[PATCH 2/3] selftests/mm: virtual_address_range: Avoid reading VVAR mappings

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

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 can only be
accessed if 1) the kernel configuration enables virtual clocks and 2)
the hypervisor provided the data for it, which can only determined by
the VDSO code itself.
Since commit e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
the virtual clock data was split out into its own mapping, triggering
faulting accesses by virtual_address_range.

Skip the various vvar mappings in virtual_address_range to avoid errors.

Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Cc: stable@vger.kernel.org
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@intel.com
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 tools/testing/selftests/mm/virtual_address_range.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index d7bf8094d8bcd4bc96e2db4dc3fcb41968def859..484f82c7b7c871f82a7d9ec6d6c649f2ab1eb0cd 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -116,10 +116,11 @@ static int validate_complete_va_space(void)
 
 	prev_end_addr = 0;
 	while (fgets(line, sizeof(line), file)) {
+		int path_offset = 0;
 		unsigned long hop;
 
-		if (sscanf(line, "%lx-%lx %s[rwxp-]",
-			   &start_addr, &end_addr, prot) != 3)
+		if (sscanf(line, "%lx-%lx %4s %*s %*s %*s %n",
+			   &start_addr, &end_addr, prot, &path_offset) != 3)
 			ksft_exit_fail_msg("cannot parse /proc/self/maps\n");
 
 		/* end of userspace mappings; ignore vsyscall mapping */
@@ -135,6 +136,10 @@ static int validate_complete_va_space(void)
 		if (prot[0] != 'r')
 			continue;
 
+		/* Only the VDSO can know if a VVAR mapping is really readable */
+		if (path_offset && !strncmp(line + path_offset, "[vvar", 5))
+			continue;
+
 		/*
 		 * Confirm whether MAP_CHUNK_SIZE chunk can be found or not.
 		 * If write succeeds, no need to check MAP_CHUNK_SIZE - 1

-- 
2.47.1