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Rollup merge of #78785 - cuviper:weak-getrandom, r=m-ou-se

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linux: try to use libc getrandom to allow interposition

We'll try to use a weak `getrandom` symbol first, because that allows
things like `LD_PRELOAD` interposition. For example, perf measurements
might want to disable randomness to get reproducible results. If the
weak symbol is not found, we fall back to a raw `SYS_getrandom` call.
This commit is contained in:
Mara Bos 2020-11-18 15:46:23 +01:00 committed by GitHub
commit 61134aa54c
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3 changed files with 35 additions and 18 deletions
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18
library/std/src/sys/unix/kernel_copy.rs
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@ -445,15 +445,15 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
// We store the availability in a global to avoid unnecessary syscalls
static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);
unsafe fn copy_file_range(
fd_in: libc::c_int,
off_in: *mut libc::loff_t,
fd_out: libc::c_int,
off_out: *mut libc::loff_t,
len: libc::size_t,
flags: libc::c_uint,
) -> libc::c_long {
libc::syscall(libc::SYS_copy_file_range, fd_in, off_in, fd_out, off_out, len, flags)
syscall! {
fn copy_file_range(
fd_in: libc::c_int,
off_in: *mut libc::loff_t,
fd_out: libc::c_int,
off_out: *mut libc::loff_t,
len: libc::size_t,
flags: libc::c_uint
) -> libc::ssize_t
}
let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);

15
library/std/src/sys/unix/rand.rs
View File

@ -25,10 +25,19 @@ mod imp {
use crate::io::Read;
#[cfg(any(target_os = "linux", target_os = "android"))]
fn getrandom(buf: &mut [u8]) -> libc::c_long {
unsafe {
libc::syscall(libc::SYS_getrandom, buf.as_mut_ptr(), buf.len(), libc::GRND_NONBLOCK)
fn getrandom(buf: &mut [u8]) -> libc::ssize_t {
// A weak symbol allows interposition, e.g. for perf measurements that want to
// disable randomness for consistency. Otherwise, we'll try a raw syscall.
// (`getrandom` was added in glibc 2.25, musl 1.1.20, android API level 28)
syscall! {
fn getrandom(
buffer: *mut libc::c_void,
length: libc::size_t,
flags: libc::c_uint
) -> libc::ssize_t
}
unsafe { getrandom(buf.as_mut_ptr().cast(), buf.len(), libc::GRND_NONBLOCK) }
}
#[cfg(not(any(target_os = "linux", target_os = "android")))]

20
library/std/src/sys/unix/weak.rs
View File

@ -66,7 +66,7 @@ unsafe fn fetch(name: &str) -> usize {
libc::dlsym(libc::RTLD_DEFAULT, name.as_ptr()) as usize
}
#[cfg(not(target_os = "linux"))]
#[cfg(not(any(target_os = "linux", target_os = "android")))]
macro_rules! syscall {
(fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
unsafe fn $name($($arg_name: $t),*) -> $ret {
@ -84,7 +84,7 @@ macro_rules! syscall {
)
}
#[cfg(target_os = "linux")]
#[cfg(any(target_os = "linux", target_os = "android"))]
macro_rules! syscall {
(fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
unsafe fn $name($($arg_name:$t),*) -> $ret {
@ -92,10 +92,18 @@ macro_rules! syscall {
// (not paths).
use libc::*;
syscall(
concat_idents!(SYS_, $name),
$($arg_name as c_long),*
) as $ret
weak! { fn $name($($t),*) -> $ret }
// Use a weak symbol from libc when possible, allowing `LD_PRELOAD`
// interposition, but if it's not found just use a raw syscall.
if let Some(fun) = $name.get() {
fun($($arg_name),*)
} else {
syscall(
concat_idents!(SYS_, $name),
$($arg_name as c_long),*
) as $ret
}
}
)
}