linux-kernel - [PATCH v2 3/3] selftests/mm: virtual_address

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Message-Id: <20250110-virtual_address_range-tests-v2-3-262a2bf3c3d0@linutronix.de>
Date: Fri, 10 Jan 2025 14:05:52 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Shuah Khan <shuah@...nel.org>, Dev Jain <dev.jain@....com>, 
 Thomas Gleixner <tglx@...utronix.de>, David Hildenbrand <david@...hat.com>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 kernel test robot <oliver.sang@...el.com>
Subject: [PATCH v2 3/3] selftests/mm: virtual_address_range: Avoid reading
 VVAR 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.

Skip the various vvar mappings in virtual_address_range to avoid the issue.

Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@intel.com
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 tools/testing/selftests/mm/virtual_address_range.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index 4fc1c21a5e218eaec4d059b75c31a21dd4e8a215..993990aba56fc986c42084ffa91973558aa07e87 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -152,6 +152,10 @@ 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 (vma_name && !strncmp(vma_name, "[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