[RFC PATCH bpf-next v2 1/6] 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/linux/syscalls.h       |  3 ++-
 include/uapi/linux/bpf.h       |  7 +++++++
 kernel/bpf/syscall.c           | 19 +++++++++++++++----
 tools/include/uapi/linux/bpf.h |  7 +++++++
 4 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 77f45e5d44139..94408575dc49b 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -933,7 +933,8 @@ asmlinkage long sys_seccomp(unsigned int op, unsigned int flags,
 asmlinkage long sys_getrandom(char __user *buf, size_t count,
 			      unsigned int flags);
 asmlinkage long sys_memfd_create(const char __user *uname_ptr, unsigned int flags);
-asmlinkage long sys_bpf(int cmd, union bpf_attr __user *attr, unsigned int size);
+asmlinkage long sys_bpf(int cmd, union bpf_attr __user *attr, unsigned int size,
+			struct bpf_common_attr __user *attr_common, unsigned int size_common);
 asmlinkage long sys_execveat(int dfd, const char __user *filename,
 			const char __user *const __user *argv,
 			const char __user *const __user *envp, int flags);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 233de8677382e..5014baccf065f 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 3f178a0f8eb12..d49f822ceea12 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5987,8 +5987,10 @@ 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;
 
@@ -6002,6 +6004,14 @@ 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;
@@ -6134,9 +6144,10 @@ 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,
@@ -6167,7 +6178,7 @@ 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 233de8677382e..5014baccf065f 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