selftests/mm: virtual_address_range: avoid reading from VM_IO mappings

JIRA: https://issues.redhat.com/browse/RHEL-88165
Conflicts:
  * Minor merge conflict of check_vmflag_io(), no functional changes.

commit 3bd6137
Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Date:   Tue Jan 14 17:06:48 2025 +0100

    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 e93d252 ("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 <oliver.sang@intel.com>
    Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@intel.com
    Fixes: e93d252 ("x86/vdso: Split virtual clock pages into dedicated mapping")
    Fixes: 0104096 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
    Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
    Suggested-by: David Hildenbrand <david@redhat.com>
    Link: https://lore.kernel.org/lkml/e97c2a5d-c815-4936-a767-ac42a3220a90@redhat.com/
    Acked-by: David Hildenbrand <david@redhat.com>
    Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
    Cc: Dev Jain <dev.jain@arm.com>
    Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Li Wang <liwang@redhat.com>

Author: wangli5665

tools/testing/selftests/mm/virtual_address_range.c

@@ -15,6 +15,7 @@
 #include <sys/time.h>
 #include <fcntl.h>
 
+#include "vm_util.h"
 #include "../kselftest.h"
 
 /*
@@ -159,6 +160,9 @@ static int validate_complete_va_space(void)
 		if (prot[0] != 'r')
 			continue;
 
+		if (check_vmflag_io((void *)start_addr))
+			continue;
+
 		/*
 		 * Confirm whether MAP_CHUNK_SIZE chunk can be found or not.
 		 * If write succeeds, no need to check MAP_CHUNK_SIZE - 1

tools/testing/selftests/mm/vm_util.c

@@ -256,6 +256,30 @@ unsigned long get_free_hugepages(void)
 	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;
+	}
+}
+
 int detect_hugetlb_page_sizes(size_t sizes[], int max)
 {
 	DIR *dir = opendir("/sys/kernel/mm/hugepages/");

tools/testing/selftests/mm/vm_util.h

@@ -53,6 +53,7 @@ int uffd_register(int uffd, void *addr, uint64_t len,
 int uffd_unregister(int uffd, void *addr, uint64_t len);
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls);
+bool check_vmflag_io(void *addr);
 
 /*
  * On ppc64 this will only work with radix 2M hugepage size