kselftest: vm: fix mdwe's mmap_FIXED test case

[ Upstream commit a27e2e2d465e4ed73371974040689ac3e78fe3ee ]

I checked with the original author, the mmap_FIXED test case wasn't
properly tested and fails.  Currently, it maps two consecutive (non
overlapping) pages and expects the second mapping to be denied by MDWE but
these two pages have nothing to do with each other so MDWE is actually out
of the picture here.

What the test actually intended to do was to remap a virtual address using
MAP_FIXED.  However, this operation unmaps the existing mapping and
creates a new one so the va is backed by a new page and MDWE is again out
of the picture, all remappings should succeed.

This patch keeps the test case to make it clear that this situation is
expected to work: MDWE shouldn't block a MAP_FIXED replacement.

Link: https://lkml.kernel.org/r/20230828150858.393570-3-revest@chromium.org
Fixes: 4cf1fe34fd18 ("kselftest: vm: add tests for memory-deny-write-execute")
Signed-off-by: Florent Revest <revest@chromium.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Ayush Jain <ayush.jain3@amd.com>
Cc: Alexey Izbyshev <izbyshev@ispras.ru>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: Topi Miettinen <toiwoton@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
index bc91bef5d254e5770d29188aae81f1259829b511..0c5e469ae38fab486ab524312a3d2a8f4bd491ad 100644 (file)
--- a/tools/testing/selftests/mm/mdwe_test.c
+++ b/tools/testing/selftests/mm/mdwe_test.c
@@ -168,13 +168,10 @@ TEST_F(mdwe, mmap_FIXED)
        self->p = mmap(NULL, self->size, PROT_READ, self->flags, 0, 0);
        ASSERT_NE(self->p, MAP_FAILED);
 
-       p = mmap(self->p + self->size, self->size, PROT_READ | PROT_EXEC,
+       /* MAP_FIXED unmaps the existing page before mapping which is allowed */
+       p = mmap(self->p, self->size, PROT_READ | PROT_EXEC,
                 self->flags | MAP_FIXED, 0, 0);
-       if (variant->enabled) {
-               EXPECT_EQ(p, MAP_FAILED);
-       } else {
-               EXPECT_EQ(p, self->p);
-       }
+       EXPECT_EQ(p, self->p);
 }
 
 TEST_F(mdwe, arm64_BTI)