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aya-bpf/helpers: add documentation and implement all bpf_probe_read_* wrappers

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This patch adds some documentation to aya-bpf/helpers and adds documentation
for the module itself and for all of the wrappers currently defined in the module.

It also implements the rest of the bpf_probe_read_* wrappers that were missing from this
file. In the future, it probably also makes sense to add some bpf_probe_read_* wrappers
that can read directly into a map pointer, avoiding the BPF stack altogether. I'm going to
call this out of scope for this PR, but plan to submit a subsequent one that addresses
this use case.

Signed-off-by: William Findlay <william@williamfindlay.com>
ci
William Findlay 3 years ago committed by Alessandro Decina
parent b13fe98080
commit e94e988336
1 changed files with 259 additions and 0 deletions
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259
bpf/aya-bpf/src/helpers.rs
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@ -1,3 +1,12 @@
//! This module contains kernel helper functions that may be exposed to specific BPF
//! program types. These helpers can be used to perform common tasks, query and operate on
//! data exposed by the kernel, and perform some operations that would normally be denied
//! by the BPF verifier.
//!
//! Here, we provide some higher-level wrappers around the underlying kernel helpers, but
//! also expose bindings to the underlying helpers as a fall-back in case of a missing
//! implementation.
use core::mem::{self, MaybeUninit};
pub use aya_bpf_bindings::helpers as gen;
@ -5,6 +14,31 @@ pub use gen::*;
use crate::cty::{c_char, c_long, c_void};
/// Read bytes stored at `src` and store them as a `T`.
///
/// Generally speaking, the more specific [`bpf_probe_read_user`] and
/// [`bpf_probe_read_kernel`] should be preferred over this function.
///
/// Returns a bitwise copy of `mem::size_of::<T>()` bytes stored at the user space address
/// `src`. See `bpf_probe_read_kernel` for reading kernel space memory.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::{c_int, c_long}, helpers::bpf_probe_read};
/// # fn try_test() -> Result<(), c_long> {
/// # let kernel_ptr: *const c_int = 0 as _;
/// let my_int: c_int = unsafe { bpf_probe_read(kernel_ptr)? };
///
/// // Do something with my_int
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns a negative value wrapped in an `Err`.
#[inline]
pub unsafe fn bpf_probe_read<T>(src: *const T) -> Result<T, c_long> {
let mut v: MaybeUninit<T> = MaybeUninit::uninit();
@ -20,6 +54,149 @@ pub unsafe fn bpf_probe_read<T>(src: *const T) -> Result<T, c_long> {
Ok(v.assume_init())
}
/// Read bytes stored at the _user space_ pointer `src` and store them as a `T`.
///
/// Returns a bitwise copy of `mem::size_of::<T>()` bytes stored at the user space address
/// `src`. See `bpf_probe_read_kernel` for reading kernel space memory.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::{c_int, c_long}, helpers::bpf_probe_read_user};
/// # fn try_test() -> Result<(), c_long> {
/// # let user_ptr: *const c_int = 0 as _;
/// let my_int: c_int = unsafe { bpf_probe_read_user(user_ptr)? };
///
/// // Do something with my_int
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns a negative value wrapped in an `Err`.
#[inline]
pub unsafe fn bpf_probe_read_user<T>(src: *const T) -> Result<T, c_long> {
let mut v: MaybeUninit<T> = MaybeUninit::uninit();
let ret = gen::bpf_probe_read_user(
v.as_mut_ptr() as *mut c_void,
mem::size_of::<T>() as u32,
src as *const c_void,
);
if ret < 0 {
return Err(ret);
}
Ok(v.assume_init())
}
/// Read bytes stored at the _kernel space_ pointer `src` and store them as a `T`.
///
/// Returns a bitwise copy of `mem::size_of::<T>()` bytes stored at the kernel space address
/// `src`. See `bpf_probe_read_user` for reading user space memory.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::{c_int, c_long}, helpers::bpf_probe_read_kernel};
/// # fn try_test() -> Result<(), c_long> {
/// # let kernel_ptr: *const c_int = 0 as _;
/// let my_int: c_int = unsafe { bpf_probe_read_kernel(kernel_ptr)? };
///
/// // Do something with my_int
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns a negative value wrapped in an `Err`.
#[inline]
pub unsafe fn bpf_probe_read_kernel<T>(src: *const T) -> Result<T, c_long> {
let mut v: MaybeUninit<T> = MaybeUninit::uninit();
let ret = gen::bpf_probe_read_kernel(
v.as_mut_ptr() as *mut c_void,
mem::size_of::<T>() as u32,
src as *const c_void,
);
if ret < 0 {
return Err(ret);
}
Ok(v.assume_init())
}
/// Read a null-terminated string stored at `src` into `dest`.
///
/// Generally speaking, the more specific [`bpf_probe_read_user_str`] and
/// [`bpf_probe_read_kernel_str`] should be preferred over this function.
///
/// In case the length of `dest` is smaller then the length of `src`, the read bytes will
/// be truncated to the size of `dest`.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::c_long, helpers::bpf_probe_read_str};
/// # fn try_test() -> Result<(), c_long> {
/// # let kernel_ptr: *const u8 = 0 as _;
/// let mut my_str = [0u8; 16];
/// let num_read = unsafe { bpf_probe_read_str(kernel_ptr, &mut my_str)? };
///
/// // Do something with num_read and my_str
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns Err(-1).
#[inline]
pub unsafe fn bpf_probe_read_str(src: *const u8, dest: &mut [u8]) -> Result<usize, c_long> {
let len = gen::bpf_probe_read_str(
dest.as_mut_ptr() as *mut c_void,
dest.len() as u32,
src as *const c_void,
);
if len < 0 {
return Err(-1);
}
let mut len = len as usize;
if len > dest.len() {
// this can never happen, it's needed to tell the verifier that len is
// bounded
len = dest.len();
}
Ok(len as usize)
}
/// Read a null-terminated string from _user space_ stored at `src` into `dest`.
///
/// In case the length of `dest` is smaller then the length of `src`, the read bytes will
/// be truncated to the size of `dest`.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::c_long, helpers::bpf_probe_read_user_str};
/// # fn try_test() -> Result<(), c_long> {
/// # let user_ptr: *const u8 = 0 as _;
/// let mut my_str = [0u8; 16];
/// let num_read = unsafe { bpf_probe_read_user_str(user_ptr, &mut my_str)? };
///
/// // Do something with num_read and my_str
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns Err(-1).
#[inline]
pub unsafe fn bpf_probe_read_user_str(src: *const u8, dest: &mut [u8]) -> Result<usize, c_long> {
let len = gen::bpf_probe_read_user_str(
@ -40,6 +217,65 @@ pub unsafe fn bpf_probe_read_user_str(src: *const u8, dest: &mut [u8]) -> Result
Ok(len as usize)
}
/// Read a null-terminated string from _kernel space_ stored at `src` into `dest`.
///
/// In case the length of `dest` is smaller then the length of `src`, the read bytes will
/// be truncated to the size of `dest`.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf::{cty::c_long, helpers::bpf_probe_read_kernel_str};
/// # fn try_test() -> Result<(), c_long> {
/// # let kernel_ptr: *const u8 = 0 as _;
/// let mut my_str = [0u8; 16];
/// let num_read = unsafe { bpf_probe_read_kernel_str(kernel_ptr, &mut my_str)? };
///
/// // Do something with num_read and my_str
/// # Ok::<(), c_long>(())
/// # }
/// ```
///
/// # Errors
///
/// On failure, this function returns Err(-1).
#[inline]
pub unsafe fn bpf_probe_read_kernel_str(src: *const u8, dest: &mut [u8]) -> Result<usize, c_long> {
let len = gen::bpf_probe_read_kernel_str(
dest.as_mut_ptr() as *mut c_void,
dest.len() as u32,
src as *const c_void,
);
if len < 0 {
return Err(-1);
}
let mut len = len as usize;
if len > dest.len() {
// this can never happen, it's needed to tell the verifier that len is
// bounded
len = dest.len();
}
Ok(len as usize)
}
/// Read the `comm` field associated with the current task struct
/// as a `[c_char; 16]`.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf:: helpers::bpf_get_current_comm;
/// let comm = bpf_get_current_comm();
///
/// // Do something with comm
/// ```
///
/// # Errors
///
/// On failure, this function returns a negative value wrapped in an `Err`.
#[inline]
pub fn bpf_get_current_comm() -> Result<[c_char; 16], c_long> {
let mut comm: [c_char; 16usize] = [0; 16];
@ -51,6 +287,29 @@ pub fn bpf_get_current_comm() -> Result<[c_char; 16], c_long> {
}
}
/// Read the process id and thread group id associated with the current task struct as
/// a `u64`.
///
/// In the return value, the upper 32 bits are the `tgid`, and the lower 32 bits are the
/// `pid`. That is, the returned value is equal to: `(tgid << 32) | pid`. A caller may
/// access the individual fields by either casting to a `u32` or performing a `>> 32` bit
/// shift and casting to a `u32`.
///
/// Note that the naming conventions used in the kernel differ from user space. From the
/// perspective of user space, `pid` may be thought of as the thread id, and `tgid` may be
/// thought of as the process id. For single-threaded processes, these values are
/// typically the same.
///
/// # Examples
///
/// ```no_run
/// # #![allow(dead_code)]
/// # use aya_bpf:: helpers::bpf_get_current_pid_tgid;
/// let tgid = (bpf_get_current_pid_tgid() >> 32) as u32;
/// let pid = bpf_get_current_pid_tgid() as u32;
///
/// // Do something with pid and tgid
/// ```
#[inline]
pub fn bpf_get_current_pid_tgid() -> u64 {
unsafe { gen::bpf_get_current_pid_tgid() }

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