selftests/mm: virtual_address_range: avoid reading from VM_IO mappings

The virtual_address_range selftest reads from the start of each mapping
listed in /proc/self/maps.  However not all mappings are valid to be
arbitrarily accessed.

For example the vvar data used for virtual clocks on x86 [vvar_vclock] can
only be accessed if 1) the kernel configuration enables virtual clocks and
2) the hypervisor provided the data for it.  Only the VDSO itself has the
necessary information to know this.  Since commit e93d2521b27f ("x86/vdso:
Split virtual clock pages into dedicated mapping") the virtual clock data
was split out into its own mapping, leading to EFAULT from read() during
the validation.

Check for the VM_IO flag as a proxy.  It is present for the VVAR mappings
and MMIO ranges can be dangerous to access arbitrarily.

Link: https://lkml.kernel.org/r/20250114-virtual_address_range-tests-v4-4-6fd7269934a5@linutronix.de
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Signed-off-by: Thomas Weißschuh <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Acked-by: David Hildenbrand <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Shuah Khan (Samsung OSG) <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 24 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index b16f9d3adc69..a36734fb62f3 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -400,3 +400,27 @@ unsigned long get_free_hugepages(void)
 	fclose(f);
 	return fhp;
 }
+
+bool check_vmflag_io(void *addr)
+{
+	char buffer[MAX_LINE_LENGTH];
+	const char *flags;
+	size_t flaglen;
+
+	flags = __get_smap_entry(addr, "VmFlags:", buffer, sizeof(buffer));
+	if (!flags)
+		ksft_exit_fail_msg("%s: No VmFlags for %p\n", __func__, addr);
+
+	while (true) {
+		flags += strspn(flags, " ");
+
+		flaglen = strcspn(flags, " ");
+		if (!flaglen)
+			return false;
+
+		if (flaglen == strlen("io") && !memcmp(flags, "io", flaglen))
+			return true;
+
+		flags += flaglen;
+	}
+}