From 2b053b1c28bd1df6475ae133766db2f52dd564e8 Mon Sep 17 00:00:00 2001 From: Kostya Kortchinsky Date: Wed, 21 Jun 2017 15:56:03 +0000 Subject: [sanitizer] Add a function to gather random bytes Summary: AFAICT compiler-rt doesn't have a function that would return 'good' random bytes to seed a PRNG. Currently, the `SizeClassAllocator64` uses addresses returned by `mmap` to seed its PRNG, which is not ideal, and `SizeClassAllocator32` doesn't benefit from the entropy offered by its 64-bit counterpart address space, so right now it has nothing. This function aims at solving this, allowing to implement good 32-bit chunk randomization. Scudo also has a function that does this for Cookie purposes, which would go away in a later CL once this lands. This function will try the `getrandom` syscall if available, and fallback to `/dev/urandom` if not. Unfortunately, I do not have a way to implement and test a Mac and Windows version, so those are unimplemented as of now. Note that `kRandomShuffleChunks` is only used on Linux for now. Reviewers: alekseyshl Reviewed By: alekseyshl Subscribers: zturner, rnk, llvm-commits, kubamracek Differential Revision: https://reviews.llvm.org/D34412 llvm-svn: 305922 --- .../lib/sanitizer_common/sanitizer_linux.cc | 26 ++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'compiler-rt/lib/sanitizer_common/sanitizer_linux.cc') diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc index d31c49d694a..a94a63c7f16 100644 --- a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc +++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc @@ -1604,6 +1604,32 @@ uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding) { return 0; } +bool GetRandom(void *buffer, uptr length) { + if (!buffer || !length || length > 256) + return false; +#if defined(__NR_getrandom) + static atomic_uint8_t skip_getrandom_syscall; + if (!atomic_load_relaxed(&skip_getrandom_syscall)) { + // Up to 256 bytes, getrandom will not be interrupted. + uptr res = internal_syscall(SYSCALL(getrandom), buffer, length, 0); + int rverrno = 0; + if (internal_iserror(res, &rverrno) && rverrno == ENOSYS) + atomic_store_relaxed(&skip_getrandom_syscall, 1); + else if (res == length) + return true; + } +#endif + uptr fd = internal_open("/dev/urandom", O_RDONLY); + if (internal_iserror(fd)) + return false; + // internal_read deals with EINTR. + uptr res = internal_read(fd, buffer, length); + if (internal_iserror(res)) + return false; + internal_close(fd); + return true; +} + } // namespace __sanitizer #endif // SANITIZER_FREEBSD || SANITIZER_LINUX -- cgit v1.2.3