[libc] Implement pkey_alloc/free/get/set/mprotect for x86_64 linux #162362

jtstogel · 2025-10-07T20:06:29Z

This patch provides definitions for pkey_* functions for linux x86_64.

alloc, free, and mprotect are simple syscall wrappers. pkey_set and pkey_get modify architecture-specific registers. The logic for these live in architecture specific directories:

libc/src/sys/mman/linux/x86_64/pkey_common.h has a real implementation
libc/src/sys/mman/linux/generic/pkey_common.h contains stubs that just return ENOSYS.

This is my first addition to LLVM libc. It's likely I've missed something that needs updating -- ample feedback is welcome!

llvmbot · 2025-10-07T20:07:05Z

@llvm/pr-subscribers-libc

Author: Jackson Stogel (jtstogel)

Changes

This patch provides definitions for pkey_* functions for linux x86_64.

alloc, free, and mprotect are simple syscall wrappers. pkey_set and pkey_get modify architecture-specific registers. The logic for these live in architecture specific directories:

libc/src/sys/mman/linux/x86_64/pkey_common.h has a real implementation
libc/src/sys/mman/linux/generic/pkey_common.h contains stubs that just return ENOSYS.

This is my first addition to LLVM libc. It's likely I've missed something that needs updating -- ample feedback is welcome!

Patch is 30.82 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/162362.diff

22 Files Affected:

(modified) libc/config/linux/x86_64/entrypoints.txt (+5)
(modified) libc/src/sys/mman/CMakeLists.txt (+35)
(modified) libc/src/sys/mman/linux/CMakeLists.txt (+75)
(added) libc/src/sys/mman/linux/generic/CMakeLists.txt (+9)
(added) libc/src/sys/mman/linux/generic/pkey_common.h (+25)
(added) libc/src/sys/mman/linux/pkey_alloc.cpp (+37)
(added) libc/src/sys/mman/linux/pkey_free.cpp (+35)
(added) libc/src/sys/mman/linux/pkey_get.cpp (+35)
(added) libc/src/sys/mman/linux/pkey_mprotect.cpp (+45)
(added) libc/src/sys/mman/linux/pkey_set.cpp (+35)
(added) libc/src/sys/mman/linux/x86_64/CMakeLists.txt (+10)
(added) libc/src/sys/mman/linux/x86_64/pkey_common.h (+71)
(added) libc/src/sys/mman/pkey_alloc.h (+20)
(added) libc/src/sys/mman/pkey_free.h (+20)
(added) libc/src/sys/mman/pkey_get.h (+20)
(added) libc/src/sys/mman/pkey_mprotect.h (+21)
(added) libc/src/sys/mman/pkey_set.h (+20)
(modified) libc/test/src/sys/mman/linux/CMakeLists.txt (+21)
(added) libc/test/src/sys/mman/linux/pkey_test.cpp (+241)
(modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+75)
(modified) utils/bazel/llvm-project-overlay/libc/test/UnitTest/BUILD.bazel (+1)
(modified) utils/bazel/llvm-project-overlay/libc/test/src/sys/mman/BUILD.bazel (+18)

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 87b78a337b875..4c56d23d96877 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -264,6 +264,11 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.mman.munlock
     libc.src.sys.mman.munlockall
     libc.src.sys.mman.munmap
+    libc.src.sys.mman.pkey_alloc
+    libc.src.sys.mman.pkey_free
+    libc.src.sys.mman.pkey_get
+    libc.src.sys.mman.pkey_mprotect
+    libc.src.sys.mman.pkey_set
     libc.src.sys.mman.remap_file_pages
     libc.src.sys.mman.posix_madvise
     libc.src.sys.mman.shm_open
diff --git a/libc/src/sys/mman/CMakeLists.txt b/libc/src/sys/mman/CMakeLists.txt
index 4d4c2ad376050..c7be1eddacb5e 100644
--- a/libc/src/sys/mman/CMakeLists.txt
+++ b/libc/src/sys/mman/CMakeLists.txt
@@ -86,6 +86,41 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.msync
 )
 
+add_entrypoint_object(
+  pkey_alloc
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.pkey_alloc
+)
+
+add_entrypoint_object(
+  pkey_free
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.pkey_free
+)
+
+add_entrypoint_object(
+  pkey_get
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.pkey_get
+)
+
+add_entrypoint_object(
+  pkey_mprotect
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.pkey_mprotect
+)
+
+add_entrypoint_object(
+  pkey_set
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.pkey_set
+)
+
 add_entrypoint_object(
   remap_file_pages
   ALIAS
diff --git a/libc/src/sys/mman/linux/CMakeLists.txt b/libc/src/sys/mman/linux/CMakeLists.txt
index 7181bb98a187f..1c79180cbcabb 100644
--- a/libc/src/sys/mman/linux/CMakeLists.txt
+++ b/libc/src/sys/mman/linux/CMakeLists.txt
@@ -1,3 +1,10 @@
+add_subdirectory(generic)
+set(ARCH_SUBDIRECTORY generic)
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
+  add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
+  set(ARCH_SUBDIRECTORY ${LIBC_TARGET_ARCHITECTURE})
+endif()
+
 add_entrypoint_object(
   madvise
   SRCS
@@ -166,6 +173,74 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  pkey_alloc
+  SRCS
+    pkey_alloc.cpp
+  HDRS
+    ../pkey_alloc.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  pkey_free
+  SRCS
+    pkey_free.cpp
+  HDRS
+    ../pkey_free.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  pkey_get
+  SRCS
+    pkey_get.cpp
+  HDRS
+    ../pkey_get.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+    .${ARCH_SUBDIRECTORY}.pkey_common
+)
+
+add_entrypoint_object(
+  pkey_mprotect
+  SRCS
+    pkey_mprotect.cpp
+  HDRS
+    ../pkey_mprotect.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.sys.mman.mprotect
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  pkey_set
+  SRCS
+    pkey_set.cpp
+  HDRS
+    ../pkey_set.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+    .${ARCH_SUBDIRECTORY}.pkey_common
+)
+
 add_entrypoint_object(
   remap_file_pages
   SRCS
diff --git a/libc/src/sys/mman/linux/generic/CMakeLists.txt b/libc/src/sys/mman/linux/generic/CMakeLists.txt
new file mode 100644
index 0000000000000..42b6d96c8387e
--- /dev/null
+++ b/libc/src/sys/mman/linux/generic/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_header_library(
+  pkey_common
+  HDRS
+    pkey_common.h
+  DEPENDS
+    libc.hdr.errno_macros
+    libc.src.__support.common
+    libc.src.__support.error_or
+)
diff --git a/libc/src/sys/mman/linux/generic/pkey_common.h b/libc/src/sys/mman/linux/generic/pkey_common.h
new file mode 100644
index 0000000000000..0811cfb77d4b0
--- /dev/null
+++ b/libc/src/sys/mman/linux/generic/pkey_common.h
@@ -0,0 +1,25 @@
+#ifndef LLVM_SYS_MMAN_LINUX_GENERIC_PKEY_COMMON_H_
+#define LLVM_SYS_MMAN_LINUX_GENERIC_PKEY_COMMON_H_
+
+#include "hdr/errno_macros.h" // For ENOSYS
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace pkey_common {
+
+LIBC_INLINE ErrorOr<int> pkey_get(int pkey) {
+  (void)pkey;
+  return Error(ENOSYS);
+}
+
+LIBC_INLINE ErrorOr<int> pkey_set(int pkey, unsigned int access_rights) {
+  (void)pkey;
+  (void)access_rights;
+  return Error(ENOSYS);
+}
+
+} // namespace pkey_common
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_SYS_MMAN_LINUX_GENERIC_PKEY_COMMON_H_
diff --git a/libc/src/sys/mman/linux/pkey_alloc.cpp b/libc/src/sys/mman/linux/pkey_alloc.cpp
new file mode 100644
index 0000000000000..baf32013bc5c7
--- /dev/null
+++ b/libc/src/sys/mman/linux/pkey_alloc.cpp
@@ -0,0 +1,37 @@
+//===---------- Linux implementation of the Linux pkey_alloc function -----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/pkey_alloc.h"
+
+#include "hdr/errno_macros.h"             // For ENOSYS
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pkey_alloc,
+                   (unsigned int flags, unsigned int access_rights)) {
+#if !defined(SYS_pkey_alloc)
+  libc_errno = ENOSYS;
+  return -1;
+#else
+  int ret =
+      LIBC_NAMESPACE::syscall_impl<int>(SYS_pkey_alloc, flags, access_rights);
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+  return static_cast<int>(ret);
+#endif
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/linux/pkey_free.cpp b/libc/src/sys/mman/linux/pkey_free.cpp
new file mode 100644
index 0000000000000..0228971bd10f6
--- /dev/null
+++ b/libc/src/sys/mman/linux/pkey_free.cpp
@@ -0,0 +1,35 @@
+//===---------- Linux implementation of the Linux pkey_free function ------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/pkey_free.h"
+
+#include "hdr/errno_macros.h"             // For ENOSYS
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pkey_free, (int pkey)) {
+#if !defined(SYS_pkey_free)
+  libc_errno = ENOSYS;
+  return -1;
+#else
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pkey_free, pkey);
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+  return 0;
+#endif
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/linux/pkey_get.cpp b/libc/src/sys/mman/linux/pkey_get.cpp
new file mode 100644
index 0000000000000..623b7930c7a23
--- /dev/null
+++ b/libc/src/sys/mman/linux/pkey_get.cpp
@@ -0,0 +1,35 @@
+//===---------- Linux implementation of the Linux pkey_mprotect function --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/pkey_get.h"
+
+#include "hdr/errno_macros.h" // For ENOSYS
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/architectures.h"
+
+#if defined(LIBC_TARGET_ARCH_IS_X86_64)
+#include "src/sys/mman/linux/x86_64/pkey_common.h"
+#else
+#include "src/sys/mman/linux/generic/pkey_common.h"
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pkey_get, (int pkey)) {
+  ErrorOr<int> ret = LIBC_NAMESPACE::pkey_common::pkey_get(pkey);
+  if (!ret.has_value()) {
+    libc_errno = ret.error();
+    return -1;
+  }
+  return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/linux/pkey_mprotect.cpp b/libc/src/sys/mman/linux/pkey_mprotect.cpp
new file mode 100644
index 0000000000000..15c5d9db39b33
--- /dev/null
+++ b/libc/src/sys/mman/linux/pkey_mprotect.cpp
@@ -0,0 +1,45 @@
+//===---------- Linux implementation of the Linux pkey_mprotect function --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/pkey_mprotect.h"
+
+#include "hdr/errno_macros.h" // For ENOSYS
+#include "hdr/types/size_t.h"
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/sys/mman/mprotect.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pkey_mprotect,
+                   (void *addr, size_t len, int prot, int pkey)) {
+  // Fall back to mprotect if pkey is -1
+  // to maintain compatibility with kernel versions that don't support pkey.
+  if (pkey == -1) {
+    return LIBC_NAMESPACE::mprotect(addr, len, prot);
+  }
+
+#if !defined(SYS_pkey_mprotect)
+  libc_errno = ENOSYS;
+  return -1;
+#else
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pkey_mprotect, addr, len,
+                                              prot, pkey);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+#endif
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/linux/pkey_set.cpp b/libc/src/sys/mman/linux/pkey_set.cpp
new file mode 100644
index 0000000000000..7921443f688d3
--- /dev/null
+++ b/libc/src/sys/mman/linux/pkey_set.cpp
@@ -0,0 +1,35 @@
+//===---------- Linux implementation of the Linux pkey_mprotect function --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/pkey_set.h"
+
+#include "hdr/errno_macros.h" // For ENOSYS
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/config.h"
+
+#if defined(LIBC_TARGET_ARCH_IS_X86_64)
+#include "src/sys/mman/linux/x86_64/pkey_common.h"
+#else
+#include "src/sys/mman/linux/generic/pkey_common.h"
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pkey_set, (int pkey, unsigned int access_rights)) {
+  ErrorOr<int> ret = LIBC_NAMESPACE::pkey_common::pkey_set(pkey, access_rights);
+  if (!ret.has_value()) {
+    libc_errno = ret.error();
+    return -1;
+  }
+  return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/linux/x86_64/CMakeLists.txt b/libc/src/sys/mman/linux/x86_64/CMakeLists.txt
new file mode 100644
index 0000000000000..1ce23af6dbd2a
--- /dev/null
+++ b/libc/src/sys/mman/linux/x86_64/CMakeLists.txt
@@ -0,0 +1,10 @@
+add_header_library(
+  pkey_common
+  HDRS
+    pkey_common.h
+  DEPENDS
+    libc.hdr.errno_macros
+    libc.hdr.stdint_proxy
+    libc.src.__support.common
+    libc.src.__support.error_or
+)
diff --git a/libc/src/sys/mman/linux/x86_64/pkey_common.h b/libc/src/sys/mman/linux/x86_64/pkey_common.h
new file mode 100644
index 0000000000000..bffa9feaed06c
--- /dev/null
+++ b/libc/src/sys/mman/linux/x86_64/pkey_common.h
@@ -0,0 +1,71 @@
+#ifndef LLVM_SYS_MMAN_LINUX_X86_64_PKEY_COMMON_H_
+#define LLVM_SYS_MMAN_LINUX_X86_64_PKEY_COMMON_H_
+
+#include "hdr/errno_macros.h" // For ENOSYS
+#include "hdr/stdint_proxy.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+
+#if !defined(LIBC_TARGET_ARCH_IS_X86_64)
+#error "Invalid include"
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+namespace pkey_common {
+namespace internal {
+
+constexpr int MAX_KEY = 15;
+constexpr int KEY_MASK = 0x3;
+constexpr int BITS_PER_KEY = 2;
+
+// This will SIGILL on CPUs that don't support PKU / OSPKE,
+// but this case should never be reached as a prior pkey_alloc invocation
+// would have failed more gracefully.
+LIBC_INLINE uint32_t read_prku() {
+  uint32_t pkru = 0;
+  uint32_t edx = 0;
+  LIBC_INLINE_ASM("rdpkru" : "=a"(pkru), "=d"(edx) : "c"(0));
+  return pkru;
+}
+
+// This will SIGILL on CPUs that don't support PKU / OSPKE,
+// but this case should never be reached as a prior pkey_alloc invocation
+// would have failed more gracefully.
+LIBC_INLINE void write_prku(uint32_t pkru) {
+  LIBC_INLINE_ASM("wrpkru" : : "a"(pkru), "d"(0), "c"(0));
+}
+
+} // namespace internal
+
+// x86_64 implementation of pkey_get.
+// Returns the access rights for the given pkey on success, errno otherwise.
+LIBC_INLINE ErrorOr<int> pkey_get(int pkey) {
+  if (pkey < 0 || pkey > internal::MAX_KEY) {
+    return Error(EINVAL);
+  }
+
+  uint32_t pkru = internal::read_prku();
+  return (pkru >> (pkey * internal::BITS_PER_KEY)) & internal::KEY_MASK;
+}
+
+// x86_64 implementation of pkey_set.
+// Returns 0 on success, errno otherwise.
+LIBC_INLINE ErrorOr<int> pkey_set(int pkey, unsigned int access_rights) {
+  if (pkey < 0 || pkey > internal::MAX_KEY ||
+      access_rights > internal::KEY_MASK) {
+    return Error(EINVAL);
+  }
+
+  uint32_t pkru = internal::read_prku();
+  pkru &= ~(internal::KEY_MASK << (pkey * internal::BITS_PER_KEY));
+  pkru |=
+      ((access_rights & internal::KEY_MASK) << (pkey * internal::BITS_PER_KEY));
+  internal::write_prku(pkru);
+
+  return 0;
+}
+
+} // namespace pkey_common
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_SYS_MMAN_LINUX_X86_64_PKEY_COMMON_H_
diff --git a/libc/src/sys/mman/pkey_alloc.h b/libc/src/sys/mman/pkey_alloc.h
new file mode 100644
index 0000000000000..c63c6a36c8021
--- /dev/null
+++ b/libc/src/sys/mman/pkey_alloc.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for pkey_alloc function -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_PKEY_ALLOC_H
+#define LLVM_LIBC_SRC_SYS_MMAN_PKEY_ALLOC_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pkey_alloc(unsigned int flags, unsigned int access_rights);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_PKEY_ALLOC_H
diff --git a/libc/src/sys/mman/pkey_free.h b/libc/src/sys/mman/pkey_free.h
new file mode 100644
index 0000000000000..a357e9b8c847b
--- /dev/null
+++ b/libc/src/sys/mman/pkey_free.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for pkey_free function ------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_PKEY_FREE_H
+#define LLVM_LIBC_SRC_SYS_MMAN_PKEY_FREE_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pkey_free(int pkey);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_PKEY_FREE_H
diff --git a/libc/src/sys/mman/pkey_get.h b/libc/src/sys/mman/pkey_get.h
new file mode 100644
index 0000000000000..d41afe08ae371
--- /dev/null
+++ b/libc/src/sys/mman/pkey_get.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for pkey_get function -------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_PKEY_GET_H
+#define LLVM_LIBC_SRC_SYS_MMAN_PKEY_GET_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pkey_get(int pkey);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_PKEY_GET_H
diff --git a/libc/src/sys/mman/pkey_mprotect.h b/libc/src/sys/mman/pkey_mprotect.h
new file mode 100644
index 0000000000000..4d19348ef09db
--- /dev/null
+++ b/libc/src/sys/mman/pkey_mprotect.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for pkey_mprotect function --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_PKEY_MPROTECT_H
+#define LLVM_LIBC_SRC_SYS_MMAN_PKEY_MPROTECT_H
+
+#include "src/__support/macros/config.h"
+#include "hdr/types/size_t.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pkey_mprotect(void *addr, size_t len, int prot, int pkey);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_PKEY_MPROTECT_H
diff --git a/libc/src/sys/mman/pkey_set.h b/libc/src/sys/mman/pkey_set.h
new file mode 100644
index 0000000000000..55bafbd11d709
--- /dev/null
+++ b/libc/src/sys/mman/pkey_set.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for pkey_set function -------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_PKEY_SET_H
+#define LLVM_LIBC_SRC_SYS_MMAN_PKEY_SET_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pkey_set(int pkey, unsigned int access_rights);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_PKEY_SET_H
diff --git a/libc/test/src/sys/mman/linux/CMakeLists.txt b/libc/test/src/sys/mman/linux/CMakeLists.txt
index a362c1cf61cbc..721f89961f7c0 100644
--- a/libc/test/src/sys/mman/linux/CMakeLists.txt
+++ b/libc/test/src/sys/mman/linux/CMakeLists.txt
@@ -67,6 +67,27 @@ add_libc_unittest(
 )
 
 
+add_libc_unittest(
+  pkey_test
+  SUITE
+    libc_sys_mman_unittests
+  SRCS
+    pkey_test.cpp
+  DEPENDS
+    libc.hdr.errno_macros
+    libc.hdr.signal_macros
+    libc.hdr.types.size_t
+    libc.src.sys.mman.mmap
+    libc.src.sys.mman.munmap
+    libc.src.sys.mman.pkey_alloc
+    libc.src.sys.mman.pkey_free
+    libc.src.sys.mman.pkey_get
+    libc.src.sys.mman.pkey_mprotect
+    libc.src.sys.mman.pkey_set
+    libc.test.UnitTest.ErrnoCheckingTest
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
 add_libc_unittest(
   posix_madvise_test
   SUITE
diff --git a/libc/test/src/sys/mman/linux/pkey_test.cpp b/libc/test/src/sys/mman/linux/pkey_test.cpp
new file mode 100644
index 0000000000000..9c6feae2d457b
--- /dev/null
+++ b/libc/test/src/sys/mman/linux/pkey_test.cpp
@@ -0,0 +1,241 @@
+//===-- Unit tests for pkey functions -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
...
[truncated]

github-actions · 2025-10-07T20:09:58Z

✅ With the latest revision this PR passed the C/C++ code formatter.

michaelrj-google

Overall this looks good, but you need to update the headergen file in include/sys/mman.yaml

libc/src/sys/mman/linux/generic/pkey_common.h

libc/src/sys/mman/linux/x86_64/pkey_common.h

SchrodingerZhu · 2025-10-07T20:48:08Z

libc/src/sys/mman/linux/x86_64/pkey_common.h

+LIBC_INLINE uint32_t read_prku() {
+  uint32_t pkru = 0;
+  uint32_t edx = 0;
+  LIBC_INLINE_ASM("rdpkru" : "=a"(pkru), "=d"(edx) : "c"(0));


Are we migrating back to the macro approach for ASM?

I didn't realize there was a preference. Switched to use asm volatile directly.

For setjmp/longjmp we used [[gnu::naked]] so that the whole function was assembly. I'd need to dig up the discussion but I'd say either is probably fine in this case.

libc/src/sys/mman/linux/generic/pkey_common.h

lntue · 2025-10-08T03:03:08Z

libc/src/sys/mman/linux/pkey_mprotect.cpp

+  // Fall back to mprotect if pkey is -1
+  // to maintain compatibility with kernel versions that don't support pkey.
+  if (pkey == -1) {
+    return LIBC_NAMESPACE::mprotect(addr, len, prot);


Can this entrypoint dependency be broken up?

Good catch, thanks. I added a file mprotect_common.h that just exposes the syscall wrapper. WDYT of that vs just duplicating the syscall line?

lntue · 2025-10-08T03:06:51Z

libc/src/sys/mman/linux/x86_64/pkey_common.h

+LIBC_INLINE uint32_t read_prku() {
+  uint32_t pkru = 0;
+  uint32_t edx = 0;
+  asm volatile("rdpkru" : "=a"(pkru), "=d"(edx) : "c"(0));


I think clang has a builtin for this: https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/pkuintrin.h

thanks! switched, much nicer than asm

lntue · 2025-10-08T03:07:25Z

libc/src/sys/mman/linux/x86_64/pkey_common.h

+// but this case should never be reached as a prior pkey_alloc invocation
+// would have failed more gracefully.
+LIBC_INLINE void write_prku(uint32_t pkru) {
+  asm volatile("wrpkru" : : "a"(pkru), "d"(0), "c"(0));


clang probably has builtin for this: https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/pkuintrin.h

lntue · 2025-10-08T03:08:18Z

libc/src/sys/mman/linux/x86_64/pkey_common.h

+  }
+
+  uint32_t pkru = internal::read_prku();
+  return (pkru >> (pkey * internal::BITS_PER_KEY)) & internal::KEY_MASK;


is it possible to overflow on this shift?

it's not possible, since we check bounds on pkey and pkru is always 32 bits

lntue · 2025-10-08T03:08:52Z

libc/src/sys/mman/linux/x86_64/pkey_common.h

+  pkru &= ~(internal::KEY_MASK << (pkey * internal::BITS_PER_KEY));
+  pkru |=
+      ((access_rights & internal::KEY_MASK) << (pkey * internal::BITS_PER_KEY));


similar question about potential overflow here.

likewise should not be possible, since we check bounds on pkey and also mask it against 0x3

libc/test/src/sys/mman/linux/CMakeLists.txt

lntue · 2025-11-04T19:18:38Z

libc/include/sys/mman.yaml

+      - type: int
+  - name: pkey_get
+    standards:
+      - GNUExtensions


lntue · 2025-11-04T19:18:47Z

libc/include/sys/mman.yaml

+      - type: int
+  - name: pkey_set
+    standards:
+      - GNUExtensions


lntue

LGTM with a few nits.

michaelrj-google

Overall design looks good, just a few things I think could be simplified

michaelrj-google · 2025-11-06T22:37:39Z

libc/src/sys/mman/linux/pkey_alloc.cpp

+  libc_errno = ENOSYS;
+  return -1;


generally for syscall wrappers like this we don't bother with the ENOSYS and leave it as a compile time error when building the library.

michaelrj-google · 2025-11-06T22:39:12Z

libc/src/sys/mman/linux/pkey_set.cpp

+#if defined(LIBC_TARGET_ARCH_IS_X86_64)
+#include "src/sys/mman/linux/x86_64/pkey_common.h"
+#else
+#include "src/sys/mman/linux/generic/pkey_common.h"
+#endif


it would make sense to have a top level pkey_common.h so you don't need this logic in multiple files.

michaelrj-google

LGTM

github-actions · 2025-11-18T18:34:18Z

🐧 Linux x64 Test Results

The build succeeded and no tests ran. This is expected in some build configurations.

jtstogel requested review from michaelrj-google and vonosmas October 7, 2025 20:06

jtstogel requested review from aaronmondal, keith and rupprecht as code owners October 7, 2025 20:06

llvmbot added libc bazel "Peripheral" support tier build system: utils/bazel labels Oct 7, 2025

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jtstogel changed the title ~~Implement pkey_alloc/free/get/set/mprotect for x86_64 linux~~ [libc] Implement pkey_alloc/free/get/set/mprotect for x86_64 linux Oct 7, 2025

jtstogel added 4 commits October 7, 2025 21:37

Implement pkey alloc/free/get/set/mprotect for x86_64 linux

6eb5a45

Add pkey_* to generated sys/mman.h. Fix formatting.

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Add license headers.

50f264e

Prefer direct use of 'asm volatile' over LIBC_INLINE_ASM.

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jtstogel force-pushed the add-pkey-x86 branch from bce9ae9 to e67b0c5 Compare October 7, 2025 21:38

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jtstogel added 4 commits November 3, 2025 20:36

Use instrinsics instead of asm. Don't depend on mprotect entrypoint.

30b1d22

Merge branch 'main' into add-pkey-x86

c1f6650

Remove dependency on mprotect entrypoint from pkey_mprotect.

1780027

Format files.

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jtstogel requested a review from lntue November 3, 2025 20:58

lntue reviewed Nov 4, 2025

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libc/include/sys/mman.yaml Outdated

- type: int

- name: pkey_get

standards:

- GNUExtensions

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nit: gnu

lntue reviewed Nov 4, 2025

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libc/include/sys/mman.yaml Outdated

- type: int

- name: pkey_set

standards:

- GNUExtensions

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nit: gnu

lntue approved these changes Nov 4, 2025

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jtstogel added 2 commits November 6, 2025 20:25

Fix standard specification in mman.yaml

75b4ab6

Merge branch 'main' into add-pkey-x86

45324d7

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jtstogel added 2 commits November 10, 2025 22:08

Disable sanitizers for pkey_test.

b37cb4b

Deduplicate logic for picking architecture-specific pkey_common.h.

2211955

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Merge branch 'main' into add-pkey-x86

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jtstogel added 2 commits November 18, 2025 19:23

Fix select condition in BUILD.bazel

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Merge branch 'main' into add-pkey-x86

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jtstogel merged commit db71cc5 into llvm:main Nov 18, 2025
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[libc] Implement pkey_alloc/free/get/set/mprotect for x86_64 linux #162362

[libc] Implement pkey_alloc/free/get/set/mprotect for x86_64 linux #162362

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