RFC: Add tests for some CHERI-specific behaviors

Author: nwf-msr

src/test/func/cheri/cheri.cc

@@ -0,0 +1,153 @@
+#include <iostream>
+
+#if defined(SNMALLOC_PASS_THROUGH) || !defined(__CHERI_PURE_CAPABILITY__)
+// This test does not make sense in pass-through or w/o CHERI
+int main()
+{
+  return 0;
+}
+#else
+
+// #  define SNMALLOC_TRACING
+
+#  include <cheri/cherireg.h>
+#  include <snmalloc/snmalloc.h>
+#  include <stddef.h>
+
+#  if defined(__FreeBSD__)
+#    include <sys/mman.h>
+#  endif
+
+using namespace snmalloc;
+
+bool cap_len_is(void* cap, size_t expected)
+{
+  return __builtin_cheri_length_get(cap) == expected;
+}
+
+bool cap_vmem_perm_is(void* cap, bool expected)
+{
+#  if defined(CHERI_PERM_SW_VMEM)
+  return !!(__builtin_cheri_perms_get(cap) & CHERI_PERM_SW_VMEM) == expected;
+#  else
+#    warning "Don't know how to check VMEM permission bit"
+#  endif
+}
+
+int main()
+{
+
+#  if defined(__FreeBSD__)
+  {
+    size_t pagesize[8];
+    int err = getpagesizes(pagesize, sizeof(pagesize) / sizeof(pagesize[0]));
+    SNMALLOC_CHECK(err > 0);
+    SNMALLOC_CHECK(pagesize[0] == OS_PAGE_SIZE);
+  }
+#  endif
+
+  auto alloc = get_scoped_allocator();
+
+  message("Grab small object");
+  {
+    static const size_t sz = 128;
+    void* o1 = alloc->alloc(sz);
+    SNMALLOC_CHECK(cap_len_is(o1, sz));
+    SNMALLOC_CHECK(cap_vmem_perm_is(o1, false));
+    alloc->dealloc(o1);
+  }
+
+  /*
+   * This large object is sized to end up in our alloc's local buddy allocators
+   * when it's released.
+   */
+  message("Grab large object");
+  ptraddr_t alarge;
+  {
+    static const size_t sz = 1024 * 1024;
+    void* olarge = alloc->alloc(sz);
+    alarge = address_cast(olarge);
+    SNMALLOC_CHECK(cap_len_is(olarge, sz));
+    SNMALLOC_CHECK(cap_vmem_perm_is(olarge, false));
+
+    static_cast<uint8_t*>(olarge)[128] = 'x';
+    static_cast<uint8_t*>(olarge)[128 + OS_PAGE_SIZE] = 'y';
+
+#  if defined(__FreeBSD__)
+    static constexpr int irm =
+      MINCORE_INCORE | MINCORE_REFERENCED | MINCORE_MODIFIED;
+    char ic[2];
+    int err = mincore(olarge, 2 * OS_PAGE_SIZE, ic);
+    SNMALLOC_CHECK(err == 0);
+    SNMALLOC_CHECK((ic[0] & irm) == irm);
+    SNMALLOC_CHECK((ic[1] & irm) == irm);
+    message("Large object in core; good");
+#  endif
+
+    alloc->dealloc(olarge);
+  }
+
+  message("Grab large object again, verify reuse");
+  {
+    static const size_t sz = 1024 * 1024;
+    errno = 0;
+    void* olarge = alloc->alloc<YesZero>(sz);
+    int err = errno;
+
+    SNMALLOC_CHECK(alarge == address_cast(olarge));
+    SNMALLOC_CHECK(err == 0);
+
+#  if defined(__FreeBSD__)
+    /*
+     * Verify that the zeroing took place by mmap, which should mean that the
+     * first two pages are not in core.  This implies that snmalloc successfully
+     * re-derived a Chunk- or Arena-bounded pointer and used that, and its VMAP
+     * permission, to tear pages out of the address space.
+     */
+    static constexpr int irm =
+      MINCORE_INCORE | MINCORE_REFERENCED | MINCORE_MODIFIED;
+    char ic[2];
+    err = mincore(olarge, 2 * OS_PAGE_SIZE, ic);
+    SNMALLOC_CHECK(err == 0);
+    SNMALLOC_CHECK((ic[0] & irm) == 0);
+    SNMALLOC_CHECK((ic[1] & irm) == 0);
+    message("Large object not in core; good");
+#  endif
+
+    SNMALLOC_CHECK(static_cast<uint8_t*>(olarge)[128] == '\0');
+    SNMALLOC_CHECK(static_cast<uint8_t*>(olarge)[128 + OS_PAGE_SIZE] == '\0');
+    SNMALLOC_CHECK(cap_len_is(olarge, sz));
+    SNMALLOC_CHECK(cap_vmem_perm_is(olarge, false));
+
+    alloc->dealloc(olarge);
+  }
+
+  /*
+   * Grab another CoreAlloc pointer from the pool and examine it.
+   *
+   * CoreAlloc-s come from the metadata pools of snmalloc, and so do not flow
+   * through the usual allocation machinery.
+   */
+  message("Grab CoreAlloc from pool for inspection");
+  {
+    static_assert(
+      std::is_same_v<decltype(alloc.alloc), LocalAllocator<StandardConfig>>);
+
+    LocalCache lc{&StandardConfig::unused_remote};
+    auto* ca = AllocPool<StandardConfig>::acquire(&lc);
+
+    SNMALLOC_CHECK(cap_len_is(ca, sizeof(*ca)));
+    SNMALLOC_CHECK(cap_vmem_perm_is(ca, false));
+
+    /*
+     * Putting ca back into the pool would require unhooking our local cache,
+     * and that requires accessing privates.  Since it's pretty harmless to do
+     * so here at the end of our test, just leak it.
+     */
+  }
+
+  message("CHERI checks OK");
+  return 0;
+}
+
+#endif