x86_64: Add fixup code if previous RIP was invalid (#120)

* x86_64: Add fixup code if previous RIP was invalid

Previous RIP could become invalid if a bad function pointer
was followed. Calling unwind from a signal frame in this case
skips the frame that called the bad pointer.

Check if the value at RSP looks to be valid in this case. It
should be the value of RIP pushed to the stack by the CALL instruction.
If it looks valid use this value as the next frames RIP else fallback
to the previous method.

4 files changed, 210 insertions, 30 deletions

diff --git a/.gitignore b/.gitignore
index af68f0e6..724a1f48 100644
--- a/.gitignore
+++ b/.gitignore
@@ -76,5 +76,6 @@ tests/[GL]ia64-test-stack
 tests/ia64-test-dyn1
 tests/ia64-test-sig
 tests/[GL]x64-test-dwarf-expressions
+tests/x64-unwind-badjmp-signal-frame
 tests/*.log
 tests/*.trs
diff --git a/src/x86_64/Gstep.c b/src/x86_64/Gstep.c
index 10498170..81e7b09d 100644
--- a/src/x86_64/Gstep.c
+++ b/src/x86_64/Gstep.c
@@ -104,6 +104,7 @@ unw_step (unw_cursor_t *cursor)
               via CALLQ.  Try this for all non-signal trampoline
               code.  */
 
+      unw_word_t invalid_prev_rip = 0;
       unw_word_t prev_ip = c->dwarf.ip, prev_cfa = c->dwarf.cfa;
       struct dwarf_loc rbp_loc, rsp_loc, rip_loc;
 
@@ -149,7 +150,10 @@ unw_step (unw_cursor_t *cursor)
               return ret;
             }
 
-          if (!rbp)
+          unw_word_t not_used;
+          invalid_prev_rip = dwarf_get(&c->dwarf, DWARF_MEM_LOC(c->dwarf, prev_ip), &not_used);
+
+          if (!rbp && invalid_prev_rip == 0)
             {
               /* Looks like we may have reached the end of the call-chain.  */
               rbp_loc = DWARF_NULL_LOC;
@@ -158,38 +162,90 @@ unw_step (unw_cursor_t *cursor)
             }
           else
             {
-              unw_word_t rbp1 = 0;
-              rbp_loc = DWARF_LOC(rbp, 0);
-              rsp_loc = DWARF_NULL_LOC;
-              rip_loc = DWARF_LOC (rbp + 8, 0);
-              ret = dwarf_get (&c->dwarf, rbp_loc, &rbp1);
-              Debug (1, "[RBP=0x%lx] = 0x%lx (cfa = 0x%lx) -> 0x%lx\n",
-                     (unsigned long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
-                     rbp, c->dwarf.cfa, rbp1);
-
-              /* Heuristic to determine incorrect guess.  For RBP to be a
-                 valid frame it needs to be above current CFA, but don't
-                 let it go more than a little.  Note that we can't deduce
-                 anything about new RBP (rbp1) since it may not be a frame
-                 pointer in the frame above.  Just check we get the value. */
-              if (ret < 0
-                  || rbp < c->dwarf.cfa
-                  || (rbp - c->dwarf.cfa) > 0x4000)
+              /*
+               * Check if previous RIP was invalid
+               * This could happen if a bad function pointer was
+               * followed and so the stack wasn't updated by the
+               * preamble
+               */
+              int rip_fixup_success = 0;
+              if (invalid_prev_rip != 0)
                 {
-                  rip_loc = DWARF_NULL_LOC;
-                  rbp_loc = DWARF_NULL_LOC;
-                }
+                    Debug (2, "Previous RIP 0x%lx was invalid, attempting fixup\n", prev_ip);
+                    unw_word_t rsp;
+                    ret = dwarf_get (&c->dwarf, c->dwarf.loc[RSP], &rsp);
 
-              c->frame_info.frame_type = UNW_X86_64_FRAME_GUESSED;
-              c->frame_info.cfa_reg_rsp = 0;
-              c->frame_info.cfa_reg_offset = 16;
-              c->frame_info.rbp_cfa_offset = -16;
-              c->dwarf.cfa += 16;
-            }
+                    /*Test to see if what we think is the previous RIP is valid*/
+                    unw_word_t new_ip = 0;
+                    if (dwarf_get(&c->dwarf, DWARF_MEM_LOC(c->dwarf, rsp), &new_ip) == 0)
+                      {
+                        Debug (2, "RSP 0x%lx looks valid\n", rsp);
+                        if ((ret = dwarf_get(&c->dwarf, DWARF_MEM_LOC(c->dwarf, new_ip), &not_used)) == 0)
+                          {
+                            Debug (2, "new_ip 0x%lx looks valid\n", new_ip);
+                            rip_fixup_success = 1;
+                            c->frame_info.cfa_reg_offset = 8;
+                            c->frame_info.cfa_reg_rsp = 1;
+                            c->frame_info.rbp_cfa_offset = -1;
+                            c->frame_info.rsp_cfa_offset = -1;
+                            c->frame_info.frame_type = UNW_X86_64_FRAME_OTHER;
+                            /*
+                             * The call should have pushed RIP to the stack
+                             * and since there was no preamble RSP hasn't been
+                             * touched so RIP should be at RSP.
+                             */
+                            c->dwarf.cfa += 8;
+                            /* Optimised x64 binaries don't use RBP it seems? */
+                            rbp_loc = DWARF_LOC (rbp, 0);
+                            rsp_loc = DWARF_LOC (rsp, 0);
+                            rip_loc = DWARF_LOC (rsp, 0);
+                          }
+                        else
+                          Debug (2, "new_ip 0x%lx dwarf_get(&c->dwarf, DWARF_MEM_LOC(c->dwarf, new_ip), &not_used) != 0\n", new_ip);
+                      }
+		                else
+                        Debug (2, "rsp 0x%lx dwarf_get(&c->dwarf, DWARF_MEM_LOC(c->dwarf, rsp), &new_ip) != 0\n", rsp);
+                  }
+              /*
+               * If the previous rip we found on the stack didn't look valid fall back
+               * to the previous method for finding a valid stack frame
+               */
+              if (!rip_fixup_success)
+                {
+                  Debug (2, "RIP fixup didn't work, falling back\n");
+                  unw_word_t rbp1 = 0;
+                  rbp_loc = DWARF_LOC(rbp, 0);
+                  rsp_loc = DWARF_NULL_LOC;
+                  rip_loc = DWARF_LOC (rbp + 8, 0);
+                  ret = dwarf_get (&c->dwarf, rbp_loc, &rbp1);
+                  Debug (1, "[RBP=0x%lx] = 0x%lx (cfa = 0x%lx) -> 0x%lx\n",
+                         (unsigned long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
+                         rbp, c->dwarf.cfa, rbp1);
+
+                  /* Heuristic to determine incorrect guess.  For RBP to be a
+                     valid frame it needs to be above current CFA, but don't
+                     let it go more than a little.  Note that we can't deduce
+                     anything about new RBP (rbp1) since it may not be a frame
+                     pointer in the frame above.  Just check we get the value. */
+                  if (ret < 0
+                      || rbp < c->dwarf.cfa
+                      || (rbp - c->dwarf.cfa) > 0x4000)
+                    {
+                      rip_loc = DWARF_NULL_LOC;
+                      rbp_loc = DWARF_NULL_LOC;
+                    }
 
+                  c->frame_info.frame_type = UNW_X86_64_FRAME_GUESSED;
+                  c->frame_info.cfa_reg_rsp = 0;
+                  c->frame_info.cfa_reg_offset = 16;
+                  c->frame_info.rbp_cfa_offset = -16;
+                  c->dwarf.cfa += 16;
+
+                }
+            }
           /* Mark all registers unsaved */
           for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
-            c->dwarf.loc[i] = DWARF_NULL_LOC;
+          c->dwarf.loc[i] = DWARF_NULL_LOC;
 
           c->dwarf.loc[RBP] = rbp_loc;
           c->dwarf.loc[RSP] = rsp_loc;
@@ -197,7 +253,7 @@ unw_step (unw_cursor_t *cursor)
           c->dwarf.use_prev_instr = 1;
         }
 
-      if (DWARF_IS_NULL_LOC (c->dwarf.loc[RBP]))
+      if (DWARF_IS_NULL_LOC (c->dwarf.loc[RBP]) && invalid_prev_rip == 0)
         {
           ret = 0;
           Debug (2, "NULL %%rbp loc, returning %d\n", ret);
diff --git a/tests/Makefile.am b/tests/Makefile.am
index fee8a70b..61d1bf87 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -39,7 +39,7 @@ if USE_ALTIVEC
 endif #USE_ALTIVEC
 else  #!ARCH_PPC64
 if ARCH_X86_64
- check_PROGRAMS_arch +=	Gx64-test-dwarf-expressions Lx64-test-dwarf-expressions
+ check_PROGRAMS_arch +=	Gx64-test-dwarf-expressions Lx64-test-dwarf-expressions x64-unwind-badjmp-signal-frame
 endif #ARCH X86_64
 endif #!ARCH_PPC64
 endif #!ARCH_IA64
@@ -157,6 +157,7 @@ Ltest_cxx_exceptions_SOURCES = Ltest-cxx-exceptions.cxx
 
 Ltest_init_local_signal_SOURCES = Ltest-init-local-signal.c Ltest-init-local-signal-lib.c
 
+x64_unwind_badjmp_signal_frame_SOURCES = x64-unwind-badjmp-signal-frame.c
 Gtest_dyn1_SOURCES = Gtest-dyn1.c flush-cache.S flush-cache.h
 Ltest_dyn1_SOURCES = Ltest-dyn1.c flush-cache.S flush-cache.h
 test_static_link_SOURCES = test-static-link-loc.c test-static-link-gen.c
@@ -203,6 +204,7 @@ Ltest_init_local_signal_LDADD = $(LIBUNWIND) $(LIBUNWIND_local)
 
 Gtest_bt_LDADD = $(LIBUNWIND) $(LIBUNWIND_local)
 Gtest_concurrent_LDADD = $(LIBUNWIND) $(LIBUNWIND_local) -lpthread
+x64_unwind_badjmp_signal_frame_LDADD = $(LIBUNWIND) $(LIBUNWIND_local)
 Gtest_dyn1_LDADD = $(LIBUNWIND) $(LIBUNWIND_local)
 Gtest_exc_LDADD = $(LIBUNWIND) $(LIBUNWIND_local)
 Gtest_init_LDADD = $(LIBUNWIND) $(LIBUNWIND_local) @BACKTRACELIB@
diff --git a/tests/x64-unwind-badjmp-signal-frame.c b/tests/x64-unwind-badjmp-signal-frame.c
new file mode 100644
index 00000000..6b4ea3ac
--- /dev/null
+++ b/tests/x64-unwind-badjmp-signal-frame.c
@@ -0,0 +1,121 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2019 Brock York <twunknown AT gmail.com>
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <string.h>
+#include <execinfo.h>
+#include <sys/types.h>
+#include <sys/ucontext.h>
+#include <unistd.h>
+#include <sys/ptrace.h>
+
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+
+/*
+ * unwind in the signal handler checking the backtrace is correct
+ * after a bad jump.
+ */
+void handle_sigsegv(int signal, siginfo_t *info, void *ucontext)
+{
+  /*
+   * 0 = success
+   * !0 = general failure
+   * 77 = test skipped
+   * 99 = complete failure
+   */
+  int test_status = 0;
+  unw_cursor_t cursor; unw_context_t uc;
+  unw_word_t ip, sp, offset;
+  char name[1000];
+  int found_signal_frame = 0;
+  int i = 0;
+  char *names[] = {
+    "",
+    "main",
+  };
+  int names_count = sizeof(names) / sizeof(*names);
+
+  unw_getcontext(&uc);
+  unw_init_local(&cursor, &uc);
+
+  while (unw_step(&cursor) > 0 && !test_status)
+    {
+      if (unw_is_signal_frame(&cursor))
+        {
+          found_signal_frame = 1;
+        }
+      if (found_signal_frame)
+        {
+          unw_get_reg(&cursor, UNW_REG_IP, &ip);
+          unw_get_reg(&cursor, UNW_REG_SP, &sp);
+          memset(name, 0, sizeof(char) * 1000);
+          unw_get_proc_name(&cursor, name, sizeof(char) * 1000, &offset);
+          printf("ip = %lx, sp = %lx offset = %lx name = %s\n", (long) ip, (long) sp, (long) offset, name);
+          if (i < names_count)
+            {
+              if (strcmp(names[i], name) != 0)
+                {
+                  test_status = 1;
+                  printf("frame %s doesn't match expected frame %s\n", name, names[i]);
+                }
+              else
+                {
+                  i += 1;
+                }
+            }
+        }
+    }
+
+  if (i != names_count) //Make sure we found all the frames!
+    {
+      printf("Failed to find all frames i:%d != names_count:%d\n", i, names_count);
+      test_status = 1;
+    }
+
+  /*return test_status to test harness*/
+  exit(test_status);
+}
+
+void (*invalid_function)() = (void*)1;
+
+int main(int argc, char *argv[])
+{
+  struct sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  sa.sa_sigaction = handle_sigsegv;
+  sa.sa_flags = SA_SIGINFO;
+  sigaction(SIGSEGV, &sa, NULL);
+
+  invalid_function();
+
+  /*
+   * 99 is the hard error exit status for automake tests:
+   * https://www.gnu.org/software/automake/manual/html_node/Scripts_002dbased-Testsuites.html#Scripts_002dbased-Testsuites
+   * If we dont end up in the signal handler something went horribly wrong.
+   */
+  return 99;
+}