[RFC PATCH bpf-next 1/5] bpf: Extend bpf syscall with common attributes support

[Leon Hwang <leon.hwang@linux.dev>]

This patch extends the 'bpf()' syscall to support a set of common
attributes shared across all BPF commands:

1. 'log_buf': User-provided buffer for storing logs
2. 'log_size': Size of the log buffer
3. 'log_level': Log verbosity level

These common attributes are passed as the 4th argument to the 'bpf()'
syscall, with the 5th argument specifying the size of this structure.

To indicate the use of these common attributes from userspace, a new flag
'BPF_COMMON_ATTRS' ('1 << 16') is introduced. This flag is OR-ed into the
'cmd' field of the syscall.

When 'cmd & BPF_COMMON_ATTRS' is set, the kernel will copy the common
attributes from userspace into kernel space for use.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/uapi/linux/bpf.h       |  7 +++++++
 kernel/bpf/syscall.c           | 19 +++++++++++++++----
 tools/include/uapi/linux/bpf.h |  7 +++++++
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 233de8677382..5014baccf065 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1474,6 +1474,13 @@ struct bpf_stack_build_id {
 	};
 };
 
+struct bpf_common_attr {
+	__u64 log_buf;
+	__u32 log_size;
+	__u32 log_level;
+};
+
+#define BPF_COMMON_ATTRS (1 << 16)
 #define BPF_OBJ_NAME_LEN 16U
 
 enum {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e63039817af3..ca7ce8474812 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5980,8 +5980,10 @@ static int prog_stream_read(union bpf_attr *attr)
 	return ret;
 }
 
-static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
+static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
+		     bpfptr_t uattr_common, unsigned int size_common)
 {
+	struct bpf_common_attr common_attrs;
 	union bpf_attr attr;
 	int err;
 
@@ -5995,6 +5997,14 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
 	if (copy_from_bpfptr(&attr, uattr, size) != 0)
 		return -EFAULT;
 
+	memset(&common_attrs, 0, sizeof(common_attrs));
+	if (cmd & BPF_COMMON_ATTRS) {
+		cmd &= ~BPF_COMMON_ATTRS;
+		size_common = min_t(u32, size_common, sizeof(common_attrs));
+		if (uattr_common.user && copy_from_bpfptr(&common_attrs, uattr_common, size_common))
+			return -EFAULT;
+	}
+
 	err = security_bpf(cmd, &attr, size, uattr.is_kernel);
 	if (err < 0)
 		return err;
@@ -6127,9 +6137,10 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
 	return err;
 }
 
-SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
+SYSCALL_DEFINE5(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size,
+		struct bpf_common_attr __user *, uattr_common, unsigned int, size_common)
 {
-	return __sys_bpf(cmd, USER_BPFPTR(uattr), size);
+	return __sys_bpf(cmd, USER_BPFPTR(uattr), size, USER_BPFPTR(uattr_common), size_common);
 }
 
 static bool syscall_prog_is_valid_access(int off, int size,
@@ -6160,7 +6171,7 @@ BPF_CALL_3(bpf_sys_bpf, int, cmd, union bpf_attr *, attr, u32, attr_size)
 	default:
 		return -EINVAL;
 	}
-	return __sys_bpf(cmd, KERNEL_BPFPTR(attr), attr_size);
+	return __sys_bpf(cmd, KERNEL_BPFPTR(attr), attr_size, KERNEL_BPFPTR(NULL), 0);
 }
 
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 233de8677382..5014baccf065 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1474,6 +1474,13 @@ struct bpf_stack_build_id {
 	};
 };
 
+struct bpf_common_attr {
+	__u64 log_buf;
+	__u32 log_size;
+	__u32 log_level;
+};
+
+#define BPF_COMMON_ATTRS (1 << 16)
 #define BPF_OBJ_NAME_LEN 16U
 
 enum {
-- 
2.50.1