[PATCH bpf-next v9 1/9] bpf: Extend BPF syscall with common attributes support

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

Extend 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.
4. 'log_true_size': The size of log reported by kernel.

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       |  8 ++++++++
 kernel/bpf/syscall.c           | 25 +++++++++++++++++++++----
 tools/include/uapi/linux/bpf.h |  8 ++++++++
 4 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index cf84d98964b2..729659202d77 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -937,7 +937,8 @@ 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 c8d400b7680a..b2126c9641ec 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -994,6 +994,7 @@ enum bpf_cmd {
 	BPF_PROG_STREAM_READ_BY_FD,
 	BPF_PROG_ASSOC_STRUCT_OPS,
 	__MAX_BPF_CMD,
+	BPF_COMMON_ATTRS = 1 << 16, /* Indicate carrying syscall common attrs. */
 };
 
 enum bpf_map_type {
@@ -1500,6 +1501,13 @@ struct bpf_stack_build_id {
 	};
 };
 
+struct bpf_common_attr {
+	__u64 log_buf;
+	__u32 log_size;
+	__u32 log_level;
+	__u32 log_true_size;
+};
+
 #define BPF_OBJ_NAME_LEN 16U
 
 enum {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5f59dd47a5b1..a58b16735e86 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -6176,8 +6176,10 @@ static int prog_assoc_struct_ops(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 attr_common;
 	union bpf_attr attr;
 	int err;
 
@@ -6191,6 +6193,20 @@ 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(&attr_common, 0, sizeof(attr_common));
+	if (cmd & BPF_COMMON_ATTRS) {
+		err = bpf_check_uarg_tail_zero(uattr_common, sizeof(attr_common), size_common);
+		if (err)
+			return err;
+
+		cmd &= ~BPF_COMMON_ATTRS;
+		size_common = min_t(u32, size_common, sizeof(attr_common));
+		if (copy_from_bpfptr(&attr_common, uattr_common, size_common) != 0)
+			return -EFAULT;
+	} else {
+		size_common = 0;
+	}
+
 	err = security_bpf(cmd, &attr, size, uattr.is_kernel);
 	if (err < 0)
 		return err;
@@ -6326,9 +6342,10 @@ 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,
@@ -6359,7 +6376,7 @@ 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 5e38b4887de6..c4934c2370fd 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -994,6 +994,7 @@ enum bpf_cmd {
 	BPF_PROG_STREAM_READ_BY_FD,
 	BPF_PROG_ASSOC_STRUCT_OPS,
 	__MAX_BPF_CMD,
+	BPF_COMMON_ATTRS = 1 << 16, /* Indicate carrying syscall common attrs. */
 };
 
 enum bpf_map_type {
@@ -1500,6 +1501,13 @@ struct bpf_stack_build_id {
 	};
 };
 
+struct bpf_common_attr {
+	__u64 log_buf;
+	__u32 log_size;
+	__u32 log_level;
+	__u32 log_true_size;
+};
+
 #define BPF_OBJ_NAME_LEN 16U
 
 enum {
-- 
2.52.0