Fixes the appended use-after-free. The root cause is that
during tb invalidation we use CPU_FOREACH, and therefore
to safely free a vCPU we must wait for an RCU grace period
to elapse.
$ x86_64-linux-user/qemu-x86_64 tests/tcg/x86_64-linux-user/munmap-pthread
=================================================================
==1800604==ERROR: AddressSanitizer: heap-use-after-free on address
0x62d0005f7418 at pc 0x5593da6704eb bp 0x7f4961a7ac70 sp 0x7f4961a7ac60
READ of size 8 at 0x62d0005f7418 thread T2
#0 0x5593da6704ea in tb_jmp_cache_inval_tb ../accel/tcg/tb-maint.c:244
#1 0x5593da6704ea in do_tb_phys_invalidate ../accel/tcg/tb-maint.c:290
#2 0x5593da670631 in tb_phys_invalidate__locked ../accel/tcg/tb-maint.c:306
#3 0x5593da670631 in tb_invalidate_phys_page_range__locked
../accel/tcg/tb-maint.c:542
#4 0x5593da67106d in tb_invalidate_phys_range ../accel/tcg/tb-maint.c:614
#5 0x5593da6a64d4 in target_munmap ../linux-user/mmap.c:766
#6 0x5593da6dba05 in do_syscall1 ../linux-user/syscall.c:10105
#7 0x5593da6f564c in do_syscall ../linux-user/syscall.c:13329
#8 0x5593da49e80c in cpu_loop ../linux-user/x86_64/../i386/cpu_loop.c:233
#9 0x5593da6be28c in clone_func ../linux-user/syscall.c:6633
#10 0x7f496231cb42 in start_thread nptl/pthread_create.c:442
#11 0x7f49623ae9ff (/lib/x86_64-linux-gnu/libc.so.6+0x1269ff)
0x62d0005f7418 is located 28696 bytes inside of 32768-byte region
[0x62d0005f0400,0x62d0005f8400)
freed by thread T148 here:
#0 0x7f49627b6460 in __interceptor_free
../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52
#1 0x5593da5ac057 in cpu_exec_unrealizefn ../cpu.c:180
#2 0x5593da81f851 (/home/cota/src/qemu/build/qemu-x86_64+0x484851)
Signed-off-by: Emilio Cota <c...@braap.org>
---
accel/tcg/cpu-exec.c | 1 -
cpu.c | 7 +++++++
include/hw/core/cpu.h | 3 +++
3 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 356fe348de..ca95d21528 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -1070,7 +1070,6 @@ void tcg_exec_unrealizefn(CPUState *cpu)
#endif /* !CONFIG_USER_ONLY */
tlb_destroy(cpu);
- g_free(cpu->tb_jmp_cache);
}
#ifndef CONFIG_USER_ONLY
diff --git a/cpu.c b/cpu.c
index 4a7d865427..564200559f 100644
--- a/cpu.c
+++ b/cpu.c
@@ -164,6 +164,12 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
#endif /* CONFIG_USER_ONLY */
}
+static void cpu_free_rcu(CPUState *cpu)
+{
+ /* .tb_jmp_cache is NULL except under TCG */
+ g_free(cpu->tb_jmp_cache);
+}
+
void cpu_exec_unrealizefn(CPUState *cpu)
{
#ifndef CONFIG_USER_ONLY
@@ -181,6 +187,7 @@ void cpu_exec_unrealizefn(CPUState *cpu)
}
cpu_list_remove(cpu);
+ call_rcu(cpu, cpu_free_rcu, rcu);
}
/*
diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 8830546121..9fefad5656 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -266,6 +266,7 @@ struct qemu_work_item;
/**
* CPUState:
+ * @rcu: Used for safe deferred memory reclamation.
* @cpu_index: CPU index (informative).
* @cluster_index: Identifies which cluster this CPU is in.
* For boards which don't define clusters or for "loose" CPUs not assigned
@@ -321,6 +322,8 @@ struct qemu_work_item;
* State of one CPU core or thread.
*/
struct CPUState {
+ struct rcu_head rcu;
+
/*< private >*/
DeviceState parent_obj;
/* cache to avoid expensive CPU_GET_CLASS */
--
2.34.1
