1 //===-- working_set_posix.cpp -----------------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file is a part of EfficiencySanitizer, a family of performance tuners.
11 //
12 // POSIX-specific working set tool code.
13 //===----------------------------------------------------------------------===//
14 
15 #include "working_set.h"
16 #include "esan_flags.h"
17 #include "esan_shadow.h"
18 #include "sanitizer_common/sanitizer_common.h"
19 #include "sanitizer_common/sanitizer_linux.h"
20 #include <signal.h>
21 #include <sys/mman.h>
22 
23 namespace __esan {
24 
25 // We only support regular POSIX threads with a single signal handler
26 // for the whole process == thread group.
27 // Thus we only need to store one app signal handler.
28 // FIXME: Store and use any alternate stack and signal flags set by
29 // the app.  For now we just call the app handler from our handler.
30 static __sanitizer_sigaction AppSigAct;
31 
32 bool processWorkingSetSignal(int SigNum, void (*Handler)(int),
33                              void (**Result)(int)) {
34   VPrintf(2, "%s: %d\n", __FUNCTION__, SigNum);
35   if (SigNum == SIGSEGV) {
36     *Result = AppSigAct.handler;
37     AppSigAct.sigaction = (decltype(AppSigAct.sigaction))Handler;
38     return false; // Skip real call.
39   }
40   return true;
41 }
42 
43 bool processWorkingSetSigaction(int SigNum, const void *ActVoid,
44                                 void *OldActVoid) {
45   VPrintf(2, "%s: %d\n", __FUNCTION__, SigNum);
46   if (SigNum == SIGSEGV) {
47     const struct sigaction *Act = (const struct sigaction *) ActVoid;
48     struct sigaction *OldAct = (struct sigaction *) OldActVoid;
49     if (OldAct)
50       internal_memcpy(OldAct, &AppSigAct, sizeof(OldAct));
51     if (Act)
52       internal_memcpy(&AppSigAct, Act, sizeof(AppSigAct));
53     return false; // Skip real call.
54   }
55   return true;
56 }
57 
58 bool processWorkingSetSigprocmask(int How, void *Set, void *OldSet) {
59   VPrintf(2, "%s\n", __FUNCTION__);
60   // All we need to do is ensure that SIGSEGV is not blocked.
61   // FIXME: we are not fully transparent as we do not pretend that
62   // SIGSEGV is still blocked on app queries: that would require
63   // per-thread mask tracking.
64   if (Set && (How == SIG_BLOCK || How == SIG_SETMASK)) {
65     if (internal_sigismember((__sanitizer_sigset_t *)Set, SIGSEGV)) {
66       VPrintf(1, "%s: removing SIGSEGV from the blocked set\n", __FUNCTION__);
67       internal_sigdelset((__sanitizer_sigset_t *)Set, SIGSEGV);
68     }
69   }
70   return true;
71 }
72 
73 static void reinstateDefaultHandler(int SigNum) {
74   __sanitizer_sigaction SigAct;
75   internal_memset(&SigAct, 0, sizeof(SigAct));
76   SigAct.sigaction = (decltype(SigAct.sigaction))SIG_DFL;
77   int Res = internal_sigaction(SigNum, &SigAct, nullptr);
78   CHECK(Res == 0);
79   VPrintf(1, "Unregistered for %d handler\n", SigNum);
80 }
81 
82 // If this is a shadow fault, we handle it here; otherwise, we pass it to the
83 // app to handle it just as the app would do without our tool in place.
84 static void handleMemoryFault(int SigNum, __sanitizer_siginfo *Info,
85                               void *Ctx) {
86   if (SigNum == SIGSEGV) {
87     // We rely on si_addr being filled in (thus we do not support old kernels).
88     siginfo_t *SigInfo = (siginfo_t *)Info;
89     uptr Addr = (uptr)SigInfo->si_addr;
90     if (isShadowMem(Addr)) {
91       VPrintf(3, "Shadow fault @%p\n", Addr);
92       uptr PageSize = GetPageSizeCached();
93       int Res = internal_mprotect((void *)RoundDownTo(Addr, PageSize),
94                                   PageSize, PROT_READ|PROT_WRITE);
95       CHECK(Res == 0);
96     } else if (AppSigAct.sigaction) {
97       // FIXME: For simplicity we ignore app options including its signal stack
98       // (we just use ours) and all the delivery flags.
99       AppSigAct.sigaction(SigNum, Info, Ctx);
100     } else {
101       // Crash instead of spinning with infinite faults.
102       reinstateDefaultHandler(SigNum);
103     }
104   } else
105     UNREACHABLE("signal not registered");
106 }
107 
108 void registerMemoryFaultHandler() {
109   // We do not use an alternate signal stack, as doing so would require
110   // setting it up for each app thread.
111   // FIXME: This could result in problems with emulating the app's signal
112   // handling if the app relies on an alternate stack for SIGSEGV.
113 
114   // We require that SIGSEGV is not blocked.  We use a sigprocmask
115   // interceptor to ensure that in the future.  Here we ensure it for
116   // the current thread.  We assume there are no other threads at this
117   // point during initialization, or that at least they do not block
118   // SIGSEGV.
119   __sanitizer_sigset_t SigSet;
120   internal_sigemptyset(&SigSet);
121   internal_sigprocmask(SIG_BLOCK, &SigSet, nullptr);
122 
123   __sanitizer_sigaction SigAct;
124   internal_memset(&SigAct, 0, sizeof(SigAct));
125   SigAct.sigaction = handleMemoryFault;
126   // We want to handle nested signals b/c we need to handle a
127   // shadow fault in an app signal handler.
128   SigAct.sa_flags = SA_SIGINFO | SA_NODEFER;
129   int Res = internal_sigaction(SIGSEGV, &SigAct, &AppSigAct);
130   CHECK(Res == 0);
131   VPrintf(1, "Registered for SIGSEGV handler\n");
132 }
133 
134 } // namespace __esan
135