Merge bitcoin/bitcoin#27699: random: drop syscall wrapper usage for getrandom()

5228223 ci: remove MSAN getrandom syscall workaround (fanquake)
d5e0691 random: switch to using getrandom() directly (fanquake)
c2ba3f5 random: add [[maybe_unused]] to GetDevURandom (fanquake)
c13c97d random: getentropy on macOS does not need unistd.h (fanquake)

Pull request description:

  This requires a linux kernel of `3.17`+, which seems entirely
  reasonable. `3.17` went EOL in 2015, and the last supported `3.x` kernel
  (`3.16`) went EOL > 4 years ago, in 2020. For reference, the current
  oldest maintained kernel is `4.14` (released 2017, going EOL Jan 2024).

  Support for `getrandom()` (and `getentropy()`) was added to
  glibc `2.25` https://sourceware.org/legacy-ml/libc-alpha/2017-02/msg00079.html:
  > * The getentropy and getrandom functions, and the <sys/random.h> header
    file have been added.

  and we already require `2.27` or later.

  All that being said, I don't think you would encounter a current day (+~6 months from now)
  system, running with kernel headers older than 3.17 (released 2014) but also having a
  glibc of 2.27+ (released 2018)?

  Removing this (our only) use of `syscall()` also means we can drop a workaround in our MSAN jobs.
  If this is merged, I'll drop the [same workaround in oss-fuzz](https://github.com/google/oss-fuzz/blob/25946a544856413d31d9cbb3a366a4aef5a8fd60/projects/bitcoin-core/build.sh#L49-L56).

ACKs for top commit:
  josibake:
    ACK bitcoin/bitcoin@5228223
  hebasto:
    ACK 5228223, I've tested build system changes on Ubuntu 22.04 and macOS Monterey 12.6.6 (x86_64).

Tree-SHA512: cc978e08510c461b875ca8c08ae176b4519fa1108f0efd74dcb7474518945357e0184e54423282c9a496de195e4ddc3e221ee78623bd63e24c50cc86acdf32e2

Author: fanquake

ci/test/06_script_b.sh

@@ -101,14 +101,6 @@ cd "${BASE_BUILD_DIR}/bitcoin-$HOST"
 
 bash -c "./configure --cache-file=../config.cache $BITCOIN_CONFIG_ALL $BITCOIN_CONFIG" || ( (cat config.log) && false)
 
-if [[ ${USE_MEMORY_SANITIZER} == "true" ]]; then
-  # MemorySanitizer (MSAN) does not support tracking memory initialization done by
-  # using the Linux getrandom syscall. Avoid using getrandom by undefining
-  # HAVE_SYS_GETRANDOM. See https://github.com/google/sanitizers/issues/852 for
-  # details.
-  grep -v HAVE_SYS_GETRANDOM src/config/bitcoin-config.h > src/config/bitcoin-config.h.tmp && mv src/config/bitcoin-config.h.tmp src/config/bitcoin-config.h
-fi
-
 if [[ "${RUN_TIDY}" == "true" ]]; then
   MAYBE_BEAR="bear --config src/.bear-tidy-config"
   MAYBE_TOKEN="--"

configure.ac

@@ -1170,17 +1170,16 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <ctime>]],
 )
 
 dnl Check for different ways of gathering OS randomness
-AC_MSG_CHECKING([for Linux getrandom syscall])
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
-  #include <sys/syscall.h>
-  #include <linux/random.h>]],
- [[ syscall(SYS_getrandom, nullptr, 32, 0); ]])],
- [ AC_MSG_RESULT([yes]); AC_DEFINE([HAVE_SYS_GETRANDOM], [1], [Define this symbol if the Linux getrandom system call is available]) ],
+AC_MSG_CHECKING([for Linux getrandom function])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+  #include <sys/random.h>]],
+ [[ getrandom(nullptr, 32, 0); ]])],
+ [ AC_MSG_RESULT([yes]); AC_DEFINE([HAVE_GETRANDOM], [1], [Define this symbol if the Linux getrandom function call is available]) ],
  [ AC_MSG_RESULT([no])]
 )
 
-AC_MSG_CHECKING([for getentropy via random.h])
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
+AC_MSG_CHECKING([for getentropy via sys/random.h])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
  #include <sys/random.h>]],
  [[ getentropy(nullptr, 32) ]])],
  [ AC_MSG_RESULT([yes]); AC_DEFINE([HAVE_GETENTROPY_RAND], [1], [Define this symbol if the BSD getentropy system call is available with sys/random.h]) ],

doc/dependencies.md

@@ -20,7 +20,7 @@ You can find installation instructions in the `build-*.md` file for your platfor
 | [Boost](../depends/packages/boost.mk) | [link](https://www.boost.org/users/download/) | [1.81.0](https://github.com/bitcoin/bitcoin/pull/26557) | [1.64.0](https://github.com/bitcoin/bitcoin/pull/22320) | No |
 | [libevent](../depends/packages/libevent.mk) | [link](https://github.com/libevent/libevent/releases) | [2.1.12-stable](https://github.com/bitcoin/bitcoin/pull/21991) | [2.1.8](https://github.com/bitcoin/bitcoin/pull/24681) | No |
 | glibc | [link](https://www.gnu.org/software/libc/) | N/A | [2.27](https://github.com/bitcoin/bitcoin/pull/27029) | Yes |
-| Linux Kernel | [link](https://www.kernel.org/) | N/A | 3.2.0 | Yes |
+| Linux Kernel | [link](https://www.kernel.org/) | N/A | [3.17.0](https://github.com/bitcoin/bitcoin/pull/27699) | Yes |
 
 ## Optional
 

src/random.cpp

@@ -28,14 +28,10 @@
 #include <sys/time.h>
 #endif
 
-#ifdef HAVE_SYS_GETRANDOM
-#include <sys/syscall.h>
-#include <linux/random.h>
-#endif
-#if defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
-#include <unistd.h>
+#if defined(HAVE_GETRANDOM) || (defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX))
 #include <sys/random.h>
 #endif
+
 #ifdef HAVE_SYSCTL_ARND
 #include <sys/sysctl.h>
 #endif
@@ -252,7 +248,7 @@ static void Strengthen(const unsigned char (&seed)[32], SteadyClock::duration du
 /** Fallback: get 32 bytes of system entropy from /dev/urandom. The most
  * compatible way to get cryptographic randomness on UNIX-ish platforms.
  */
-static void GetDevURandom(unsigned char *ent32)
+[[maybe_unused]] static void GetDevURandom(unsigned char *ent32)
 {
     int f = open("/dev/urandom", O_RDONLY);
     if (f == -1) {
@@ -285,23 +281,14 @@ void GetOSRand(unsigned char *ent32)
         RandFailure();
     }
     CryptReleaseContext(hProvider, 0);
-#elif defined(HAVE_SYS_GETRANDOM)
+#elif defined(HAVE_GETRANDOM)
     /* Linux. From the getrandom(2) man page:
      * "If the urandom source has been initialized, reads of up to 256 bytes
      * will always return as many bytes as requested and will not be
      * interrupted by signals."
      */
-    int rv = syscall(SYS_getrandom, ent32, NUM_OS_RANDOM_BYTES, 0);
-    if (rv != NUM_OS_RANDOM_BYTES) {
-        if (rv < 0 && errno == ENOSYS) {
-            /* Fallback for kernel <3.17: the return value will be -1 and errno
-             * ENOSYS if the syscall is not available, in that case fall back
-             * to /dev/urandom.
-             */
-            GetDevURandom(ent32);
-        } else {
-            RandFailure();
-        }
+    if (getrandom(ent32, NUM_OS_RANDOM_BYTES, 0) != NUM_OS_RANDOM_BYTES) {
+        RandFailure();
     }
 #elif defined(__OpenBSD__)
     /* OpenBSD. From the arc4random(3) man page:
@@ -311,16 +298,10 @@ void GetOSRand(unsigned char *ent32)
        The function call is always successful.
      */
     arc4random_buf(ent32, NUM_OS_RANDOM_BYTES);
-    // Silence a compiler warning about unused function.
-    (void)GetDevURandom;
 #elif defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
-    /* getentropy() is available on macOS 10.12 and later.
-     */
     if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
         RandFailure();
     }
-    // Silence a compiler warning about unused function.
-    (void)GetDevURandom;
 #elif defined(HAVE_SYSCTL_ARND)
     /* FreeBSD, NetBSD and similar. It is possible for the call to return less
      * bytes than requested, so need to read in a loop.
@@ -334,8 +315,6 @@ void GetOSRand(unsigned char *ent32)
         }
         have += len;
     } while (have < NUM_OS_RANDOM_BYTES);
-    // Silence a compiler warning about unused function.
-    (void)GetDevURandom;
 #else
     /* Fall back to /dev/urandom if there is no specific method implemented to
      * get system entropy for this OS.