Merge pull request #5097 from wcampbell-nv/cmdline-map

Remap /proc/pid/cmdline with PR_SET_MM_MAP

Source/Tools/CommonTools/CodeLoader.h

@@ -54,17 +54,6 @@ public:
     return ApplicationArgs;
   }
 
-  /**
-   * Writes out the arguments in the format of /proc/self/cmdline
-   */
-  virtual void WriteCmdlineFD(int32_t fd) const {
-    const auto& Args = GetApplicationArguments();
-    // cmdline is an array of null terminated arguments
-    for (const auto& Arg : Args) {
-      write(fd, Arg.c_str(), Arg.size() + 1); // Add 1 to include the null terminator
-    }
-  }
-
 protected:
   fextl::vector<fextl::string> ApplicationArgs;
 };

Source/Tools/FEXInterpreter/ELFCodeLoader.h

@@ -17,6 +17,7 @@
 #include <FEXCore/Core/X86Enums.h>
 #include <FEXCore/Utils/LogManager.h>
 #include <FEXCore/Utils/TypeDefines.h>
+#include <FEXCore/Utils/FileLoading.h>
 #include <FEXCore/fextl/list.h>
 #include <FEXCore/fextl/string.h>
 #include <FEXCore/fextl/vector.h>
@@ -29,7 +30,9 @@
 #include <sys/auxv.h>
 #include <sys/mman.h>
 #include <sys/personality.h>
+#include <sys/prctl.h>
 #include <sys/random.h>
+#include <linux/prctl.h>
 
 #define PAGE_START(x) ((x) & ~(uintptr_t)(4095))
 #define PAGE_OFFSET(x) ((x) & 4095)
@@ -707,6 +710,63 @@ public:
     *AuxTabSize = sizeof(AuxType) * AuxVariables.size();
   }
 
+  // Get the current memory map from /proc/self/stat
+  static bool GetCurrentMap(struct prctl_mm_map& map) {
+
+    // /proc/self/stat has 52 fields of at most 20 digits each (UINT64_MAX).
+    // 52*20 = 1040, so 2048 is a conservative upper bound
+    char stat_buffer[2048];
+    ssize_t bytes_read = FEXCore::FileLoading::LoadFileToBuffer("/proc/self/stat", stat_buffer);
+
+    // Ensure we don't read past the end into garbage data
+    stat_buffer[std::clamp(bytes_read, 0L, static_cast<ssize_t>(sizeof(stat_buffer)) - 1)] = '\0';
+
+    // See man proc_pid_stat
+    int items_read = sscanf(stat_buffer,
+                            "%*d %*s %*c %*d %*d "      // 1 to 5
+                            "%*d %*d %*d %*u %*u "      // 6 to 10
+                            "%*u %*u %*u %*u %*u "      // 11 to 15
+                            "%*d %*d %*d %*d %*d "      // 16 to 20
+                            "%*d %*u %*u %*d %*u "      // 21 to 25
+                            "%llu %llu %llu %*u %*u "   // 26 to 30
+                            "%*u %*u %*u %*u %*u "      // 31 to 35
+                            "%*u %*u %*d %*d %*u "      // 36 to 40
+                            "%*u %*u %*u %*d %llu "     // 40 to 45
+                            "%llu %llu %llu %llu %llu " // 46 to 50
+                            "%llu",                     // 51
+                            &map.start_code, &map.end_code, &map.start_stack, &map.start_data, &map.end_data, &map.start_brk,
+                            &map.arg_start, &map.arg_end, &map.env_start, &map.env_end);
+
+    if (items_read != 10) {
+      return false;
+    }
+
+    map.brk = reinterpret_cast<uint64_t>(sbrk(0));
+
+    // The kernel will leave these values unchanged, see implementation in sys.c
+    map.auxv = NULL;
+    map.auxv_size = 0;
+    map.exe_fd = -1;
+
+    return true;
+  }
+
+  // Point the OS to our new stack's argument data
+  void RemapArgumentData(uintptr_t NewArgStart, uint64_t ArgSize) {
+    struct prctl_mm_map map {};
+    if (GetCurrentMap(map)) {
+      map.arg_start = NewArgStart;
+      map.arg_end = NewArgStart + ArgSize;
+
+      int r = prctl(PR_SET_MM, PR_SET_MM_MAP, &map, sizeof(map), 0L);
+      if (r != 0) {
+        LogMan::Msg::EFmt("Failed to remap /proc/pid/cmdline data (prctl failed: result {}, errno {})", r, errno);
+      }
+    } else {
+      LogMan::Msg::EFmt("Failed to remap /proc/pid/cmdline data (GetCurrentMap failed)");
+    }
+  }
+
   // Setups the stack initial data (argv, envp, auxv)
   void SetupStack() {
     StackPointer += StackSize();
@@ -803,6 +863,8 @@ public:
       SetupPointers<uint32_t, auxv32_t, 4>(StackPointer, AuxVOffset, ArgumentOffset, EnvpOffset, ApplicationArgs, EnvironmentVariables,
                                            AuxVariables, &AuxTabBase, &AuxTabSize);
     }
+
+    RemapArgumentData(StackPointer + ArgumentOffset, ArgumentBackingSize);
   }
 
   fextl::vector<const char*> GetExecveArguments() const override {
@@ -816,15 +878,6 @@ public:
     };
   }
 
-  void WriteCmdlineFD(int32_t fd) const override {
-    // '/proc/self/cmdline' typically maps to the stack's argv data.
-    // Applications can write to this to change the cmdline value,
-    // but in FEX they'll write to the emulated stack rather than the OS'.
-    //
-    // Expose the contents of the emulated stack's argument data.
-    write(fd, reinterpret_cast<const void*>(StackPointer + ArgumentOffset), ArgumentBackingSize);
-  }
-
   uint64_t GetBaseOffset() const override {
     return BaseOffset;
   }

Source/Tools/LinuxEmulation/LinuxSyscalls/EmulatedFiles/EmulatedFiles.cpp

@@ -586,21 +586,6 @@ EmulatedFDManager::EmulatedFDManager(FEXCore::Context::Context* ctx)
   FDReadCreators[procAuxv] = &EmulatedFDManager::ProcAuxv;
   FDReadCreators["/proc/self/auxv"] = &EmulatedFDManager::ProcAuxv;
 
-  auto cmdline_handler = [&](FEXCore::Context::Context* ctx, int32_t fd, const char* pathname, int32_t flags, mode_t mode) -> int32_t {
-    const int FD = GenTmpFD(pathname, flags);
-    const auto* CodeLoader = FEX::HLE::_SyscallHandler->GetCodeLoader();
-    CodeLoader->WriteCmdlineFD(FD);
-
-    // One additional null terminator to finish the list
-    lseek(FD, 0, SEEK_SET);
-    SealTmpFD(FD);
-    return FD;
-  };
-
-  FDReadCreators["/proc/self/cmdline"] = cmdline_handler;
-  fextl::string procCmdLine = fextl::fmt::format("/proc/{}/cmdline", getpid());
-  FDReadCreators[procCmdLine] = cmdline_handler;
-
   if (ThreadsConfig > 1) {
     cpus_online = fextl::fmt::format("0-{}", ThreadsConfig - 1);
   } else {