tests: add tcg coverage for fixed mremap bugs

These tests cover the first two fixes in this patch series. The final
patch is not covered because the bug it fixes is not easily observable
by the guest.

Signed-off-by: Matthew Lugg <mlugg@mlugg.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20251117170954.31451-5-mlugg@mlugg.co.uk>

tests/tcg/multiarch/test-mmap.c

@@ -22,6 +22,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
@@ -41,7 +42,7 @@ do                                                             \
   }                                                            \
 } while (0)
 
-unsigned char *dummybuf;
+unsigned char *dummybuf; /* length is 2*pagesize */
 static unsigned int pagesize;
 static unsigned int pagemask;
 int test_fd;
@@ -451,9 +452,45 @@ void check_invalid_mmaps(void)
     fail_unless(addr == MAP_FAILED);
     fail_unless(errno == ENOMEM);
 
+    /* Attempt to remap a region which exceeds the bounds of memory. */
+    addr = mremap((void *)((uintptr_t)pagesize * 10), SIZE_MAX & ~(size_t)pagemask, pagesize, 0);
+    fprintf(stdout, "%s mremap addr=%p", __func__, (void *)addr);
+    fail_unless(addr == MAP_FAILED);
+    fail_unless(errno == EFAULT);
+
     fprintf(stdout, " passed\n");
 }
 
+void check_shrink_mmaps(void)
+{
+    unsigned char *a, *b, *c;
+    a = mmap(NULL, pagesize * 2, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    b = mmap(NULL, pagesize * 2, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    c = mmap(NULL, pagesize * 2, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+    fail_unless(a != MAP_FAILED);
+    fail_unless(b != MAP_FAILED);
+    fail_unless(c != MAP_FAILED);
+
+    /* Ensure we can read the full mappings */
+    memcpy(dummybuf, a, 2 * pagesize);
+    memcpy(dummybuf, b, 2 * pagesize);
+    memcpy(dummybuf, c, 2 * pagesize);
+
+    /* Shrink the middle mapping in-place; the others should be unaffected */
+    b = mremap(b, pagesize * 2, pagesize, 0);
+    fail_unless(b != MAP_FAILED);
+
+    /* Ensure we can still access all valid mappings */
+    memcpy(dummybuf, a, 2 * pagesize);
+    memcpy(dummybuf, b, pagesize);
+    memcpy(dummybuf, c, 2 * pagesize);
+
+    munmap(a, 2 * pagesize);
+    munmap(b, pagesize);
+    munmap(c, 2 * pagesize);
+}
+
 int main(int argc, char **argv)
 {
 	char tempname[] = "/tmp/.cmmapXXXXXX";
@@ -468,7 +505,7 @@ int main(int argc, char **argv)
 
 	/* Assume pagesize is a power of two.  */
 	pagemask = pagesize - 1;
-	dummybuf = malloc (pagesize);
+	dummybuf = malloc (pagesize * 2);
 	printf ("pagesize=%u pagemask=%x\n", pagesize, pagemask);
 
 	test_fd = mkstemp(tempname);
@@ -496,6 +533,7 @@ int main(int argc, char **argv)
 	check_file_fixed_eof_mmaps();
 	check_file_unfixed_eof_mmaps();
 	check_invalid_mmaps();
+    check_shrink_mmaps();
 
 	/* Fails at the moment.  */
 	/* check_aligned_anonymous_fixed_mmaps_collide_with_host(); */