[libc] [llvm] [libc] Implement pkey_alloc/free/get/set/mprotect for x86_64 linux (PR #162362)

[Jackson Stogel via llvm-commits]

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@@ -0,0 +1,79 @@
+//===---------- x86_64-specific implementations for pkey_{get,set}. -------===//
+//
+// 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_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;
+  asm volatile("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) {
+  asm volatile("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;
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jtstogel wrote:

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

https://github.com/llvm/llvm-project/pull/162362