Fix false alarm on non-page-aligned size for mprotect

src/libos/src/vm/process_vm.rs

@@ -373,6 +373,12 @@ impl ProcessVM {
     }
 
     pub fn mprotect(&self, addr: usize, size: usize, perms: VMPerms) -> Result<()> {
+        let size = {
+            if size == 0 {
+                return Ok(());
+            }
+            align_up(size, PAGE_SIZE)
+        };
         let protect_range = VMRange::new_with_size(addr, size)?;
         if !self.process_range.range().is_superset_of(&protect_range) {
             return_errno!(ENOMEM, "invalid range");

test/mmap/main.c

@@ -9,6 +9,7 @@
 #include <assert.h>
 #include <string.h>
 #include <fcntl.h>
+#include <sys/syscall.h>
 #include "test.h"
 
 // ============================================================================
@@ -1061,6 +1062,35 @@ int test_mprotect_with_invalid_prot() {
     return 0;
 }
 
+int test_mprotect_with_non_page_aligned_size() {
+    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+    void *buf = mmap(NULL, PAGE_SIZE * 2, PROT_NONE, flags, -1, 0);
+    if (buf == MAP_FAILED) {
+        THROW_ERROR("mmap failed");
+    }
+
+    // Use raw syscall interface becase libc wrapper will handle non-page-aligned address
+    // and will not cause failure.
+    // Raw mprotect syscall with non-page-aligned address should fail.
+    int ret = syscall(SYS_mprotect, buf + 10, PAGE_SIZE, PROT_WRITE);
+    if (ret == 0 || errno != EINVAL) {
+        THROW_ERROR("mprotect with non-page-aligned address should fail with EINVAL");
+    }
+
+    // According to man page of mprotect, this syscall require a page aligned start address, but the size could be any value.
+    // Raw mprotect syscall with non-page-aligned size should succeed.
+    ret = syscall(SYS_mprotect, buf, PAGE_SIZE + 100, PROT_WRITE);
+    if (ret < 0) {
+        THROW_ERROR("mprotect with non-page-aligned size failed");
+    }
+
+    // Mprotect succeeded and the pages are writable.
+    *(char *)buf = 1;
+    *(char *)(buf  + PAGE_SIZE) = 1;
+
+    return 0;
+}
+
 // ============================================================================
 // Test suite main
 // ============================================================================
@@ -1100,6 +1130,7 @@ static test_case_t test_cases[] = {
     TEST_CASE(test_mprotect_with_zero_len),
     TEST_CASE(test_mprotect_with_invalid_addr),
     TEST_CASE(test_mprotect_with_invalid_prot),
+    TEST_CASE(test_mprotect_with_non_page_aligned_size),
 };
 
 int main() {