Kernel+LibC+LibELF: Set stack size based on PT_GNU_STACK during execve

Some programs explicitly ask for a different initial stack size than
what the OS provides. This is implemented in ELF by having a
PT_GNU_STACK header which has its p_memsz set to the amount that the
program requires. This commit implements this policy by reading the
p_memsz of the header and setting the main thread stack size to that.
ELF::Image::validate_program_headers ensures that the size attribute is
a reasonable value.

Kernel/API/POSIX/sys/limits.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, sin-ack <sin-ack@protonmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -7,3 +8,5 @@
 #pragma once
 
 #define NGROUPS_MAX 32
+
+#define PTHREAD_STACK_MIN (64 * 1024) // 64KiB

Kernel/API/Syscall.h

@@ -360,7 +360,7 @@ struct SC_create_thread_params {
     // ... ok, if you say so posix. Guess we get to lie to people about guard page size
     unsigned int guard_page_size = 0;          // Rounded up to PAGE_SIZE
     unsigned int reported_guard_page_size = 0; // The lie we tell callers
-    unsigned int stack_size = 1 * MiB;         // Default PTHREAD_STACK_MIN
+    unsigned int stack_size = 1 * MiB;         // Equal to Thread::default_userspace_stack_size
     void* stack_location;                      // nullptr means any, o.w. process virtual address
 #    if ARCH(X86_64)
     FlatPtr rdi;

Kernel/API/serenity_limits.h

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2022, sin-ack <sin-ack@protonmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#define PTHREAD_STACK_MAX (8 * 1024 * 1024) // 8MiB

Kernel/Syscalls/execve.cpp

@@ -279,6 +279,7 @@ static ErrorOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace> n
     size_t master_tls_size = 0;
     size_t master_tls_alignment = 0;
     FlatPtr load_base_address = 0;
+    size_t stack_size = 0;
 
     auto elf_name = TRY(object_description.pseudo_path());
     VERIFY(!Processor::in_critical());
@@ -374,6 +375,10 @@ static ErrorOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace> n
         if (program_header.type() == PT_LOAD)
             return load_section(program_header);
 
+        if (program_header.type() == PT_GNU_STACK) {
+            stack_size = program_header.size_in_memory();
+        }
+
         // NOTE: We ignore other program header types.
         return {};
     };
@@ -387,12 +392,16 @@ static ErrorOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace> n
         return result;
     }());
 
+    if (stack_size == 0) {
+        stack_size = Thread::default_userspace_stack_size;
+    }
+
     if (!elf_image.entry().offset(load_offset).get()) {
         dbgln("do_exec: Failure loading program, entry pointer is invalid! {})", elf_image.entry().offset(load_offset));
         return ENOEXEC;
     }
 
-    auto* stack_region = TRY(new_space->allocate_region(Memory::RandomizeVirtualAddress::Yes, {}, Thread::default_userspace_stack_size, PAGE_SIZE, "Stack (Main thread)"sv, PROT_READ | PROT_WRITE, AllocationStrategy::Reserve));
+    auto* stack_region = TRY(new_space->allocate_region(Memory::RandomizeVirtualAddress::Yes, {}, stack_size, PAGE_SIZE, "Stack (Main thread)"sv, PROT_READ | PROT_WRITE, AllocationStrategy::Reserve));
     stack_region->set_stack(true);
 
     return LoadResult {

Userland/Libraries/LibC/elf.h

@@ -487,7 +487,7 @@ typedef struct {
 
 #define PT_GNU_EH_FRAME 0x6474e550 /* Exception handling info */
 #define PT_GNU_RELRO 0x6474e552    /* Read-only after relocation */
-#define PT_GNU_STACK 0x6474e551    /* Stack permissions info */
+#define PT_GNU_STACK 0x6474e551    /* Stack permissions & size info */
 
 #define PT_OPENBSD_RANDOMIZE 0x65a3dbe6 /* fill with random data */
 #define PT_OPENBSD_WXNEEDED 0x65a3dbe7  /* program performs W^X violations */

Userland/Libraries/LibC/limits.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <Kernel/API/POSIX/sys/limits.h>
+#include <Kernel/API/serenity_limits.h>
 #include <bits/posix1_lim.h>
 #include <bits/stdint.h>
 #include <bits/wchar.h>
@@ -86,8 +87,6 @@
 
 #define ARG_MAX 65536
 
-#define PTHREAD_STACK_MIN 65536
-
 #define SSIZE_MAX 2147483647
 
 #define LINK_MAX 4096

Userland/Libraries/LibC/pthread.cpp

@@ -34,7 +34,6 @@ using PthreadAttrImpl = Syscall::SC_create_thread_params;
 
 static constexpr size_t required_stack_alignment = 4 * MiB;
 static constexpr size_t highest_reasonable_guard_size = 32 * PAGE_SIZE;
-static constexpr size_t highest_reasonable_stack_size = 8 * MiB; // That's the default in Ubuntu?
 
 __thread void* s_stack_location;
 __thread size_t s_stack_size;
@@ -467,7 +466,7 @@ int pthread_attr_setstacksize(pthread_attr_t* attributes, size_t stack_size)
     if (!attributes_impl)
         return EINVAL;
 
-    if ((stack_size < PTHREAD_STACK_MIN) || stack_size > highest_reasonable_stack_size)
+    if (stack_size < PTHREAD_STACK_MIN || stack_size > PTHREAD_STACK_MAX)
         return EINVAL;
 
     attributes_impl->stack_size = stack_size;

Userland/Libraries/LibELF/Image.cpp

@@ -12,6 +12,7 @@
 #include <AK/QuickSort.h>
 #include <AK/StringBuilder.h>
 #include <AK/StringView.h>
+#include <Kernel/API/serenity_limits.h>
 #include <LibELF/Image.h>
 #include <LibELF/Validation.h>
 #include <limits.h>

Userland/Libraries/LibELF/Validation.cpp

@@ -7,6 +7,7 @@
 
 #include <AK/Assertions.h>
 #include <AK/Checked.h>
+#include <Kernel/API/serenity_limits.h>
 #include <LibC/elf.h>
 #include <LibELF/Validation.h>
 #include <limits.h>
@@ -298,6 +299,21 @@ ErrorOr<bool> validate_program_headers(ElfW(Ehdr) const& elf_header, size_t file
                 if (verbose)
                     dbgln("Possible shenanigans! Validating an ELF with executable stack.");
             }
+
+            if (program_header.p_memsz != 0) {
+                if (program_header.p_memsz < static_cast<unsigned>(PTHREAD_STACK_MIN) || program_header.p_memsz > static_cast<unsigned>(PTHREAD_STACK_MAX)) {
+                    if (verbose)
+                        dbgln("PT_GNU_STACK defines an unacceptable stack size.");
+                    return false;
+                }
+
+                if (program_header.p_memsz % PAGE_SIZE != 0) {
+                    if (verbose)
+                        dbgln("PT_GNU_STACK size is not page-aligned.");
+                    return false;
+                }
+            }
+
             break;
         case PT_GNU_RELRO:
             if ((program_header.p_flags & PF_X) && (program_header.p_flags & PF_W)) {