From: Jiri Olsa Date: Thu, 11 Jun 2026 11:42:26 +0000 (+0200) Subject: bpf: Add support to specify uprobe_multi target via file descriptor X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=26330a9226417c9a3395db9fdb403f7d7371e6b7;p=thirdparty%2Flinux.git bpf: Add support to specify uprobe_multi target via file descriptor Allow uprobe_multi link to identify the target binary by an already opened file descriptor. Adding new BPF_F_UPROBE_MULTI_PATH_FD flag and the path_fd field for the attr.link_create.uprobe_multi struct. When the flag is set, we resolve the target from path_fd, without the flag, we keep the existing string path behavior. I don't see a use case for supporting O_PATH file descriptors, because we need to read the binary first to get probes offsets, so I'm using the CLASS(fd, f), which fails for O_PATH fds. Assisted-by: Codex:GPT-5.4 Signed-off-by: Jiri Olsa Link: https://lore.kernel.org/r/20260611114230.950379-4-jolsa@kernel.org Signed-off-by: Alexei Starovoitov --- diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 11dd610fa5fa..89b36de5fdbb 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1327,7 +1327,11 @@ enum { * BPF_TRACE_UPROBE_MULTI attach type to create return probe. */ enum { - BPF_F_UPROBE_MULTI_RETURN = (1U << 0) + /* Get return uprobe. */ + BPF_F_UPROBE_MULTI_RETURN = (1U << 0), + + /* Get path from provided path_fd. */ + BPF_F_UPROBE_MULTI_PATH_FD = (1U << 1), }; /* link_create.netfilter.flags used in LINK_CREATE command for @@ -1864,6 +1868,7 @@ union bpf_attr { __u32 cnt; __u32 flags; __u32 pid; + __u32 path_fd; } uprobe_multi; struct { union { diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 7ed949f70f82..b44106c8ea75 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3480,7 +3480,7 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp) seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_KPROBE_MULTI_RETURN ? "kretprobe_multi" : "kprobe_multi"); else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI) - seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_UPROBE_MULTI_RETURN ? + seq_printf(m, "link_type:\t%s\n", link->flags & BPF_F_UPROBE_MULTI_RETURN ? "uretprobe_multi" : "uprobe_multi"); else seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]); @@ -5840,7 +5840,7 @@ err_put: return err; } -#define BPF_LINK_CREATE_LAST_FIELD link_create.uprobe_multi.pid +#define BPF_LINK_CREATE_LAST_FIELD link_create.uprobe_multi.path_fd static int link_create(union bpf_attr *attr, bpfptr_t uattr) { struct bpf_prog *prog; diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index f8990bc6b64c..82f8feea6931 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -23,6 +23,7 @@ #include #include #include +#include #include @@ -3214,6 +3215,38 @@ static u64 bpf_uprobe_multi_cookie(struct bpf_run_ctx *ctx) return run_ctx->uprobe->cookie; } +static int bpf_uprobe_multi_get_path(const union bpf_attr *attr, struct path *path) +{ + void __user *upath = u64_to_user_ptr(attr->link_create.uprobe_multi.path); + u32 path_fd = attr->link_create.uprobe_multi.path_fd; + u32 flags = attr->link_create.uprobe_multi.flags; + + if (flags & BPF_F_UPROBE_MULTI_PATH_FD) { + /* + * When BPF_F_UPROBE_MULTI_PATH_FD is set, the executable is + * identified by path_fd, upath must be NULL. + */ + if (upath) + return -EINVAL; + + CLASS(fd, f)(path_fd); + if (fd_empty(f)) + return -EBADF; + *path = fd_file(f)->f_path; + path_get(path); + return 0; + } + + /* + * When BPF_F_UPROBE_MULTI_PATH_FD is not set, the path is resolved + * relative to the cwd (AT_FDCWD) or absolute using the upath string. + */ + if (!upath || path_fd) + return -EINVAL; + + return user_path_at(AT_FDCWD, upath, LOOKUP_FOLLOW, path); +} + int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) { struct bpf_uprobe_multi_link *link = NULL; @@ -3223,7 +3256,6 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr struct task_struct *task = NULL; unsigned long __user *uoffsets; u64 __user *ucookies; - void __user *upath; unsigned long size; u32 flags, cnt, i; struct path path; @@ -3241,19 +3273,18 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr return -EINVAL; flags = attr->link_create.uprobe_multi.flags; - if (flags & ~BPF_F_UPROBE_MULTI_RETURN) + if (flags & ~(BPF_F_UPROBE_MULTI_RETURN | BPF_F_UPROBE_MULTI_PATH_FD)) return -EINVAL; /* - * path, offsets and cnt are mandatory, + * offsets and cnt are mandatory, * ref_ctr_offsets and cookies are optional */ - upath = u64_to_user_ptr(attr->link_create.uprobe_multi.path); uoffsets = u64_to_user_ptr(attr->link_create.uprobe_multi.offsets); cnt = attr->link_create.uprobe_multi.cnt; pid = attr->link_create.uprobe_multi.pid; - if (!upath || !uoffsets || !cnt || pid < 0) + if (!uoffsets || !cnt || pid < 0) return -EINVAL; if (cnt > MAX_UPROBE_MULTI_CNT) return -E2BIG; @@ -3271,7 +3302,7 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr !access_ok(ucookies, size)) return -EFAULT; - err = user_path_at(AT_FDCWD, upath, LOOKUP_FOLLOW, &path); + err = bpf_uprobe_multi_get_path(attr, &path); if (err) return err; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 11dd610fa5fa..89b36de5fdbb 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -1327,7 +1327,11 @@ enum { * BPF_TRACE_UPROBE_MULTI attach type to create return probe. */ enum { - BPF_F_UPROBE_MULTI_RETURN = (1U << 0) + /* Get return uprobe. */ + BPF_F_UPROBE_MULTI_RETURN = (1U << 0), + + /* Get path from provided path_fd. */ + BPF_F_UPROBE_MULTI_PATH_FD = (1U << 1), }; /* link_create.netfilter.flags used in LINK_CREATE command for @@ -1864,6 +1868,7 @@ union bpf_attr { __u32 cnt; __u32 flags; __u32 pid; + __u32 path_fd; } uprobe_multi; struct { union {