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Make setjmp/longjmp more secure

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This commit is contained in:
Syrus 2018-12-18 23:21:18 -08:00
parent e278bd4a29
commit db93d2693d
2 changed files with 19 additions and 4 deletions
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19
src/apis/emscripten/jmp.rs
View File

@ -1,12 +1,21 @@
use crate::webassembly::Instance;
use libc::{c_int, c_void};
use std::cell::UnsafeCell;
/// setjmp
pub extern "C" fn __setjmp(env_addr: u32, instance: &mut Instance) -> c_int {
debug!("emscripten::__setjmp (setjmp)");
unsafe {
let env = instance.memory_offset_addr(0, env_addr as usize) as *mut c_void;
setjmp(env)
// Rather than using the env as the holder of the jump address,
// we obscure that id so we are in complete control of it
let obscure_env = instance.memory_offset_addr(0, env_addr as usize) as *mut i8;
let jmp_buf: UnsafeCell<[c_int; 27]> = UnsafeCell::new([0; 27]);
let mut jumps = &mut instance.emscripten_data.as_mut().unwrap().jumps;
let result = setjmp(jmp_buf.get() as _);
*obscure_env = jumps.len() as _;
jumps.push(jmp_buf);
// We use the index of the jump as the jump buffer (env)
result
}
}
@ -14,8 +23,10 @@ pub extern "C" fn __setjmp(env_addr: u32, instance: &mut Instance) -> c_int {
pub extern "C" fn __longjmp(env_addr: u32, val: c_int, instance: &mut Instance) -> ! {
debug!("emscripten::__longjmp (longjmp) {}", val);
unsafe {
let env = instance.memory_offset_addr(0, env_addr as usize) as *mut c_void;
longjmp(env, val)
let obscure_env = instance.memory_offset_addr(0, env_addr as usize) as *mut i8;
let mut jumps = &mut instance.emscripten_data.as_mut().unwrap().jumps;
let mut real_env = &jumps[*obscure_env as usize];
longjmp(real_env.get() as _, val)
};
}

4
src/webassembly/instance.rs
View File

@ -15,7 +15,9 @@ use cranelift_wasm::{FuncIndex, GlobalInit};
use indicatif::{ProgressBar, ProgressStyle};
use rayon::prelude::*;
use libc::c_int;
use region;
use std::cell::UnsafeCell;
use std::iter::FromIterator;
use std::iter::Iterator;
use std::mem::size_of;
@ -72,6 +74,7 @@ pub struct EmscriptenData {
pub memalign: extern "C" fn(u32, u32, &mut Instance) -> u32,
pub memset: extern "C" fn(u32, i32, u32, &mut Instance) -> u32,
pub stack_alloc: extern "C" fn(u32, &Instance) -> u32,
pub jumps: Vec<UnsafeCell<[c_int; 27]>>,
}
impl EmscriptenData {
@ -116,6 +119,7 @@ impl EmscriptenData {
memalign: mem::transmute(memalign_addr),
memset: mem::transmute(memset_addr),
stack_alloc: mem::transmute(stack_alloc_addr),
jumps: Vec::new(),
}
}
}