commit a51c6f07a896f102930f6f0b60b87036a7bbd6c6
author David Brazdil <dbrazdil@google.com> Wed Oct 12 09:51:48 2022 +0000
committer David Brazdil <dbrazdil@google.com> Wed Oct 12 11:36:58 2022 +0000
tree 351e78d8201c91681f4ea1b12c1b5e5a1a864bcf
parent 8b38f3a7cb0c03005b5a05624f7f54e73d9b6ee2

vmbase: Support LLVM and Bionic stack guard

C code compiled with the Android toolchain has stack guard checks
enabled. So as to avoid having to recompile every target with
-fno-stack-guard, instead add the expected symbols to vmbase.

This means we need __stack_chk_guard variable containing the canary
(used by all libc implementations [1]) and a thread-local storage containing
another copy of the canary at offset 40 (Bionic only [2]).

If the instrumentation detects an error, it calls __stack_chk_fail.
Provide an implementation that simply panics.

[1] bionic/tests/stack_protector_test.cpp
[2] https://reviews.llvm.org/D18632

Bug: 237372981
Test: atest vmbase_example.integration_test
Change-Id: I00de7c75aef6a57a73667df6983a12b01fbe9e51

vmbase/example/src/layout.rs

diff --git a/vmbase/example/src/layout.rs b/vmbase/example/src/layout.rs
index 9cf1a69..463738e 100644
--- a/vmbase/example/src/layout.rs
+++ b/vmbase/example/src/layout.rs
@@ -15,6 +15,7 @@
 //! Memory layout.
 
 use aarch64_paging::paging::{MemoryRegion, VirtualAddress};
+use core::arch::asm;
 use core::ops::Range;
 use vmbase::println;
 
@@ -106,6 +107,21 @@
     );
 }
 
+/// Bionic-compatible thread-local storage entry, at the given offset from TPIDR_EL0.
+pub fn bionic_tls(off: usize) -> u64 {
+    let mut base: usize;
+    unsafe {
+        asm!("mrs {base}, tpidr_el0", base = out(reg) base);
+        let ptr = (base + off) as *const u64;
+        *ptr
+    }
+}
+
+/// Value of __stack_chk_guard.
+pub fn stack_chk_guard() -> u64 {
+    unsafe { __stack_chk_guard }
+}
+
 extern "C" {
     static dtb_begin: u8;
     static dtb_end: u8;
@@ -120,4 +136,5 @@
     static bss_end: u8;
     static boot_stack_begin: u8;
     static boot_stack_end: u8;
+    static __stack_chk_guard: u64;
 }

vmbase/example/src/main.rs

diff --git a/vmbase/example/src/main.rs b/vmbase/example/src/main.rs
index 3c91f97..9b362b2 100644
--- a/vmbase/example/src/main.rs
+++ b/vmbase/example/src/main.rs
@@ -24,7 +24,8 @@
 extern crate alloc;
 
 use crate::layout::{
-    dtb_range, print_addresses, rodata_range, text_range, writable_region, DEVICE_REGION,
+    bionic_tls, dtb_range, print_addresses, rodata_range, stack_chk_guard, text_range,
+    writable_region, DEVICE_REGION,
 };
 use aarch64_paging::{idmap::IdMap, paging::Attributes};
 use alloc::{vec, vec::Vec};
@@ -55,6 +56,7 @@
     print_addresses();
     assert_eq!(arg0, dtb_range().start.0 as u64);
     check_data();
+    check_stack_guard();
 
     unsafe {
         HEAP_ALLOCATOR.lock().init(&mut HEAP as *mut u8 as usize, HEAP.len());
@@ -94,6 +96,13 @@
     check_data();
 }
 
+fn check_stack_guard() {
+    const BIONIC_TLS_STACK_GRD_OFF: usize = 40;
+
+    info!("Testing stack guard");
+    assert_eq!(bionic_tls(BIONIC_TLS_STACK_GRD_OFF), stack_chk_guard());
+}
+
 fn check_data() {
     info!("INITIALISED_DATA: {:#010x}", &INITIALISED_DATA as *const u32 as usize);
     unsafe {