Re: [PATCH bpf-next v5 4/9] bpf: Add syscall common attributes support for prog_load
From: Andrii Nakryiko <hidden>
Date: 2026-01-16 00:54:35
Also in:
bpf, linux-kselftest, lkml
On Mon, Jan 12, 2026 at 6:59 AM Leon Hwang [off-list ref] wrote:
The log buffer of common attributes would be confusing with the one in 'union bpf_attr' for BPF_PROG_LOAD. In order to clarify the usage of these two log buffers, they both can be used for logging if: * They are same, including 'log_buf', 'log_level' and 'log_size'. * One of them is missing, then another one will be used for logging. If they both have 'log_buf' but they are not same totally, return -EUSERS.
why use this special error code that we don't seem to use in BPF subsystem at all? What's wrong with -EINVAL. This shouldn't be an easy mistake to do, tbh.
quoted hunk ↗ jump to hunk
Signed-off-by: Leon Hwang <redacted> --- include/linux/bpf_verifier.h | 4 +++- kernel/bpf/log.c | 29 ++++++++++++++++++++++++++--- kernel/bpf/syscall.c | 9 ++++++--- 3 files changed, 35 insertions(+), 7 deletions(-)diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 4c9632c40059..da2d37ca60e7 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h@@ -637,9 +637,11 @@ struct bpf_log_attr { u32 log_level; struct bpf_attrs *attrs; u32 offsetof_log_true_size; + struct bpf_attrs *attrs_common; }; -int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs); +int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs, + struct bpf_attrs *attrs_common); int bpf_log_attr_finalize(struct bpf_log_attr *log_attr, struct bpf_verifier_log *log); #define BPF_MAX_SUBPROGS 256diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c index 457b724c4176..eba60a13e244 100644 --- a/kernel/bpf/log.c +++ b/kernel/bpf/log.c@@ -865,23 +865,41 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st } static int bpf_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs, u64 log_buf, - u32 log_size, u32 log_level, int offsetof_log_true_size) + u32 log_size, u32 log_level, int offsetof_log_true_size, + struct bpf_attrs *attrs_common) { + const struct bpf_common_attr *common_attr = attrs_common ? attrs_common->attr : NULL; +
There is something to be said about naming choices here :) it's easy to get lost in attrs_common being actually bpf_attrs, which contains attr field, which is actually of bpf_common_attr type... It's a bit disorienting. :)
memset(log_attr, 0, sizeof(*log_attr));
log_attr->log_buf = log_buf;
log_attr->log_size = log_size;
log_attr->log_level = log_level;
log_attr->attrs = attrs;
log_attr->offsetof_log_true_size = offsetof_log_true_size;
+ log_attr->attrs_common = attrs_common;
+
+ if (log_buf && common_attr && common_attr->log_buf &&
+ (log_buf != common_attr->log_buf ||
+ log_size != common_attr->log_size ||
+ log_level != common_attr->log_level))
+ return -EUSERS;
+
+ if (!log_buf && common_attr && common_attr->log_buf) {
+ log_attr->log_buf = common_attr->log_buf;
+ log_attr->log_size = common_attr->log_size;
+ log_attr->log_level = common_attr->log_level;
+ }
+
return 0;
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