks,
> Leon
>
> >
> >> + bpf_log_attr_init(attr_log, offsetof(struct
> >> bpf_common_attr, log_true_size),
> >> + uattr_common, size_common);
> >> + } else {
> >> + bpf_log_attr_init(attr_log, offsetof(union bpf_attr,
> >> log_true_size), uattr, size);
> >> + }
> >> return 0;
> >> }
> >>
> >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> >> index e81199361241..7125ea445c6c 100644
> >> --- a/kernel/bpf/syscall.c
> >> +++ b/kernel/bpf/syscall.c
> >> @@ -6232,7 +6232,8 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t
> >> uattr, unsigned int size,
> >> err = map_freeze(&attr);
> >> break;
> >> case BPF_PROG_LOAD:
> >> - err = bpf_prog_load_log_attr_init(&attr_log, &attr, uattr,
> >> size);
> >> + err = bpf_prog_load_log_attr_init(&attr_log, &attr, uattr,
> >> size, &attr_common,
> >> + uattr_common,
> >> size_common);
> >> err = err ?: bpf_prog_load(&attr, uattr, &attr_log);
> >> break;
> >> case BPF_OBJ_PIN:
> >> --
> >> 2.52.0
> >>
>
