There are some situations where the guest application changes the SIGSEGV and
messes with qemu-user way of handling self-modifying code.
In case of qemu-system, this happens. Emulation of qemu-system inside qemu-user
doesn't work because of this. This patch doesn't aim to do a complete signal
protection and achieve bulletproof signal management for every test case,
instead it is a small easy-to-understand patch that resolves the most common
problem.
Signed-off-by: Alex Barcelo <abarc...@ac.upc.edu>
---
linux-user/syscall.c | 18 ++++++++++++++++++
1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 6257a04..95bb818 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5897,6 +5897,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long
arg1,
}
break;
#endif
+
+/*
+ * Use SETSIGNAL and GETSIGNAL macros for SIGSEGV protection.
+ *
+ * This should protect SIGSEGV unconscious manipulations from guest apps
+ * (but we still do not let the emulated software play the signal game)
+ */
+#define SETSIGNAL(set) sigdelset( (set), SIGSEGV)
+#define GETSIGNAL(get) sigaddset( (get), SIGSEGV)
+
#ifdef TARGET_NR_sigprocmask
case TARGET_NR_sigprocmask:
{
@@ -5952,6 +5962,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
target_to_host_old_sigset(&set, p);
unlock_user(p, arg2, 0);
set_ptr = &set;
+ // override SIGSEGV when changing mask
+ SETSIGNAL(set_ptr);
} else {
how = 0;
set_ptr = NULL;
@@ -5960,6 +5972,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
if (!is_error(ret) && arg3) {
if (!(p = lock_user(VERIFY_WRITE, arg3,
sizeof(target_sigset_t), 0)))
goto efault;
+ // ignore real SIGSEGV state in mask
+ GETSIGNAL(&oldset);
host_to_target_old_sigset(p, &oldset);
unlock_user(p, arg3, sizeof(target_sigset_t));
}
@@ -5992,6 +6006,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
target_to_host_sigset(&set, p);
unlock_user(p, arg2, 0);
set_ptr = &set;
+ // override SIGSEGV when changing mask
+ SETSIGNAL(set_ptr);
} else {
how = 0;
set_ptr = NULL;
@@ -6001,6 +6017,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
if (!(p = lock_user(VERIFY_WRITE, arg3,
sizeof(target_sigset_t), 0)))
goto efault;
host_to_target_sigset(p, &oldset);
+ // ignore real SIGSEGV state in mask
+ GETSIGNAL(&oldset);
unlock_user(p, arg3, sizeof(target_sigset_t));
}
}
--
1.7.5.4
