/* serve trap invoked from the untrusted code */
NORETURN void SyscallHook()
{
struct NaClApp *nap;
struct ThreadContext *user;
uintptr_t tramp_ret;
nacl_reg_t user_ret;
size_t sysnum;
uintptr_t sp_user;
uintptr_t sp_sys;
/* restore trusted side environment */
nap = gnap; /* restore NaClApp object */
user = nacl_user;
sp_user = GetThreadCtxSp(user);
sp_sys = sp_user;
/*
* sp_sys points to the top of user stack where there is a retaddr to
* trampoline slot
*/
tramp_ret = *(uintptr_t *)sp_sys;
sysnum = (tramp_ret - (nap->mem_start + NACL_SYSCALL_START_ADDR))
>> NACL_SYSCALL_BLOCK_SHIFT;
/*
* getting user return address (the address where we need to return after
* system call) from the user stack. (see stack layout above)
*/
user_ret = *(uintptr_t *)(sp_sys + NACL_USERRET_FIX);
/*
* Fix the user stack, throw away return addresses from the top of the stack.
* After this fix, the first argument to a system call must be on the top of
* the user stack (see user stack layout above)
*/
sp_sys += NACL_SYSARGS_FIX;
sp_user += NACL_SYSCALLRET_FIX;
SetThreadCtxSp(user, sp_user);
/* fail if nacl syscall received */
ZLOGFAIL(sysnum != 0, EINVAL, "nacl syscall #%d received", sysnum);
/*
* syscall_args must point to the first argument of a system call.
* System call arguments are placed on the untrusted user stack.
*/
nap->sysret = TrapHandler(nap, *(uint32_t*)sp_sys);
/*
* before switching back to user module, we need to make sure that the
* user_ret is properly sandboxed.
*/
user_ret = (nacl_reg_t)NaClSandboxCodeAddr(nap, (uintptr_t)user_ret);
/* d'b: give control to the user side */
SwitchToApp(nap, user_ret);
ZLOGFAIL(1, EFAULT, "the unreachable has been reached");
}
__cdecl
Exhandler(EXCEPTION_RECORD *rec, void *frame, CONTEXT *context, void *dcon)
{
EXCEPTION_POINTERS ep;
ep.ExceptionRecord = rec;
ep.ContextRecord = context;
TrapHandler(&ep);
return ExceptionContinueExecution;
}
/* d'b: trap(). see documentation for the details */
static int32_t TrapDecoder(struct NaClApp *nap)
{
struct TrapDecoderArgs
{
uint32_t args;
} p = *(struct TrapDecoderArgs*) nap->syscall_args;
return TrapHandler(nap, p.args);
}
