lsm: cgroup attachment type support

Author: Altug Bozkurt

aya-ebpf-macros/src/lib.rs

@@ -10,6 +10,7 @@ mod fentry;
 mod fexit;
 mod kprobe;
 mod lsm;
+mod lsm_cgroup;
 mod map;
 mod perf_event;
 mod raw_tracepoint;
@@ -34,6 +35,7 @@ use fentry::FEntry;
 use fexit::FExit;
 use kprobe::{KProbe, KProbeKind};
 use lsm::Lsm;
+use lsm_cgroup::LsmCgroup;
 use map::Map;
 use perf_event::PerfEvent;
 use proc_macro::TokenStream;
@@ -326,6 +328,49 @@ pub fn lsm(attrs: TokenStream, item: TokenStream) -> TokenStream {
     .into()
 }
 
+/// Marks a function as an LSM program that can be attached to cgroups.
+/// This program will only trigger for workloads in the attached cgroups.
+/// Used to implement security policy and audit logging.
+///
+/// The hook name is the first and only argument to the macro.
+///
+/// LSM probes can be attached to the kernel's security hooks to implement mandatory
+/// access control policy and security auditing.
+///
+/// LSM probes require a kernel compiled with `CONFIG_BPF_LSM=y` and `CONFIG_DEBUG_INFO_BTF=y`.
+/// In order for the probes to fire, you also need the BPF LSM to be enabled through your
+/// kernel's boot paramters (like `lsm=lockdown,yama,bpf`).
+///
+/// # Minimum kernel version
+///
+/// The minimum kernel version required to use this feature is 6.0.
+///
+/// # Examples
+///
+/// ```no_run
+/// use aya_ebpf::{macros::lsm_cgroup, programs::LsmContext};
+///
+/// #[lsm_cgroup(hook = "file_open")]
+/// pub fn file_open(ctx: LsmContext) -> i32 {
+///     match unsafe { try_file_open(ctx) } {
+///         Ok(ret) => ret,
+///         Err(ret) => ret,
+///     }
+/// }
+///
+/// unsafe fn try_file_open(_ctx: LsmContext) -> Result<i32, i32> {
+///     Err(0)
+/// }
+/// ```
+#[proc_macro_attribute]
+pub fn lsm_cgroup(attrs: TokenStream, item: TokenStream) -> TokenStream {
+    match LsmCgroup::parse(attrs.into(), item.into()) {
+        Ok(prog) => prog.expand(),
+        Err(err) => err.into_compile_error(),
+    }
+    .into()
+}
+
 /// Marks a function as a [BTF-enabled raw tracepoint][1] eBPF program that can be attached at
 /// a pre-defined kernel trace point.
 ///

aya-ebpf-macros/src/lsm.rs

@@ -44,10 +44,10 @@ impl Lsm {
         } else {
             section_prefix.into()
         };
+        let fn_name = &sig.ident;
         // LSM probes need to return an integer corresponding to the correct
         // policy decision. Therefore we do not simply default to a return value
         // of 0 as in other program types.
-        let fn_name = &sig.ident;
         quote! {
             #[no_mangle]
             #[link_section = #section_name]

aya-ebpf-macros/src/lsm_cgroup.rs

@@ -0,0 +1,87 @@
+use std::borrow::Cow;
+
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{ItemFn, Result};
+
+use crate::args::{err_on_unknown_args, pop_string_arg};
+
+pub(crate) struct LsmCgroup {
+    item: ItemFn,
+    hook: Option<String>,
+}
+
+impl LsmCgroup {
+    pub(crate) fn parse(attrs: TokenStream, item: TokenStream) -> Result<Self> {
+        let item = syn::parse2(item)?;
+        let mut args = syn::parse2(attrs)?;
+        let hook = pop_string_arg(&mut args, "hook");
+        err_on_unknown_args(&args)?;
+
+        Ok(Self { item, hook })
+    }
+
+    pub(crate) fn expand(&self) -> TokenStream {
+        let Self { item, hook } = self;
+        let ItemFn {
+            attrs: _,
+            vis,
+            sig,
+            block: _,
+        } = item;
+        let section_prefix = "lsm_cgroup";
+        let section_name: Cow<'_, _> = if let Some(name) = hook {
+            format!("{}/{}", section_prefix, name).into()
+        } else {
+            section_prefix.into()
+        };
+        let fn_name = &sig.ident;
+        // LSM probes need to return an integer corresponding to the correct
+        // policy decision. Therefore we do not simply default to a return value
+        // of 0 as in other program types.
+        quote! {
+            #[no_mangle]
+            #[link_section = #section_name]
+            #vis fn #fn_name(ctx: *mut ::core::ffi::c_void) -> i32 {
+                return #fn_name(::aya_ebpf::programs::LsmContext::new(ctx));
+
+                #item
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use syn::parse_quote;
+
+    use super::*;
+
+    #[test]
+    fn test_lsm_cgroup() {
+        let prog = LsmCgroup::parse(
+            parse_quote! {
+                hook = "bprm_committed_creds",
+            },
+            parse_quote! {
+                fn bprm_committed_creds(ctx: &mut ::aya_ebpf::programs::LsmContext) -> i32 {
+                    0
+                }
+            },
+        )
+        .unwrap();
+        let expanded = prog.expand();
+        let expected = quote! {
+            #[no_mangle]
+            #[link_section = "lsm_cgroup/bprm_committed_creds"]
+            fn bprm_committed_creds(ctx: *mut ::core::ffi::c_void) -> i32 {
+                return bprm_committed_creds(::aya_ebpf::programs::LsmContext::new(ctx));
+
+                fn bprm_committed_creds(ctx: &mut ::aya_ebpf::programs::LsmContext) -> i32 {
+                    0
+                }
+            }
+        };
+        assert_eq!(expected.to_string(), expanded.to_string());
+    }
+}

aya-obj/src/obj.rs

@@ -275,6 +275,7 @@ pub enum ProgramSection {
     Lsm {
         sleepable: bool,
     },
+    LsmCgroup,
     BtfTracePoint,
     FEntry {
         sleepable: bool,
@@ -436,6 +437,7 @@ impl FromStr for ProgramSection {
             "raw_tp" | "raw_tracepoint" => RawTracePoint,
             "lsm" => Lsm { sleepable: false },
             "lsm.s" => Lsm { sleepable: true },
+            "lsm_cgroup" => LsmCgroup,
             "fentry" => FEntry { sleepable: false },
             "fentry.s" => FEntry { sleepable: true },
             "fexit" => FExit { sleepable: false },
@@ -2188,10 +2190,7 @@ mod tests {
         assert_matches!(
             obj.programs.get("foo"),
             Some(Program {
-                section: ProgramSection::Lsm {
-                    sleepable: false,
-                    ..
-                },
+                section: ProgramSection::Lsm { sleepable: false },
                 ..
             })
         );
@@ -2223,6 +2222,29 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_parse_section_lsm_cgroup() {
+        let mut obj = fake_obj();
+        fake_sym(&mut obj, 0, 0, "foo", FAKE_INS_LEN);
+
+        assert_matches!(
+            obj.parse_section(fake_section(
+                EbpfSectionKind::Program,
+                "lsm_cgroup/foo",
+                bytes_of(&fake_ins()),
+                None
+            )),
+            Ok(())
+        );
+        assert_matches!(
+            obj.programs.get("foo"),
+            Some(Program {
+                section: ProgramSection::LsmCgroup { .. },
+                ..
+            })
+        );
+    }
+
     #[test]
     fn test_parse_section_btf_tracepoint() {
         let mut obj = fake_obj();

aya/src/bpf.rs

@@ -30,8 +30,9 @@ use crate::{
     programs::{
         BtfTracePoint, CgroupDevice, CgroupSkb, CgroupSkbAttachType, CgroupSock, CgroupSockAddr,
         CgroupSockopt, CgroupSysctl, Extension, FEntry, FExit, Iter, KProbe, LircMode2, Lsm,
-        PerfEvent, ProbeKind, Program, ProgramData, ProgramError, RawTracePoint, SchedClassifier,
-        SkLookup, SkMsg, SkSkb, SkSkbKind, SockOps, SocketFilter, TracePoint, UProbe, Xdp,
+        LsmCgroup, PerfEvent, ProbeKind, Program, ProgramData, ProgramError, RawTracePoint,
+        SchedClassifier, SkLookup, SkMsg, SkSkb, SkSkbKind, SockOps, SocketFilter, TracePoint,
+        UProbe, Xdp,
     },
     sys::{
         bpf_load_btf, is_bpf_cookie_supported, is_bpf_global_data_supported,
@@ -412,6 +413,7 @@ impl<'a> EbpfLoader<'a> {
                                 | ProgramSection::FEntry { sleepable: _ }
                                 | ProgramSection::FExit { sleepable: _ }
                                 | ProgramSection::Lsm { sleepable: _ }
+                                | ProgramSection::LsmCgroup
                                 | ProgramSection::BtfTracePoint
                                 | ProgramSection::Iter { sleepable: _ } => {
                                     return Err(EbpfError::BtfError(err))
@@ -657,6 +659,9 @@ impl<'a> EbpfLoader<'a> {
                             }
                             Program::Lsm(Lsm { data })
                         }
+                        ProgramSection::LsmCgroup => Program::LsmCgroup(LsmCgroup {
+                            data: ProgramData::new(prog_name, obj, btf_fd, *verifier_log_level),
+                        }),
                         ProgramSection::BtfTracePoint => Program::BtfTracePoint(BtfTracePoint {
                             data: ProgramData::new(prog_name, obj, btf_fd, *verifier_log_level),
                         }),

aya/src/programs/lsm_cgroup.rs

@@ -0,0 +1,105 @@
+//! LSM probes.
+
+use std::os::fd::AsFd;
+
+use crate::{
+    generated::{bpf_attach_type::BPF_LSM_CGROUP, bpf_prog_type::BPF_PROG_TYPE_LSM},
+    obj::btf::{Btf, BtfKind},
+    programs::{define_link_wrapper, load_program, FdLink, FdLinkId, ProgramData, ProgramError},
+    sys::{bpf_link_create, BpfLinkCreateArgs, LinkTarget, SyscallError},
+};
+
+/// A program that attaches to Linux LSM hooks with per-cgroup attachment type. Used to implement security policy and
+/// audit logging.
+///
+/// LSM probes can be attached to the kernel's [security hooks][1] to implement mandatory
+/// access control policy and security auditing.
+///
+/// LSM probes require a kernel compiled with `CONFIG_BPF_LSM=y` and `CONFIG_DEBUG_INFO_BTF=y`.
+/// In order for the probes to fire, you also need the BPF LSM to be enabled through your
+/// kernel's boot paramters (like `lsm=lockdown,yama,bpf`).
+///
+/// # Minimum kernel version
+///
+/// The minimum kernel version required to use this feature is 6.0.
+///
+/// # Examples
+///
+/// ```no_run
+/// # #[derive(thiserror::Error, Debug)]
+/// # enum LsmError {
+/// #     #[error(transparent)]
+/// #     BtfError(#[from] aya::BtfError),
+/// #     #[error(transparent)]
+/// #     Program(#[from] aya::programs::ProgramError),
+/// #     #[error(transparent)]
+/// #     Ebpf(#[from] aya::EbpfError),
+/// # }
+/// # let mut bpf = Ebpf::load_file("ebpf_programs.o")?;
+/// use aya::{Ebpf, programs::LsmCgroup, BtfError, Btf};
+/// use std::fs::File;
+///
+/// let btf = Btf::from_sys_fs()?;
+/// let file = File::open("/sys/fs/cgroup/unified").unwrap();
+/// let program: &mut LsmCgroup = bpf.program_mut("lsm_prog").unwrap().try_into()?;
+/// program.load("security_bprm_exec", &btf)?;
+/// program.attach(file)?;
+/// # Ok::<(), LsmError>(())
+/// ```
+///
+/// [1]: https://elixir.bootlin.com/linux/latest/source/include/linux/lsm_hook_defs.h
+#[derive(Debug)]
+#[doc(alias = "BPF_PROG_TYPE_LSM")]
+pub struct LsmCgroup {
+    pub(crate) data: ProgramData<LsmLink>,
+}
+
+impl LsmCgroup {
+    /// Loads the program inside the kernel.
+    ///
+    /// # Arguments
+    ///
+    /// * `lsm_hook_name` - full name of the LSM hook that the program should
+    ///   be attached to
+    pub fn load(&mut self, lsm_hook_name: &str, btf: &Btf) -> Result<(), ProgramError> {
+        self.data.expected_attach_type = Some(BPF_LSM_CGROUP);
+        let type_name = format!("bpf_lsm_{lsm_hook_name}");
+        self.data.attach_btf_id =
+            Some(btf.id_by_type_name_kind(type_name.as_str(), BtfKind::Func)?);
+        load_program(BPF_PROG_TYPE_LSM, &mut self.data)
+    }
+
+    /// Attaches the program.
+    ///
+    /// The returned value can be used to detach, see [LsmCgroup::detach].
+    pub fn attach<T: AsFd>(&mut self, cgroup: T) -> Result<LsmLinkId, ProgramError> {
+        let prog_fd = self.fd()?;
+        let prog_fd = prog_fd.as_fd();
+        let cgroup_fd = cgroup.as_fd();
+        let attach_type = self.data.expected_attach_type.unwrap();
+        let btf_id = self.data.attach_btf_id.ok_or(ProgramError::NotLoaded)?;
+        let link_fd = bpf_link_create(
+            prog_fd,
+            LinkTarget::Fd(cgroup_fd),
+            attach_type,
+            0,
+            Some(BpfLinkCreateArgs::TargetBtfId(btf_id)),
+        )
+        .map_err(|(_, io_error)| SyscallError {
+            call: "bpf_link_create",
+            io_error,
+        })?;
+
+        self.data.links.insert(LsmLink::new(FdLink::new(link_fd)))
+    }
+}
+
+define_link_wrapper!(
+    /// The link used by [LsmCgroup] programs.
+    LsmLink,
+    /// The type returned by [LsmCgroup::attach]. Can be passed to [LsmCgroup::detach].
+    LsmLinkId,
+    FdLink,
+    FdLinkId,
+    LsmCgroup,
+);